Peragallo and Peragallo 1897–1908, p. 310, pl. 78, fig. 6; Hustedt 1931–1959, p. 233, fig. 720; Sullivan and Wear 1995, p. 181, figs 1–8; Navarro 1982, p. 260, figs 61–63; Navarro and Lobban 2009, p. 136; Lobban et al. 2012, p. 259, pl. 15, figs 4, 5, pl. 16, figs 1, 2; Park et al. 2018, p. 105, fig. 5.

Hustedt (1931–1959) described this species as linear with ends somewhat narrowed, 200–700 µm long, 15–25 µm wide, 9–10 transapical costae in 10 µm, two rows of areolae between each costa; two or three longitudinal costae and an inner layer, dividing the wall into a series of chambers, each with a single foramen in the inner wall, resulting in three or four chambers. The series of foramina have been described as rows of “pearls,” parallel to the longitudinal lines of the annulus with its underlying costae and sometimes a central costa. Hustedt (1931–1959) specifically referred to a (3^rd) longitudinal costa down the middle sometimes, and his fig. 720b shows two rows of foramina between the annular lines, suggesting a costa between them, as the chambers were supposed to have only a single opening. A similar situation is seen in Sullivan and Wear (1995: fig. 4). Hustedt (1931–1959) showed two rows of areolae between the transapical costae, but Sullivan and Wear (1995) reported only one and noted the discrepancy. With SEM they showed that the valvocopula had a prominent notch in the advalvar side and a fimbriate edge to the pars interior. They noted that the areolae at the poles were smaller, circular, less dense and more loosely organized but not an apical pore field.

Guam: GU44BH-5!, GU26A!, GU52R-2!. Federated States of Micronesia: Yap: Y39A!, Y42-1!. Marshall Islands: Jaluit Atoll: J5!; Bakir Atoll: BA2!.

Valves linear with broadly rounded poles, 201–300 µm long, 22–24 µm wide, striae 8–10 in 10 µm, isopolar in both valve and girdle view (Fig. 1A). Plastids numerous, lenticular, displaying peristrophy and karyostrophy depending on light intensity (Suppl. material 3: Fig. S1). Three or five longitudinal lines seen in two focal planes (Fig. 1B, C): if five, the annulus, subtending a longitudinal costa, on the valve face (not hidden at the valve margin), a central line where the offset striae meet; between these, on the inner wall, two rows of foramina (Fig. 1B–D). If three lines, one central row of foramina with no longitudinal costa (Fig. 1F). Two additional rows of foramina along the angle of the valve–mantle junction seen in SEM but obscured in LM (Fig. 1D, F). The pattern of costae underlying the inner wall can be traced in Fig. 1D and seen directly in Fig. 1E. We have also seen specimens with one row of foramina along the midline (Fig. 1F). Commonly one or two longitudinal depressions in valve surface, giving a shallow v (Fig. 1I) or w profile. Striae comprising single row of oval areolae between each transapical costa (Fig. 1C, E, G); loose rows of smaller, circular areolae at the poles, especially noticeable on mantle (Fig. 1I). Narrow pseudoseptum around poles (Fig. 1D, E), elsewhere the double wall forms a thick rim (Fig. 1G). Three girdle bands as follows (Fig. 1F–J). Valvocopula with line of small pores along edge of pars interior, usually obscured in girdle view, deflecting asymmetrically inwards at pole (Fig. 1F), corresponding to location of the notch on advalvar side, which however, is nearly central (Fig. 1I). Interior edge of valvocopula with short fimbriae (Fig. 1G, J). Copula with long fringe of fimbriae at pole, overlapping the valvocopula (Fig. 1H), as described by Sullivan and Wear (1995); an irregular line of pores along abvalvar margin of copula in some specimens (Fig. 1J, arrowhead). Narrow pleura (Fig. 1I, J) with a row of small pores on pars interior.

Figure 1. 

Micrographs of Ardissonea formosa A whole frustule, length 380 µm, girdle view in SEM, showing isopolarity (Guam: GU44BH-5) B, C light micrographs at two focal planes, apical part of valve showing internal foramina (B arrows), annulus and central costa (C arrowheads) (Jaluit: J5) D SEM of internal aspect showing inner wall with foramina and narrow apical pseudoseptum (arrow) (GU44BJ-2) E internal aspect of valve pole with inner wall missing, showing a central longitudinal costa (arrow) (Yap: Y42-1) F internal view of pole of valve with valvocopula, showing double wall with one central line of foramina, transverse and longitudinal costae showing through the interior wall, and the pores of the valvocopula asymmetrically deflected around the notch (arrow) (Y42-1) G broken frustule showing details of wall structure—inner and outer layers separated by costae, inner layer with foramina—in relation to valvocopula and copula (GU44BJ-4) H pole of frustule showing long fimbriae at tip of copula (arrow) (GU75A-4) I detail of frustule pole in girdle view, showing the three girdle bands with no pores in the external surfaces and the groove in the valvocopula apex (arrow) (GU44BH-5) J details of mid portion of frustule in girdle view, showing a line of pores on the edge of the copula (arrowhead) and on the pleura, and the fimbriate inner edge of the valvocopula (arrow) (GU52R-2). Abbreviations used on figures: VC = valvocopula; cop = copula; pl = pleura. Scale bars: 100 µm (A); 10 µm (B–C, I); 5 µm (D–H, J).

The biseriate striae described by Hustedt (1931–1959) and the uniseriate striae in Sullivan and Wear’s (1995) materials suggest that they were observing different species. Sullivan and Wear (1995) observed only two bands on the epicingulum and none on the hypocingulum but we observed the pleura. Ardissonea s.s. superficially resembles Synedra in the current restricted sense (= Catacombas) in shape and double wall but differs in lacking rimoportulae and polar pore fields.

Differing from A. formosa in small, lanceolate valves with 16–17 striae in 10 µm and externally porate copula.

Valves lanceolate, weakly rostrate, 46–103 µm long, 7–10 µm wide, striae parallel, 16–17 in 10 µm (Fig. 2A–C), meeting in an irregular sternum (Fig. 2B, C). Isopolar in both valve and girdle views (Fig. 2A–E). Areolae oval, apically elongate. Two or three longitudinal costae appearing through internal plate (Fig. 2F, G); correspondingly three or four rows of foramina are present. Fig. 2F suggests a costa under sternum. Valve with rim expanded into asymmetric pseudoseptum at poles (Fig. 2F). Girdle bands: Valvocopula pars interior at pole developed asymmetrically, matching the pseudoseptum and with deep notch in advalvar surface (Fig. 2G, arrow, 2H). One line of pores on pars interior, exterior plain (Fig. 2D, I). Copula (Fig. 2D, I) with 1–3 irregular rows of pores on the exterior, pars interior with a row of small pores partially exposed to exterior and a fimbriate inner edge, particularly well developed at poles (Fig. 2I). Pleura narrow with single row of pores, continuous along the cell length (Fig. 2D, E).

Figure 2. 

Ardissonea densistriata sp. nov. A holotype from Bikar Atoll, BA1 (LM) B, C external views of valves in SEM; arrows on B point to location of annulus (B Y42-1, C BA-1) D, E external view of two ends of same frustule showing isopolarity; arrow on E points to apical notch in VC (J5) F, G internal views of valves with one and two middle lines of foramina, arrows showing asymmetrical pseudoseptum on valve in F and asymmetrical pole of the valvocopula in G; arrowheads point to longitudinal costae (BA1) H, I external views of frustules from Bikar and Jaluit, respectively, showing profile of pole of valvocopula in H and apical comb of fimbriae on copula in I (arrow). Scale bars: 10 µm (A–C); 5 µm (D, E); 2.5 µm (F–I).

(designated here). Specimen at 16.6 mm E and 11.5 mm S of the mark on slide 2911, deposited at ANSP accession # ANSP-GC20089. Fig. 2A.

Phycobank http://phycobank.org/103235.

Marshall Islands: Bikar Atoll, 12.223°N, 170.096°E. Filamentous seaweed sample from shallow subtidal farmer fish territory in the lagoon, precise location not recorded. Collection number BA1, October 2019. Andrew McInnis leg.

Federated States of Micronesia: Yap: Y42-1!, Y42-3!.

Densus + striatus (Latin) = densely striated, in comparison to congeners.

Given the small number of double-walled Ardissonea species, this species is easily distinguished by the small size, lanceolate shape and relatively high stria density. It is more readily confused in our flora with Grunowago pacifica sp. nov. (see below), but in LM the latter can be distinguished by the lack of an inner wall (indicated by absence of foramina) and presence of a longitudinal costa along the midline, in SEM by the extensive poration on the copula. To date this species has not been observed in Guam samples. A different lanceolate, double-walled Ardissonea was observed in samples from Chuuk and Jaluit, with stria density 9–12 µm, length 116–211 µm, but we do not have complete information from either population. These samples are similar in shape and stria density to a Red Sea species ‘Ardissonea AdnU041’ observed by Sabir et al. (unpublished: http://www.protistcentral.org/Taxa/get/taxa_id/586376 and Ashworth, personal communication). This unnamed species is 83–125 µm long and has no external poration on the girdle bands (as in A. formosa). The sequence data have been published as UTKSA0041, shown in our Fig. 33, sister to A. formosa.

Peragallo and Peragallo 1897–1908, p. 310, pl. 79, fig. 1; Hustedt 1931–1959, p. 232, fig. 719; Navarro 1982, p. 260, figs 59, 60; Poulin et al. 1986, figs 28–30; Poulin et al. 1987, p. 2689, figs 1–11; Pickett-Heaps et al. 1991, figs 9–19; Lobban et al. 2012, p. 259, pl. 15, figs 1–3; Davidovich et al. 2017, figs 1, 2.

Valves 200–700 µm long, 8–20 µm wide, linear but slightly wider at the middle and poles; 11 striae in 10 µm but much closer in “transitional forms such as var. dalmatica” (Hustedt 1931–1959). Internally with prominent costae developed on every virga except at poles, and with two longitudinal costae corresponding to location of annular ring; spines completely absent. Edge of valve recurved into a pseudoseptum; an interpretive diagram in Pickett-Heaps et al. (1991) shows the relationship between the valve, valvocopula, copula and a small, plain pleura at the pole. Valvocopula and copula have interior comb-like fringe, exterior part with four or more rows of pores arranged decussately; an apical groove between the pseudoseptum and a fold in the valvocopula provides an exit for attachment mucilage (Poulin et al. 1987; Pickett Heaps et al. 1991) but Pickett-Heaps et al. (1991) argued that this groove was a very different structure from the apical pore in A. formosa as shown by Round et al. (1990). Shorenko et al. (2016) obtained auxospores of this species and determined a maximum length of 678 µm.

Guam: GU44Y-13!, GU44AV-8!, GU44BJ-4!, GU56A-2!. Federated States of Micronesia: Chuuk: TK4, TK28. Marshall Islands: M1!

Specimens from Guam and Chuuk 220–350 µm long, 11–16 µm wide, isopolar in both valve and girdle views, striae 16–19 in 10 µm, slightly offset on internal and external sides of annulus (Fig. 3A, B). Annulus well separated from valve-margin junction and clearly visible in LM and SEM, including around the poles (Fig. 3A, B). Pseudoseptum at poles (Fig. 3B) and rim along entire valve (Fig. 3C), facing pars interior of the valvocopula. Apical spines not observed (Fig. 3A, D, H). Costae well developed (Fig. 3B, C). Three girdle bands present (Fig. 3D): valvocopula fimbriate (Fig. 3D, F–H), forming a slot on one side of the pole and a sharper notch on the other (Fig. 3D arrows, Fig. 3H); pores on pars interior passing across back of flange, elongated into slits at pole, clearly closed at inner margin (Fig. 3G arrow) and pars interior expanded and recurved at pole (Fig. 3F). Pores on pars exterior discontinuous around pole in front of the groove (Fig. 3F–H). Copula (Fig. 3D, I, J) broader and flat, even at pole, with up to 10 rows of circular pores in a decussate pattern; pars interior fimbriate with free fimbriae highly developed at pole, where they overlap the valvocopula, elsewhere shorter fimbriae arising from fused base (arrows, Fig. 3I, J). Small difference in shape, number of rows of pores and length of fimbriae between Fig. 3I and J may be due to origin of material (Fig. 3D and 3I are from Chuuk wild samples, Fig. 3J from Guam culture) but copulae from wild material from Guam (not shown) also had >6 rows of pores. Pleura (Fig. 3D) fimbriate, an apical cap extending along the valve as a very narrow ribbon.

Figure 3. 

Ardissonea crystallina A, B external and internal views of valve poles from, respectively Majuro (M1) and Guam (GU44J-4), showing pseudoseptum (B arrow) C internal SEM view (60° tilt) of broken valve showing internal costae including longitudinal costa subtending the annulus (arrowhead) and continuous rim on valve (arrow) (Chuuk: TK4) D, E pole of frustule in girdle view and tilted to 45° to confirm identity; showing the asymmetrical gaps between the pseudoseptum and valvocopula (arrows) (GU75A-4) F, G polar portions of valvocopulae from advalvar side and abvalvar sides, respectively, arrow on F showing where pores along edge of pars interior move to the back of the gap, arrowhead on G showing that slits do not form an open comb (Chuuk: TK4) H polar view of pole with valvocopula showing the asymmetrical gaps (TK4) I, J poles of copulae from wild material (TK4) and culture (GU44AV-8), respectively, arrows indicating fused bases of fimbriae away from the pole. Scale bars: 10 µm (D, E, I); 5 µm (A–C, F–H, J).

Ardissonea crystallina cannot remain in Ardissonea sensu stricto and will be transferred in the Taxonomic Revisions section at the end of the paper. Álvarez-Blanco and Blanco (2014) show Mediterranean specimens of Ardissonea dalmatica (Kützing) De Toni, restored to species status without comment, but the length ranges only up to 151 µm. There was a row of papillae/spines around the pole, not present in our material and the length range in the literature is 100–151 µm, but the stria density matches our specimens more closely. We leave our identification at A. crystallina pending broader study. Although Hustedt (1931–1959) noted A. crystallina as distributed on coasts of warmer waters, Poulin et al. (1987) reported it as the only Ardissonea on the coast of Québec, an area that is far from tropical. Likewise, Shorenko et al. (2016) and Davidovich et al. (2017) collected it from the Black Sea. We do not agree with Pickett-Heaps et al. (1991) that there is a fundamental difference in the architecture at the pole of the valvocopulae of A. formosa and A. crystallina as both involve irregularities in the surface of the flange of the valvocopula where it lies below the pseudoseptum.

Janisch and Rabenhorst 1863, p. 13, pl. 2, fig. 6; Grunow 1877, p. 169, pl. 194, fig. 3a, b, c, d ; Peragallo and Peragallo 1897–1908, p. 313, pl. 78, figs 1, 2 (as S. cuneata Grunow); Hustedt 1914 in Schmidt et al. (1874–1959), pl. 305, figs 32, 33; Hustedt 1931–1959, p. 231, fig. 723; Cheng and Gao 2011, figs 147, 148; Hein et al. 2008, pl. 14, fig. 3, pl. 15, fig. 1; Hernández-Almeida et al. 2013, figs 39–42 (as Synedrosphenia cuneata).

The valve shape as shown by both Grunow (1877) and Hustedt (1914, 1931–1959) has a basal part with nearly parallel sides that then tapers wider, flaring more abruptly near the apical pole. Hustedt gave length as 250–475 µm, maximum width 27–36 µm, basal and apical stria densities 12 and 14 in 10 µm, respectively. Striae change abruptly from parallel to radiate where the apical pole narrows. Transapical costae on the virgae often continuous across the valve and obscuring the midline; a longitudinal rib near each margin. Round et al. (1990: 444) noted that in Synedrosphenia stria density is higher on the girdle bands than on the valve (Fig. 10A), whereas in Climacosphenia it is lower on the girdle bands (Fig. 28A). This holds true for all our species.

Guam GU44Y-13!, GU44BD-4!, GU44BH-5!, GU 44BJ-2!, GU44BJ-4!. Federated States of Micronesia: Chuuk: TK28!; Yap: Y42-1!. Marshall Islands: Jaluit, J5!.

Frustules heteropolar, cuneate in both valve and girdle view, numerous small, oblong plastids (Fig. 4A–D). Valve margins parallel near basal pole, then gradually widening with slight flare below subrostrate apical pole (Fig. 4E, F). Length 255– >414 µm, greatest width 27–29 µm, stria densities in 10 µm 13–14 basal, 14–16 apical. Striae parallel except changing abruptly to radial at apical pole with several interpolated short striae (Fig. 4B, E, G); areolae circular. Annulus near valve–mantle junction but clearly visible in both LM and SEM (Fig. 4B, E–I), continuous around the poles (Fig. 4E, H, J). Internal costae underlie annulus and virgae, except at the poles. Three girdle bands present (Figs 4F, 5A). Valvocopula (Figs 4J, K, 5B–E) with about 4 longitudinal rows of pores on pars exterior, decreasing to two near basal pole, pars interior with a fimbriate margin comprising a shelf with a single row of pores and a groove; poles with asymmetrical notch (Figs 4C, K, 5A). Copula (Figs 4J, K, 5A, F, G) pars interior with longitudinal line of pores along edge, the rest of pars interior plain with fringe of fimbriae, longer around apical and basal poles (Figs 4K, 5G). Copula pars exterior abruptly narrowed at apical pole, pores arranged in ± decussate striae across the band reaching abvalvar margin and forming fimbriae; no pores around poles. Copulae in Guam specimens tending to form slits (Fig. 4D and Fig. 5A black arrows), not observed in Chuuk specimens (Fig. 5F, G). Pleura visible as apical cap (Fig. 4F), seemingly lost during cell division (Fig. 5A; compare Fig. 12E, F).

Figure 4. 

Synedrosphenia gomphonema A live specimen in valve view showing heteropolar cell shape and plastids (GU44BJ-4) B apical portion of cleaned valve in LM showing change in stria orientation where cell narrows (GU44BD-4) C, D recently divided frustule in girdle view with details of basal and apical poles, respectively, showing heteropolarity; black arrow indicates slit formation on the copula (GU44BJ-4) E, F valvar view of frustule at 0° and 60° tilt, respectively, arrows on E showing location of annulus, labels on F naming the girdle bands (abbreviations as before) G–I apical and basal portions of valve, internal view tilted 60°, showing pseudosepta at poles (H, I arrows) and transverse and longitudinal costae (TK4); inset (H) shows tip of same valve at 0° tilt with lack of costae between the last few striae but continuation of annulus J, K basal portions of a broken, recently divided frustule from Chuuk, viewed at 0° and 60° tilt, respectively, valves and girdle bands of one daughter cell with one valve of other daughter on top; arrow shows the notch between valve and valvocopula (TK4). Scale bars: 25 µm (A); 10 µm (B–G, I); 5 µm (H, J).

Figure 5. 

Synedrosphenia gomphonema cont. A apical pole of frustule in polar view tilted 60°, showing the valvocopula and copula of the hypocingulum (HVC and Hcop) largely hidden under the epicingulum bands (EVC and Ecop); the pleurae are missing and in the space where they were the tips of the newly formed valves are visible (long arrows). Short white arrows point to the apical notches slightly off-center in opposite directions; black arrow shows some slit formation in the copula (GU44BJ-4) B–E valvocopula with apical pole in advalvar view (B) showing recurved pars interior at the tip, abvalvar view (C), basal pole (D) and middle (E), all showing fimbriae (B, D, E from same specimen in GU44BI-4, C from TK4) F, G copula middle and apical pole, respectively, external view, showing fimbriae developing on the abvalvar edge of the pars exterior (arrow) (TK4). Scale bars: 10 µm (A, E, F, G); 5 µm (B–D).

A frustule of Sceptroneis cuneata in remnants of Grunow 639 (Fig. 6), showed the valve and copula. Valve stria densities were lower than in our material: basal 12, apical 13 in 10 µm. The copula differed in having a hyaline abvalvar border with no tendency to form fimbriae (Fig. 6D, E) and a longer hyaline area at the basal pole (Fig. 6E vs Fig. 4F). The apical cap of the pleura may be smaller than in our specimens. A valve apical pole with part of the valvocopula (Fig. 6F, G) had 11 striae in 10 µm and there were no pores in the exterior, in contrast to Guam specimens.

Figure 6. 

Specimens of Sceptroneis cuneata from Grunow’s Honduras sample A–C whole frustule at 0° tilt and details of basal pole and apical poles, respectively, showing internal costae and the copula; arrows point to long fimbriae overlapping valvocopula at both poles D, E same specimen, tilt = 60°, details of apical and basal poles, respectively, showing copula, including shallow cut-away matching smaller pleura (arrow on D), hyaline abvalvar margin of copula (black arrow on D), and reduced poration near basal pole (arrow on E) F apical part of valve in external view G valvocopula associated with same specimen. Scale bars: 50 µm (A); 10 µm (B–F); 5 µm (G).

There are too many differences from Grunow’s specimens to identify our species as Sceptroneis cuneata. We also cannot confirm whether our specimens match Synedrosphenia gomphonema without SEM of authentic specimens. The taxonomy of Synedrosphenia is convoluted. As explained by Fourtanier and Kociolek (1999):

“Originally described (and validly published) as a subgenus of Synedra: Synedra subgenus Synedrosphenia H. Peragallo in H. and M. Peragallo 1900 [Peragallo and Peragallo 1897–1908], p. 308, 312. Three species were included, Sceptroneis [Synedra] cuneata Grun., S. clavata Grev. and S. dubia Grun. and no type was designated. Although Azpeitia 1911, p. 220 introduces the name as “El genero ó subgenero Synedrosphenia” (the genus or subgenus Synedrosphenia) , he treats it as a genus when describing his new species Synedrosphenia giennensis. Although S. giennensis Azpeitia is the only species formed as binomial with Synedrosphenia in Azpeitia 1911, Azpeitia, in his treatment of Synedrosphenia also clearly included the 3 species that constituted Peragallo’s subgenus (but did not make transfers to genus Synedrosphenia) . No type was designated by Azpeitia. The generic name cannot be attributed directly to Azpeitia because he did not provide a generic description. The authorship of Synedrosphenia is therefore “(H. Peragallo in H. Perag. and M. Perag.) Azpeitia,” and the type has to be chosen among the species originally included in the subgenus by Peragallo. The choice of S. giennensis as the type species by Round, Crawford and Mann (1990) p. 444 and 704 is therefore untenable.”

Hustedt (1931–1959) very clearly synonymized Sceptroneis cuneata into Synedrosphenia gomphonema (1931–1959, fig. 723, pp. 220–221 in Jensen’s (1985) translation, pp. 241–242 in orig.). The drawing in Janisch and Rabenhorst (1863) is, as Hustedt (1931–1959) said, “very schematic and erroneous to be sure,” showing a prominent sternum, but Hustedt based his synonymy on examination of many specimens from both Janisch and Grunow, both of whom worked on collections from Honduras. The other two species, S. clavata and S. dubia, are poorly known, perhaps not seen since their original descriptions, both characterized as very rare, and perhaps not even attributable to this genus. We thus propose Sceptroneis cuneata Grunow as the lectotype, below, recognizing the synonymy with S. gomphonema as the current name for the Honduras species, but pending evidence from Janisch and Rabehnorst’s materials to test whether our species is the same. Synedrosphenia giennensis Azpeitia (1911, p. 219, pl. 6, figs 1, 2) was based on LM of a single clavate valve, maximum width ¼ of the way from one end, costae between striae not always continuous across the valve. Azpeitia made no mention of longitudinal costae. The dimensions were 195 × 35 µm, 12 striae in 10 µm, areolae 19–20 in 10 µm. This does appear to belong in Synedrosphenia but certainly needs further study.

Valve spathulate, heteropolar, differing from S. parva and S. gomphonema in valve shape and in the fimbriate pars exterior of the copula.

Cells heteropolar, probably attached by basal pole to seaweeds. Valves spathulate, 214–277 µm long with linear, wider apical portion 12–14 µm wide, narrowing abruptly about halfway down the valve and then more gradually to 6 µm near the basal pole, which is weakly inflated to 7 µm (Fig. 7A–C). Both poles bluntly rounded. Striae parallel except weakly radiating at apical pole, 21 in 10 µm; areolae circular, 25 in 10 µm (Fig. 7D–F). Internally costae on all virgae except at poles (Figs 7G, 8D, E). Bifacial annulus indicated only by an offset between striae on valve face and mantle (Fig. 7D, oval). There was a junction down the midline of the valve where the inward-growing striae met but no sternum (Fig. 7B–E).

Figure 7. 

Synedrosphenia bikarensis sp. nov. (all from Bikar sample BA5) A–C holotype whole valve, basal and apical portions, respectively (LM) D–F external SEM views of apical, middle and basal portions, respectively, of a frustule, showing valve structure. Oval in D highlights area where break in striae across the annulus can be seen, even though the annulus is not readily visible G, H internal views of apical pole with pseudoseptum (arrow) and middle portion (H) showing transverse costae and the lack of a longitudinal costa under the annulus I, J frustule in girdle view, apical and basal portions, respectively, showing heteropolarity and girdle bands of the epicingulum. Arrows mark the notches visible on the hypovalvocopula at the apical pole and epivalvocopula at the basal pole, indicating the asymmetry. Scale bars: 25 µm (A); 10 µm (B, C, H); 5 µm (D–G, I, J).

Girdle bands: Cingulum comprising two large, closed bands and a large apical cap (pleura) (Figs 7I, J, 8). Valvocopula porate (Figs 7I, J, 8A–E); the pars interior forming a sturdy comb (Fig. 8A–C) that matched up with the internal costae of the valve (Fig. 8D), though it was not clear whether they aligned or interdigitated with the costae. This was followed by an internal ridge and an adjacent series of pores, often hidden under the valve (Figs 7I, J, 8B, C). The pars interior was modified asymmetrically at each pole (Fig. 8D, E), with a shelf supporting a prominent asymmetrical notch (Fig. 7I, J and Fig. 8A, C). Apical and basal asymmetries were on opposite sides of the valvocopula (Fig. 8D, E, arrows) and the symmetry on the hypotheca was the mirror image of the epitheca (Fig. 7I, J, arrows). Pars exterior with three irregular rows of pores, 30 in 10 µm, reducing to two and then one at the basal pole. The copula also had a comb along inner edge of pars interior and a row of pores just under the overlapping valvocopula (Fig. 8F, G). Copula internal comb continued around the apical pole; pars exterior dominated by a series of long slits (rimae) that often extended to abvalvar margin (Figs 7I, J, 8G), resulting in a fringe along the edge of the cingulum except at poles. Both valvocopula and copula narrowed at the poles, leaving a space filled by the pleura, which is possibly a continuous band (Fig. 7I, J). We did not see the pars interior of the pleura but it is likely to be fimbriate (see S. parva below).

Figure 8. 

Synedrosphenia bikarensis, cont. A–C valvocopula: apical portion in advalvar view (A) with asymmetrical notch at apical pole (arrow), middle portion (B) with long sturdy fimbriae (ext = external surface, int = internal surface), and basal portion in girdle view (C) D, E internal views of apical and basal poles, respectively, of same valve with valvocopula, showing opposite asymmetry of the notches (arrows) F basal portion of valve with attached girdle bands, showing how the copula fimbriae fit over the valvocopula at poles (arrow) G apical portion of copula showing poration. Scale bars: 5 µm.

(designated here). Specimen at 14.9 mm E and 9.6 mm S of the mark on slide 2920, deposited at ANSP, accession # ANSP-GC20090. Fig. 7A–C.

Phycobank http://phycobank.org/103236.

Bikar Atoll, Marshall Islands, 12.223°N, 170.096°E, on seaweed filaments attached to coral from a farmer fish territory in the lagoon. Collection number BA-5, October 2019. Andrew McInnis leg.

Named for Bikar Atoll, Republic of the Marshall Islands, where it was collected.

The apparent absence of a bifacial annulus is unique among the Synedrosphenia species described here, where there is usually at least a hyaline line visible on the valve face or at the face-mantle margin. There is, however, a misalignment of striae evident in places along the valve–mantle junction (Fig. 7D, E), as observed in the other bifacial-annulus taxa described here, and hence no reason to suppose the growth of the valve proceeds differently. We hypothesize that there is an effective annulus present.

Extremely long heteropolar cells, differing from other species in the cuneate shape in valve and girdle views.

Frustules heteropolar, tapering uniformly in both valve and girdle view (Figs 9D, 10A, B), attached to seaweed substrata by mucilage stalks; plastids numerous, lenticular to oval (Fig. 9A, B). Valve margins parallel near basal pole, 14 µm wide, widening evenly to 27 µm wide just before the cuneate obtuse or slightly rostrate apical pole, length 600–735 µm (Fig. 9A–D). Striae parallel except radiate near apical pole, 19 in 10 µm near the apical pole, 16–17 near the basal pole (Fig. 9E–H). Annulus, evident even in living specimens (Fig. 9A), nearly halfway between centerline and valve margin (Fig. 9B–H), underlain by a longitudinal costa except at apical pole (Fig. 9G, H). Valve border with a rim along its length and shallow pseudosepta at each pole (Fig. 9G, H), the latter matched by extensive development of the valvocopula. In girdle view, three bands evident, all fimbriate (Fig. 10A–C, F). Valvocopula bearing a row of pores at the edge of the pars interior and five rows of pores on the exterior near the apical pole, reduced to two near the basal pole, the pores in a decussate pattern, 27 in 10 µm, the edge of the pars interior bearing short fimbriae near the apical pole, longer elsewhere (Fig. 10D–F). The pars interior of the valvocopula at the poles formed a deep shelf with an irregular surface (Fig. 10D, E), creating a notch on one side and a shallower, longer gap on the other (Fig. 10A, B); notches were on opposite sides of both the valvocopula itself and when comparing epitheca and hypotheca (Fig. 10A, B arrows). The line of pores along the edge of pars exterior moved to inner edge of the gap and became slitlike (Fig. 10G, arrow). Copula (Fig. 10A, B, F, H) wider, again with pores in a decussate pattern, about 10 rows near apical pole diminishing to five at the basal pole, a wide delicate fringe along the edge of the pars interior. The relationship between the first two girdle bands at the poles is shown in Fig. 10I. The pleura (Fig. 10A–C) had a broad apical cap, quickly tapering to a narrow external line with fimbriate pars interior, broadening again somewhat at the basal pole; this band lacked pores.

Figure 9. 

Synedrosphenia licmophoropsis sp. nov. A apical pole of living cell showing plastids and annulus (arrow) (GU44AV-8) B–D holotype valve from GU55B-4 in LM: apical and basal portions showing annulus and entire valve E, F external view of valve, SEM: basal and apical poles, respectively, same scale (GU44Y-13) G, H apical and basal poles, respectively, valve in internal view, SEM, showing longitudinal and transverse costae and pseudosepta (arrows) (GU56A-2). Scale bars: 50 µm (D); 10 µm (A–C, E–G); 5 µm (H).

Figure 10. 

Synedrosphenia licmophoropsis sp. nov., girdle bands A, B frustule in girdle view with thecal elements labeled, respectively on the apical part and the basal pole of the same cell also showing the asymmetrical apical notches in the valvocopula (arrows) (GU55D-3) C small portion near middle of frustule where pleura (pl) is exposed (GU76B-2) D, E basal pole of valvocopulae at 0° tilt with opposite valve in the background and tilted to show complex shape of the pars interior, arrowhead pointing toward notch (GU76B-2 and TK4, respectively) F portions of valvocopula and copula showing fimbriate inner edges (GU55D-3) G valvocopula, apical pole in abvalvar aspect with attached valve, showing elongated pores on inner edge (arrow) (GU44BJ-2) H apical portion of copula showing very long fimbriae at the tip (arrow) (GU55D-3) I relationship between first two girdle bands at basal pole, the long fimbriae of the copula overlapping the valvocopula (GU76B-2). Scale bars: 10 µm (A, B, F, H); 5 µm (C–E, G, I).

(designated here). Specimen at 13.0 mm E and 5.0 mm S of the mark on slide 455, deposited at ANSP accession # ANSP-GC20086. Fig. 9B–D.

Phycobank http://phycobank.org/103237.

“Pete’s Reef” (commercial dive site), Agat Bay, 13.347°N, 144.639°E. Epiphytic on Halimeda at 10 m, collection number GU55B-4, 13 Dec. 2008. C. Lobban and M. Schefter, leg.

Guam: GU44Y-13!, GU44AV-8!, GU54A-B!, GU56A-2!, GU66B-6!, GU76B-2. Federated States of Micronesia: Yap: Y-37-8!; Marshall Islands: Bikar Atoll BA-5!.

Named for its resemblance to certain large Licmophora spp., especially L. attenuata Lobban, Tharngan and Ashworth.

Longer and more evenly tapered, apical pole broadly rounded, striae denser compared to S. gomphonema; valves appearing narrower than S. gomphonema because of the greater length, but the apical poles are equally wide.

Shorter and narrower than S. gomphonema and more finely striated. Girdle bands distinctive: copula with very long internal fimbriae at poles, pleura a large apical cap.

Frustules heteropolar in valve and girdle views (Fig. 11A, F, G) with numerous small plastids (not shown). Valves 196–250 µm long, 18 µm wide near the apical pole, clavate with acutely rounded to weakly rostrate apical poles (Fig. 11A–E). The annulus evident in LM but close to edge of valve face (Fig. 11A, C). Valve surface with weak longitudinal furrows, mantle deeper toward apical pole (ca. 11 vs. 5 areolae deep) (Fig. 11 B, C, F, G). Striae 16 in 10 µm near basal pole, 18–20 in 10 µm near apical pole, parallel except radiate at apical pole (Fig. 11A–E). Pseudosepta present at both poles (Fig. 11D, E); longitudinal costae subtending annulus and transverse costae on vimenes except at apical pole (Fig. 11D, E). Three girdle bands are present (Figs 11F, G, 12E–G). Valvocopula with a row of pores along outer edge of pars interior plus three rows decreasing to one on pars exterior; pars interior with a notched flange at each pole and a fimbriate edge (Fig. 12B). Copula with up to nine rows of pores at apical pole in decussate pattern, decreasing to three near basal pole (Figs 11F, G, 12C, D). Pleurae a pair of polar caps (connecting band not seen), the apical cap relatively massive with small pores and fimbriate (Figs 11F, 12E–G), basal cap smaller, with fewer pores (Fig. 11G arrowhead).

Figure 11. 

Synedrosphenia parva sp. nov. A holotype from Guam in LM, arrow indicates annulus near valve face–mantle junction (GU75A-4) B, C valve in external view (SEM), basal and apical poles, respectively, arrow indicates annulus (GU75A-4) D, E internal views of apical and basal poles, respectively, arrows indicate pseudoseptum (J5) F, G frustule in girdle view, apical and basal portions, respectively, showing the girdle bands including the large apical cap of the pleura, smaller at the basal pole and perhaps not connected (arrowhead in G indicates the apparent end of the pleura); arrows on F, G point to polar notches (GU75A-4). Scale bars: 25 µm (A); 10 µm (B, C, F, G); 5 µm (D, E).

Figure 12. 

Synedrosphenia parva sp. nov., cont. All GU75A-4 A, B valvocopula showing apical internal side from abvalvar position, and portion of middle from advalvar side, respectively, showing row of pores along base of pars interior and fimbriae C internal view of apical pole with valvocopula in situ and the copula, broken in the middle, covering the valvocopula around the apical pole and left side D basal pole of same specimen, again showing the long fimbriae overlapping the valvocopula E, F frustules tilted to show polar (apical) architecture of, respectively a recently divided cell, where the pleura is in place between the copulae of the two cingula, and a non-dividing cell G detail of a pleura loosened from its position and showing some of the fimbriae (still tucked under the copula at top of image). Scale bars: 10 µm (A); 5 µm (B, D–F); 2.5 µm (C, D, G).

(designated here). Specimen at 15.3 mm E and 12.7 mm S of the mark on slide 2326, deposited at ANSP accession # ANSP-GC20088. Fig. 11A.

Phycobank http://phycobank.org/103238.

Agat Reef behind Anae I., Agat Bay, 13.357°N, 144.645°E. Epiphytic on seaweed at low tide line, collection number GU75A-4, 6 May 2017. C. Lobban and M. Schefter leg.

F.S.M.: Chuuk, TK4!; Marshall Islands. Jaluit Atoll, J5!.

Named for its small size within the genus.

Long, straight valves with isopolar, bluntly rounded poles, differing from Synedrosphenia (Ardissonea) crystallina in the marginal annulus, shape of pole, and poration on girdle bands, and from Synedrosphenia (Ardissonea) fulgens in the notch and poration of the valvocopula.

Valves linear, slightly wider in the middle, isopolar with bluntly rounded poles, length 406–430 µm, width 13–16 µm, striae parallel except at pole, 16–18 in 10 µm, areolae slightly elongated in apical axis (Fig. 13A–D). Valve face longitudinally depressed along midline (Fig. 13F, I, K). Annulus detectable externally as a narrow space between areolae around pole and along edge of valve face (Fig. 13D arrows); internally, the end is seen between the areolae at the pole and can be traced around the same as externally (Fig. 13H, L arrows). There are no longitudinal costae (Fig. 13E, J arrow) and transverse costae underlie the vimines as continuous costae from one marginal rim to the other (Fig. 13J). Valvocopula (Fig. 13E–J) lacking external areolae, pores along edge of pars interior have costae between them on the pars interior, appearing to be slits (compare Fig. 13H, J) and the line deflects around the asymmetric sculpting at pole (Fig. 13H). A discrete notch at pole of valvocopula (Fig. 13F, G, I); fimbriae not observed. Copula (Fig. 13E, F) broader with a line along interior–exterior boundary dividing internal bifurcated fimbriae from external part perforated by long slits (rimae) that sometimes continued to the abvalvar edge; perforations discontinued around pole. Pleura glimpsed in Fig. 13K, apparently apical caps joined by very narrow perforated band lacking fimbriae.

Figure 13. 

Synedrosphenia recta sp. nov. Chuuk TK28 except as noted A, C holotype and details of pole at two focal planes, showing valve face and valvocopula B, D–F specimen in SEM with details of pole at 0° tilt (D), arrows showing position of annulus, and 60° tilted views of central portion (E) showing copula and opposite pole (F) showing copula and valvocopula with apical notch (arrow) G, H internal view of a pole with valve and valvocopula at 60° tilt, showing apical notch (arrow), and at 0° tilt, showing apical area without transapical costae; arrows show inferred position of annulus as in D and absence of longitudinal costae I polar view of valve with valvocopula, showing apical notch J broken valve showing continuous transverse costae (arrow) and pores on pars interior of valvocopula (arrowheads) K specimen from Guam (GU76B-4), showing fragments of very narrow pleura (pl, arrows) L specimen from Jaluit (J5), pole of valve without valvocopula, showing continuous rim and absence of longitudinal costae; two-way arrow marks position of annulus, as in D, H. Scale bars: 50 µm (A, B); 10 µm (C); 5 µm (D–L).

(designated here). Specimen at 14.3 mm E and 5.7 mm S of the larger mark on slide 154, deposited at ANSP accession # ANSP-GC20113. Fig. 13A, C.

Phycobank http://phycobank.org/103239.

Federated States of Micronesia: Chuuk: Moch Islet at Eastern Passage of the barrier reef (7°30'50.7"N, 151°57'59.8"E), epiphytic on filamentous seaweeds in farmer fish territory, collection number TK28, 30 May 1991. C.S. Lobban and M. Schefter leg.

Guam: GU76B-2!. Marshall Islands: Jaluit, J5!.

L. rectus, straight. Named for its parallel sides and isopolarity.

This species resembles two former Ardissonea species which we are separating into different genera. The complex polar architecture places it in Synedrosphenia, within which it is differentiated from S. (Ardissonea) crystallina by the marginal annulus, bluntly rounded poles, plain valvocopula and slits on the copula. The shape of the poles and the marginal annulus resemble Ardissoneopsis fulgicans, and in LM of Chuuk samples S. recta was distinguishable only by length, the A. fulgicans specimens being only 300 µm long. We first noticed it when we found a specimen, apparently of A. fulgicans, with a valvocopula pole evidently of the Synedrosphenia type (Fig. 13H). It was necessary to tilt specimens to see girdle band characters.

Specimens from Bikar Atoll (not illustrated) with longer (to 583 µm) but narrower (7 µm) valves, weakly inflated at the poles and in the middle, were structurally indistinguishable from the Chuuk specimens on which the species is defined, including the lack of longitudinal costae. Without further evidence, we cannot decide whether to assign this to a formal varietal status, describe it as a separate species, or leave it within the scope of S. recta. We mention it here to underline the point that the present study does not exhaust the biodiversity of these genera in Micronesia.

Peragallo and Peragallo 1897–1908, p. 311, pl. 79, fig. 5; Hustedt 1931–1959, p. 228, fig. 717a; Navarro 1982, p. 260, figs 64, 65; Poulin et al. 1986, figs 31, 32; Witkowski et al. 2000, p. 44, pl. 31, figs 9–11; Hein et al. 2008, p. 23, pl. 8: 1, 2).

Kanjer et al. (2021) reported the ultrastructure of Greville’s type material of this species, collected at Mull, Scotland, and clearly showed a pseudoseptum and sculpted apices on the valvocopula; no apical notch was observed. That architecture is not visible in LM and so we can only assume that collections reported from Atlantic and Mediterranean Europe are the same until they can be examined. The species as traditionally understood is described as follows: Valves narrow, linear except slightly wider in the middle, 170–450 µm long, 10–15 µm wide, striae 12–14 in 10 µm, offset slightly where they meet such that a central line (“pseudoraphe”) is distinct but very narrow; longitudinal costae very near to the valve edge and normally difficult to see (Hustedt 1931–1959). Kanjer et al. (2021) show an undulation in the annulus near the middle of the valves in holotype material, a feature not reported elsewhere; they reported a stria density of 15–16 in 10 µm. Poulin et al. (1986, figs 31, 32) showed a valve without pseudoseptum, i.e., of the Ardissoneopsis type, with transapical costae on the virgae except at the poles, and the annulus near the valve-mantle junction marked externally by a gap in the areolae and internally by a longitudinal costa on each side. SEMs of var. mediterranea, with 17 striae in 10 µm, in Güttinger (1989), include an oblique view suggesting that the annulus is not internally thickened. Navarro (1982) gave dimensions of 554 µm long by 13.5 µm wide, 14–15 striae in 10 µm. Hein et al. (2008) showed “Ardissonea cf. fulgens” with dimensions of 123–186 µm long by 6.5 µm wide, striae 20 in 10 µm—i.e., smaller and more finely striated than classical descriptions, and they noted that their counts of striae from images in Witkowski et al. (2000) showed stria densities of 19–22 in 10 µm.

For the reasons given below for separating single-walled Ardissonea taxa, it cannot remain in Ardissonea sensu stricto. If this species is confirmed to lack the apical notch, its pseudoseptum and sculpted valvocopula are sufficiently strong characters to place it in Synedrosphenia; it certainly does not belong in Ardissoneopsis, proposed below, which lacks those characters, and we therefore must describe our fulgens-like taxa as new species and propose a new combination of Synedrosphenia fulgens for Greville’s species.

Differing from congeners in the straight outline, only weakly inflated at the center.

Valves 205–320 µm long, 9–15 µm wide, usually slightly widened in the middle and bluntly rounded at poles (Fig. 14A–F); 17–19 parallel striae in 10 µm. Cells attached by one pole to sturdy mucilage stalks (not shown). Annulus along valve–margin junction and not visible in LM, underlain by longitudinal costae (Fig. 14C, D, F, G); sternum absent but striae often out of alignment at the midline (Fig. 14B, H); often spines on poles (Fig. 14D, I). Valve rims straight (i.e., lacking a pseudoseptum) and valvocopula simple, therefore no apical groove (Fig. 14E, F); transverse costae on the mantle thinning toward the margin (Fig. 14G; contrast Fig. 13J). Transverse costae on most vimenes but absent from a relatively large area at the poles (compared to Synedrosphenia recta, Fig. 13H) (Fig. 14F, H). Three girdle bands were present (Fig. 14E, I, J). Valvocopula (Fig. 14E, H, J) with generally two rows of pores on pars exterior; pars interior with a single row along outer edge and a fimbriate inner edge. Copula (Fig. 14D, E, I) with multiple rows of pores forming a decussate pattern, and a fimbriate advalvar margin. Pleura barely visible as a narrow cap at each end, possibly connected, apparently fimbriate at the poles (Fig. 14E, I).

Figures 14. 

Ardissoneopsis fulgicans sp. nov. A, B valve in LM showing shape and striation (TK28) C pole of frustule from acid cleaned material in SEM, showing annulus (double-headed arrow) (J5) D, E poles of frustules in whole mounts, attached at opposite ends, showing girdle bands and apical spines (GU7R) F, G internal views of valve pole and central portion, showing the absence of pseudoseptum at pole and presence of longitudinal costae (arrows) (GU44N-A) H pole of valve with valvocopula, showing start of transverse costae (arrow) (contrast with pole of Synedrosphenia recta Fig. 13H); arrowhead indicates edge of fimbriate copula (J5) I, J poles of frustules showing fimbriae on copula and valvocopula, respectively (J5). Scale bars: 25 µm (A); 10 µm (D); 5 µm (B, C, E–J).

(designated here). Slide 449, multiple specimens present. Slide deposited at ANSP, accession # ANSP-GC20111. Representative specimen published in Lobban et al. 2012, Micronesica 43: pl. 16, figs 4, 5.

Phycobank http://phycobank.org/103241.

Guam: Apra Harbor, GabGab reef. 13.443°N, 144.643°E, sparse filamentous algal turf in farmer fish territory (Plectroglyphidodon lacrymans), depth ca. 5 m., collection number GU44Y-13, 10 May 2009. C. Lobban, M. Schefter leg.

Guam: GU7R!, GU44Z-15!, GU44L!, GU44N-A!, GU44AC-3!, GU44BJ-4! (inter alia); Federated States of Micronesia: Chuuk: TK28!; Marshall Islands: Jaluit J5!.

Adjective (Latin), fulgens (shiny) + -icans (“indicates... resemblance sometimes so close as to be almost identical” – Stearn 1973: 309).

In our region, this species is hard to positively identify in LM from the new species Synedrosphenia recta described above, and some other species so far only glimpsed but differs in (1) having simple apical structure unlike Synedrosphenia spp.; (2) the presence of two or more rows of pores on the valvocopula exterior. Lobban et al. (2012) previously identified this species as Ardissonea fulgens on the basis of literature but Kanjer et al.’s (2021) surprising finding about the type material (see above) forced the reevaluation.

Differentiated from congeners in the straight valve with inflated center and apices, and valve-appressed colony formation.

Cells valve-appressed to form flat colonies from sturdy mucilage pads, cells toward the outside increasingly curved in the apical axis (Fig. 15A–D). Nucleus in widest part of the cell and appressed to one side, numerous lenticular plastids (Fig. 15B). Valves very long and narrow, inflated at the middle and poles (Fig. 15E–G); frustule also inflated in the middle in girdle view because of deeper mantle and wider girdle bands (Fig. 15C vs D). Length 560–900 µm, width at center 9–12 µm, poles 7–10 µm, 5 µm in between; striae 18 in 10 µm (Figs 15F, G, 16A–C). Annulus along junction of valve face and mantle except at poles, where it is further back (Fig. 16B, C); some thickening under annulus but not as thick as transverse costae (Fig. 16E). Striae parallel except radiate at poles (Fig. 16B, C). Internally, costae on most virgae except near poles (Fig. 16C, E, F). Spines absent. No pseudosepta (Fig. 16C); transverse costae on the mantle diminishing toward margin (Fig. 16E arrowhead; contrast Fig. 13J). Three girdle bands present (Figs 15D, 16A): fimbriate valvocopula (Fig. 16A, F) with two rows of pores around the poles, decreasing to one toward the basal pole, along with one row along bottom edge of pars interior; fimbriate copula (Fig. 16A, D) with six rows of pores in a decussate pattern, decreasing to four near basal pole; pleura (Fig. 15D) very narrow, pars interior not observed.

Figure 15. 

Ardissoneopsis appressata sp. nov. A, B flabellate colony and detail showing hemispherical nuclei surrounded by plastids and appressed to girdle faces; arrows on B show two of the many walls between cells (GU68H-1) C middle of colony in oblique view, showing inflation where nuclei are located D base of colony, showing parts of six frustules including pleura (pl, arrow) (GU44AP-2) E–G half valve from Yap, acid cleaned, with details of central and polar portions showing shape and stria density (Y42-1). Scale bars: 100 µm (A); 50 µm (E); 25 µm (B); 10 µm (C, F, G).

Figure 16. 

Ardissoneopsis appressata sp. nov., cont. GU44BJ-4 except as noted A girdle view of part of colony showing cells joined valve to valve, and the pattern of pores in valvocopula (VC) and copula (cop) (GU44AE-2) B, C valve pole in external and internal view, respectively showing tip of annulus (arrows) D portion of copula showing fimbriae E portion of valve near center: arrow points along longitudinal thickening below annulus and arrowhead indicates narrowing of transverse costae at margin F portion of frustule in narrow part, showing internal and external aspects and portions of the fimbriate valvocopulae (GU44T-1). Scale bars: 5 µm (A–C, E, F); 2 µm (D).

(designated here). Slide 449, multiple specimens present. Slide deposited at ANSP accession # ANSP-GC20111. Representative specimen published in Lobban et al. 2012, Micronesica 43: pl. 16, figs 6, 7.

Phycobank http://phycobank.org/103242.

Guam: Apra Harbor, GabGab reef. 13.443°N, 144.643°E, sparse filamentous algal turf in farmer fish territory (Plectroglyphidodon lacrymans), depth ca. 5 m., collection number GU44Y-13, 10 May 2009. C. Lobban and M. Schefter leg.

Guam: GU68H-1!, GU44Z-15!, GU44T-1!, GU44BJ-4!, inter alia. Federated States of Micronesia: Yap: Y42-1!; Chuuk: TK28!.

Adjective (L.) appressus, appressed, with reference to the colony formation.

We previously (Lobban et al. 2012) identified this species as Ardissonea fulgens var. gigantea (Lobarzewsky) Rabenhorst, based on literature. Starting from Peragallo and Peragallo (1897–1908), that taxon has been described as extremely long (400 µm to 1 mm), with a broad central portion joined to capitate poles by very narrow linear portions, the striae 13–14 in 10 µm, but not forming distinctive colonies. Cells from Guam matched this description, except for somewhat higher stria density, but adhered valve to valve while still attached to massive mucilaginous stalks, giving colonies a unique form, a characteristic not mentioned in the literature. The variety is distinctive enough by the shape and colony formation to differentiate it from the nominate variety but has been even less studied than A. fulgens.

However, drawings of Synedra gigantea Lobarzewsky (1840, p. 276, pl. 6, fig. a–c) show a highly elongated diatom occurring in valve-appressed clusters, somewhat similar to those seen in Guam, but not showing any bulge in the middle and being apparently very flexible; as far as one can tell, the frustule is uniformly linear in both views, but he stated that the side (i.e., valve) view is 3–4 times narrower and with a wavy outline. This does not well accord with valve views of Ardissonea fulgens var. gigantea, which has never been depicted as wavy but has been shown with a strong central inflation. Lobarzewsky’s drawings look more like Licmophora flucticulata Lobban, Schefter and Ruck (2011), which is wavy and very narrow and occurs in valve-appressed clusters, except that the clusters of that species in girdle view are very obviously tapered. The descriptions of this taxon were carried forward into Rabenhorst (1864: 140) and De Toni (1892: 674) but there is no mention of the valve outline. The comparison of its shape to Toxarium hennedyanum (W. Gregory) Pelletan seems to have begun with Peragallo and Peragallo (1897–1908), who clearly describe the valve shape and stria density for the first time, but show a smooth valve outline. This taxon was said to be frequent in the Mediterranean (Peragallo and Peragallo 1897–1908), yet neither they nor Hustedt (1931–1959) refer to valves sticking together in distinctive fan-shaped clusters. The extreme length is the sole character that could link the acid cleaned frustules so accurately described by the Peragallos to the taxon drawn by Lobarzewski (1840), and that is insufficient, so that the identity of Synedra gigantea is a mystery, while the lack of colony information and the lower stria density leave doubt about how the Guam population is related to any European taxa. Given findings of Kanjer et al. (2021) on the nominate variety, we reject our earlier identification and propose a new species for our material.

Grunow 1867, p. 4; Grunow 1877, p. 167, pl. 193, fig. 8a–c.

Very long, to 850 µm, slender, inflated at the center and poles, undulate in between, striae 19 in 10 µm (20–22 according to De Toni 1892). Synedra undosa has the outline of Toxarium undulatum, but linear striae as in Ardissoneopsis appressata.

Remnant material of Grunow 839-4611 [W catalog # W0127010, Acquisition # W-1901-0004611]. Not found in Micronesian samples.

We have not encountered this in the Guam flora but found several fragments in Grunow’s Honduras gathering that showed internal and external structure, confirming the similarity of structure to the two aforementioned Ardissoneopsis spp. A fragment including the central inflation and one pole suggests a total length of ca. 690 µm (Fig. 17A). Widths were 10–11 µm across the center, 9 µm across the poles and 4–5 µm between; stria density 19–21 in 10 µm. The annulus along valve face–mantle junction at least partially subtended by longitudinal costae (Fig. 17B–E). Transverse costae also evident throughout except near poles (Fig. 17F–H). No pseudoseptum. Valvocopula and copula both with multiple rows of pores in decussate pattern on exterior, one row of interior pores, fimbriate inner margin and lacking sculpted apices (Fig. 17I). Copula wider, with fimbriae commonly bifurcated.

Figure 17. 

Synedra undosa from Grunow’s Honduras material A internal view of half valve, total length would have been ca. 690 µm B external view of fragment of frustule including the central inflation C external view of valve fragment with pole D external view of valve fragment near central area showing the strong undulation E detail of external pole showing annulus (double-headed arrow) and spines F–H internal views of central, near central (cf. D), and polar portions of valve, respectively, showing longitudinal costae (arrows) and transverse costae; transverse costae developing gradually toward left in H. I girdle bands, showing fimbriate valvocopula and copula with glimpses of interior costate surface of valve. Scale bars: 100 µm (A); 15 µm (B, C); 10 µm (D–I).

According to AlgaeBase (Miranda in Guiry and Guiry 2020), S. undosa is currently referred to as Toxarium undosum (Grunow) De Toni, 1892, which De Toni recognized as distinct from T. undulatum. We have not found more recent mention of this species, but it clearly cannot remain in Toxarium. Hustedt (1931–1959, pp 224–225) stated that, while Grunow had made clear the abundance of Synedra undosa in his Honduras material, “one must assume he also included S. (Toxarium) undulata,” because Hustedt had not observed specimens matching Grunow’s drawings in Honduras material he examined. Hustedt concluded that this species requires further examination. Grunow, however, was clear that S. undosa was different from S. undulata and the SEM images here clearly prove him right. On the evidence that it is a species in its own right, we propose below its transfer to Ardissoneopsis.

Differing from A. fulgicans in valves being more slender, slightly wavy outline, lower stria density, and markedly heteropolar frustule in girdle view and from A. undosa by lack of central inflation.

Frustules cuneate in girdle view (Fig. 18C, D, N, O), both valve mantle and width of girdle bands decreasing from apical pole to basal pole; hypothesized to be attached to mucilage pads at the basal pole, but not observed in live or raw material. Valves slender, weakly undulating, slightly inflated in the middle and at poles, slightly heteropolar but poles not consistently distinguishable except for mantle depth (Fig. 18A, B, G, E). Dimensions: 206–431 µm long, 5 µm wide except 7 µm across the middle and poles (Fig. 18A–G). Striae parallel, 10–12 in 10 µm, except radiating at poles, areolae small, circular. The annulus near valve–mantle junction, indicated only in places where striae on mantle are offset from those on valve face (oval on Fig. 18I). There is often also an offset across the midline but no sternum. Several spines occur on both poles. (Fig. 18H, K, N, O). Internally, interstriae are barely thickened, not forming costae, and there are no longitudinal costae on the annulus (Fig. 18L, M). Three girdle bands were present (Fig. 18N–R): valvocopula with a row of pores along the edge of the pars interior and a fimbriate internal margin (Fig. 18Q); two rows of pores occur around basal pole, but become one within 10 µm from base, further out becoming two and then three or more rows (Fig. 18N, O). In the copula, also bearing a fimbriate flange (Fig. 18P, R), pars exterior has numerous pores arranged in a generally decussate pattern but becoming looser near basal pole (Fig. 18N, O). The pleura is very narrow even at the poles (Fig. 18N, O, P).

Figure 18. 

Ardissoneopsis gracilis sp. nov. (GU44BJ-4, except B TK28) A–C three specimens to scale in LM to show size range: valves from Guam (A) and Chuuk (B), frustule from Guam in girdle view (C) showing heteropolarity D frustule in SEM tilted 60°, showing both valve and girdle faces E, F pole and mid-section of holotype G–K external views of valve in SEM with other species adjacent for comparison (GU44BJ-4): index image (G) with locations of details marked, apical pole (H) (shown by depth of mantle), compare stria density with Ardissoneopsis appressata (A. g.); top half of center (I), offset areolae in striae within the oval suggest location of annulus; narrow portion below center (J), compare with scattered areolae in adjacent Toxarium undulatum (T. u.); basal pole (K), note spines on both poles L, M internal aspect near middle and at the apical pole, showing lack of costae N, O girdle view of frustule apical and basal poles, showing taper in mantle and girdle bands P possible piece of pleura (pl?) with fimbriae Q, R fimbriate edges of valvocopula and copula, respectively. Scale bars: 50 µm (A–D, G); 10 µm (E, F, H–K); 5 µm (L–R).

(designated here). Specimen at 11.0 mm E, 2.5 mm S of the mark on slide 1831, deposited at ANSP accession # ANSP-GC20087. Fig. 18E, F.

Phycobank http://phycobank.org/103243.

Guam: Apra Harbor: GabGab reef, 13.443°N, 144.643°E, sparse filamentous algal turf on farmer fish territory (Plectroglyphidodon lacrymans), associated with A. gigantea and Toxarium undulatum, depth ca. 8 m., collection number GU44BJ-4, 8 Feb. 2015. C.S. Lobban and M. Schefter leg.

Guam: Apra Harbor: GU52P-7!, GU52AI-1!. Federated States of Micronesia: Chuuk: TK28!; Yap: Y36-2!. Marshall Islands: Majuro: M1!, Jaluit, J1!.

Adjective (Latin), slender.

Most similar to Ardissoneopsis fulgicans but differing in the wavy margin, width only half that of A. fulgicans, and in having only 10–12 striae vs. 19–20 in 10 µm. Its shape resembles some Toxarium hennedeyanum, which can sometimes be slightly wavy and only weakly inflated in the middle (e.g., Suppl. material 4: Fig. S2A–C) but always has a random pattern of areolae on the valve face. Much less inflated in the middle, much less strongly undulate, and more coarsely striated than Synedra undosa.

Grunow 1877, p. 167, pl. 193, fig. 12a–c; Hustedt 1931–1959, p. 230, fig. 718; Sullivan and Wear 1995, p. 182, figs 9–12.

As described from LM (Hustedt 1931–1959), this taxon is easily distinguished from Ardissonea spp. by the prominent longitudinal costa on the midline and the absence of lateral longitudinal costae (i.e., no observable annulus). There is only one wall layer. Valves linear, usually slightly wider in the middle, 320–700 µm long, 16–20 µm wide, 8–9 striae in 10 µm. Robust transapical costae on each of the virgae. As seen in SEM (Sullivan and Wear 1995), the valve has a single wall, areolae are circular, those at the poles slightly smaller and not organized into striae, elsewhere the striae are framed by the transapical costae. Sullivan and Wear stated that the costae extend from the margin to the median costa, but their fig. 12 shows some costae extending from the median costa and the costae are not consistently thick. Sullivan and Wear reported an absence of spines, polar pore fields and rimoportulae. Girdle bands closed, not more than five (three on the epicingulum): the valvocopula broad with a single row of small, circular pores near the advalvar edge of the pars exterior and a large flange that fits inside the valve mantle; there was said to be short fimbriae along its inner edge but they are not evident in the micrographs. There are additional rows of pores on the valvocopula just around the poles. The valvocopula has a flange that fits around the valve mantle but there is no apical notch. The copula is also broad but with several rows of pores (their fig. 11 shows these loosely organized in straight striae of at least three pores), and there is a narrow pleura (Sullivan and Wear 1995); none of their images show the inner edge of the girdle bands. Although not specifically stated in these descriptions, the frustules are implicitly isopolar. Sullivan and Wear (1995) particularly noted the circular areolae, in contrast to the large oval areolae they saw in Ardissonea formosa. Grunow’s (1877) published drawings (as Synedra crystallina var. bacillaris) do not include details of areolae but unpublished drawings archived in the Grunow drawing collection at W (W1901-5465) include several sketches where the areolae appear to be oval. Grunow’s drawings, like those of later authors, show this species as linear and isopolar, with bluntly rounded poles, but his unpublished girdle view shows a slightly tapered frustule.

We were able to find a few fragments of Synedra crystallina var. bacillaris Grunow in an SEM preparation from Grunow’s Honduras gathering (Fig. 19). The external view (Fig. 19A–C), of a fragment 172 µm long that appeared to reach the slightly inflated middle, was distinguished from Ardissonea formosa, also present on the stub, by the row of pores on the exterior of the valvocopula. The pole was blunt, with small spines (Fig. 19B, arrowheads), and the valve linear, although a little wider in the middle. Both valves had 11 striae in 10 µm, comprising oval areolae, and the small fragment, width 10 µm, showing the interior had the characteristic central longitudinal costa and prominent transapical costae (Fig. 19D). A second frustule fragment (Fig. 19E–G), 174 µm long, showed the single line of pores on the valvocopula were 19 in 10 µm, striae on the copula 18 in 10 µm. The broken tip of this valve showed the transverse costae (Fig. 19G).

Figure 19. 

Putative Synedra crystallina var. bacillaris from Grunow’s Honduras material A–C specimen in external view with valvocopula, identified by the length, the straight sides and blunt pole, stria density (11 in 10 µm), and row of pores in the exterior of the valvocopula (arrows); small spines on apex (arrowheads on B) D fragment of valve, interior view, showing central longitudinal costa and transverse costae E–G fragment of frustule showing valvocopula and copula G showing transverse costae (arrow) and absence of inner wall, arrowhead shows additional pores on valvocopula pole. Scale bars: 25 µm (A, E); 10 µm (B–D, F); 5 µm (G).

Specimens provisionally identified as S. bacillaris were found in samples from across Micronesia but there was a range of stria densities and dimensions. All had oval areolae and many had spines. However, there were few fitting the literature description, even overlooking the shape of the areolae, i.e., those with linear valves, blunt poles and 8–9 striae in 10 µm. Those in Guam were mostly among populations of lanceolate specimens and probably part of them (see next taxon). The small, circular areolae shown by Sullivan and Wear (1995) are certainly different from the oval areolae in our specimens but determining the identities of these specimens relative to one another and to the literature will require much further study.

Lobban et al. 2012, pp. 256–257, pl. 13, figs 1, 2 [as Synedra bacillaris (Grunow) Hustedt].

Differing from Grunowago (Synedra) bacillaris in width and lanceolate outline of valve.

Valves lanceolate, often slightly rostrate, 194–341 µm long, 11–16 µm wide, striae 9–10 in 10 µm (Fig. 20A–D), the striae comprising large oval pores; poles with smaller, circular pores, but not organized into polar pore fields (Figs 20E, 21A). Isopolar but wider in the middle in girdle view (Fig. 18F–H). Two small spines usually present on each pole (Figs 20G–I, 21B). Rim present on the valve border but not extended into a pseudoseptum (Fig. 21A). Valve single-walled (Figs 20J, 21A), internally costate with a distinctive central costa the entire length of valve and thickened vimines (Figs 20J, 21A), no annulus detected either as a break in the striae, or any other longitudinal costae (Fig. 21A). Three girdle bands were present (Fig. 20F–H). Valvocopula (Figs 20I, J, 21A, C) without extended lip but having groove on pars interior that fits rim of valve. A single row of pores on advalvar side of pars exterior, circular except elongated near poles (Figs 20G, H, 21A, C), a short line of pores around poles on pars interior (Figs 20I, 21C). Copula has a row of pores on outer edge of pars interior (Fig. 21A, B, D), often hidden under valvocopula and a well-developed fringe on the pars interior; up to 5 rows of pores on pars exterior (Figs 20G, H, 21B, D). Pleura a very thin fimbriate band, continuous along cell length (Figs 20G, H, 21B, D).

Figure 20. 

Grunowago pacifica sp. nov. A–D LM of specimens from GU44BJ-4 (A–C) and GU44Z-15 (D) D, E holotype specimen F–H frustule in girdle view, showing isopolar frustule wider in the middle and three girdle bands (GU44BJ-4) I external view of pole and advalvar surface of valvocopula, the latter showing a short row of small pores on the apical part of the pars interior (arrowhead) and the crenulated edge of the pars interior (arrow) J internal view of pole and abvalvar surface of valvocopula. Scale bars: 50 µm (A–D, F); 10 µm (E, G–J).

Figure 21. 

Grunowago pacifica sp. nov., cont., all GU44BJ-4, except A = SPN2022-1-4 A valve apex showing continuous rim, broken away at lower right, not expanded into a pseudoseptum B frustule at 40° tilt, showing fimbriate inner margin of copula on the hypotheca (top) and line of pores on pars interior (arrow) C valvocopula, showing internal and external aspects, the pars exterior pores (arrow) separated by ridges on the pars interior, and the presence of pores on the pars interior at the pole (arrowhead) D frustule in girdle view with fimbriate pars interior of pleura exposed (arrow) E frustule in polar view tilted 60°, showing girdle bands. Scale bars: 10 µm (A–D); 5 µm (E).

(designated here). Specimen at 18.3 mm E and 6.4 mm S of the mark on slide 146, deposited at ANSP accession # ANSP-GC20085. Fig. 20D, E.

Phycobank http://phycobank.org/103245.

GabGab reef, Apra Harbor, Guam, 13.443°N, 144.643°E, ca. 1 m depth, collection number GU44Z-15, 20 June 2009. C.S. Lobban and M. Schefter leg. Additional slides from this sample have previously been deposited at California Academy of Sciences (CAS) for other species holotypes, but specimens of G. pacifica are not marked. Slides include CAS accession/slide numbers: 627386/223007 (Perideraion spp.), 627383/223005 (Gato hyalinus); 627409/223023 (Astrosyne radiata); and 627396/223010 (Hanicella moenia).

Guam: GU44L-C!, GU44AI-5! (in culture), GU44AP-8!, GU44BH-5!.

Adjective (Latin) with reference to its presence in the Western Pacific Ocean.

Specimens that we (Lobban et al. 2012) referred to Synedra bacillaris were 180–400 µm long, 14 µm wide, with 9–14 striae in 10 µm. This range of stria density is suspiciously large for Ardissoneaceae and suggests that two or more species are being confounded. Some specimens in GU44BJ-4 population were nearly linear but most likely represent an extreme within G. pacifica rather than an occasional G. bacillaris. Both Hustedt (1931–1959) and Sullivan and Wear (1995) remarked on the ease of identifying this species by the strong central costa, compared to other Ardissonea spp., but as with other taxa where a strong identifying character has masked species diversity (e.g., Cyclophora tenuis – Ashworth et al. 2012, Bleakeleya notata – Lobban and Perez 2016), we suspect that there is hidden diversity within “Synedra bacillaris”. The genetic branches are long between lanceolate samples from Guam (GU44AI-5) and Florida (HK291) (see, below, Fig. 33). For now, we can only describe Grunowago pacifica and deal with the generic placement of that species cluster.

Hustedt 1931–1959, p. 222, 224, fig. 713 (as Synedra hennedyana); Round et al. 1990, p. 422–423; Lobban et al. 2012, p. 260, pl. 17, figs 1–5; Kooistra et al. 2003, fig. 1A–R (as T. undulatum); Hein et al. 2008, p.33, pl. 15, fig. 3; Álvarez-Blanco and Blanco 2014, p. 128, pl. 63, figs 4–6.

Colonial on stout mucilage stalks. Long, narrow valves, usually straight, inflated at the poles and the middle, valve lengths ranging from 300 to >1000 µm (Álvarez-Blanco and Blanco 2014); widths 6–8 µm in the middle, 5–6 µm at poles, and about 2 µm elsewhere; transapical striae very short, 9–11 in 10 µm, with scattered areolae in wider central and polar areas (Hustedt 1931–1959). Lobban et al. (2012, pl. 17, figs 4, 5) illustrated variants with few/no pores in the central part of the valve face. Girdle bands are all closed (Kooistra et al. 2003). The valvocopula has a single row of pores along junction between the pars interior and pars exterior and an asymmetrical, notched shelf that fits against the pseudoseptum. The copula has striae that are either porate or become slit-like with broadly fimbriate margins of the pars interior (compare their fig. 1I, L with our Figs 22J, 23J). The narrow pleura has a single row of pores along the junction between the pars interior and pars exterior.

Guam: GU21AK-11!, GU44AK-4!, GU44BJ-4!. Federated States of Micronesia: Chuuk, TK28!. Marshall Islands: Majuro: M1!; Jaluit: J5!; Bikar: BA2!; inter alia.

Valves 156–334 µm long, usually straight but sometimes curved, 7 µm wide at middle, 4–5 µm at poles, with a single row of areolae on the shallow mantle (Fig. 22H, J, asterisk) and two rows before the scattered areolae (Fig. 22B, D, I), making the short transverse striae 3 areolae long; stria density 10–14 in 10 µm (Fig. 22A, B, D, I, J). In the context of the present analysis, we confirm the presence of an asymmetrical pseudoseptum (Fig. 22E), asymmetrical valvocopula poles with apical notch (Fig. 22F–H), valvocopula finely fimbriate (Fig. 22I), and the copula structure tending toward slits, the striae 28 in 10 µm at the poles (Fig. 22G) increasing to 36 in 10 µm with broadly fimbriate pars interior (Fig. 22J). There is a knuckle-like series of arched slits on the valvocopula pars interior (Fig. 22F), different from the structure in Synedrosphenia (compare with Fig. 8B and Fig. 10D, E, G). Spines absent. We note that the pars exterior of the copula is hyaline around the poles. However, the fine fimbriae on the pars interior of the valvocopula (Fig. 22I) are absent from the specimens in Kooistra et al. (2003 fig. 1J, K). A pleura was present (Fig. 22H), the pars interior also fimbriate (not shown).

Figure 22. 

Toxarium hennedyanum, all from GU44BJ-4 except C GU21AK-11, and I, K culture from GU44AK-4 A LM of valve with typical pattern in central area; 9 stria in 10 µm B SEM of a valve from same sample, 12 striae in 10 µm, with reduced central area C mucilaginous stalks with clusters of cells D internal central area, showing lack of costae E, F internal pole of valve showing asymmetrical pseudoseptum (arrow) and valve with valvocopula showing similar asymmetry (arrow) G pole of frustule in girdle view showing apical groove (arrow) on valvocopula and fimbriae partially exposed on copula H pole of frustule in girdle view showing apical notch (arrow) and the pleura (pl); note single row of areolae on mantle (*) I pole of valvocopula in girdle view, fimbriae absent from the tip J narrow portion of valve showing structure of copula (compare with Fig. 23J) and single row of pores on mantle (*) K pole of copula in girdle view showing long fimbriae. Scale bars: 50 µm (A–C); 10 µm (I); 5 µm (D–K).

Kooistra et al. (2003) show a single row of pores on the mantle and a copula that matches those shown here for T. hennedyanum. They do not state a stria density, but we count 11 in 10 µm, measured from their fig. 1E. There has been a tendency to ignore stria density, reflecting the marginal striae and the domination of the valve face by scattered areolae. Kooistra et al. (2003) had monoclonal cultures in which both hennedyanum-like and undulatum-like cells were present, and they proposed a merger of the two species. The specimens they show had a rippled edge, but not a strongly wavy outline (contrast Poulin et al. 1986; Hein et al. 2008, and our Fig. 23); i.e., a midline along the apical axis is straight, whereas that in T. undulatum is sinusoidal. If the Micronesian specimens shown here are indeed T. hennedyanum and T. undulatum (by no means certain), our results would suggest that the rippled edge seen in the cultures of Kooistra et al. (2003) was a phenotypic expression of T. hennedyanum and was not T. undulatum. We previously noted (Lobban et al. 2012) the significant genetic variation in Guam isolates of T. hennedyanum and T. undulatum reported by Theriot et al. (2010, 2011) and this is even more evident now; however, in reviewing the vouchers, we find no data from specimens attributable to T. undulatum; all the variation shown in Fig. 33 appears to be part of a T. hennedyanum complex.

Bailey 1854, p. 15, plate (1), figs 24, 25; Peragallo and Peragallo 1897–1908, p. 314, pl. 78, fig. 7; Hustedt 1931–1959, p. 222, 224, fig. 714; Güttinger 1991 (both as Synedra undulata); Poulin et al. 1986, figs 33–36; Hein et al. 2008, p. 33, pl. 15, fig. 3; Lobban et al. 2012, p. 260, pl. 17, figs 6–8; Álvarez-Blanco and Blanco 2014, p. 128, pl. 63, figs 4–6.

Toxarium undulatum, the generitype, was said to differ only in the wavy outline of the valve (Hustedt 1931–1959), stria density rarely reported but Peragallo and Peragallo (1897–1908) state 12 in 10 µm. The outline in Bailey’s (1854) plate is shown as undulating with a long wavelength, in Peragallo and Peragallo (1897–1908), with a shorter wavelength, and in Hustedt (1931–1959) the center clearly has a wavy edge but the “horns” are scarcely undulate. Micrographs in recent works (Witkowski et al. 2000; Hein et al. 2008) show distinctly undulate outlines. In the SEMs shown by Poulin et al. (1986) we count 19–21 striae in 10 µm, whereas Güttinger (1991: 2.01.30-10) shows specimens with lengths of 485 and 580 µm, widths 8 µm at center, 5 µm at poles, but with 12 striae in 10 µm. Lobban et al. (2012) reported lengths of 270–400 µm, widths 5–9 at the center, 6 µm at poles, 4 µm in between, with some specimens having virtually no central inflation; no stria density stated but their fig. 7 shows 12–13 striae in 10 µm. T. undulatum has usually been illustrated as straight but curved specimens are shown by Hein et al. (2008) and Lobban et al. (2012). The genus was emended by Poulin et al. (1986), whose SEM images of T. undulatum show an asymmetrical polar pseudoseptum and internal transverse costae “in parts of the valve between the poles and the center and sometimes anastomosing” (also shown in Güttinger 1991). The T. undulatum from Guam (GU44S / HK210 / ECT 3802) used by Ruck et al. (2016) showed very shallow undulations, at least after culture, and additional images of the voucher stub show that it has a single row of areolae on the mantle (Suppl. material 4: Fig. S2A–C), so we would therefore identify it as T. hennedyanum. A similar specimen from wild material is also shown in the Suppl. material 4: Fig. S2D–F.

Guam: GU44X-2!, GU44Z-15!, GU44BJ-4!, inter alia; Federated States of Micronesia: Chuuk, TK28!; Yap, Y36-2!, Y42-3!. Marshall Islands: Majuro, M1!, Jaluit, J5!

Valves straight or commonly curved overall, strongly sinusoidal along the narrow part, the oval central portion with a wavy outline, apical portions straight sided (Fig. 23A, B, F), length 255–326 µm, width 5 µm at poles, 7 µm at the center, 3 µm in between, stria densities 14–17 in 10 µm (Fig. 23C–I). Mantles deep with typically 3–4 areolae in the stria there (Fig. 23H, I, K). Spines absent. Valvocopula plain except for single row of pores along the base of the pars interior, fimbriate edge to pars interior (Fig. 23G), knuckle-like structure at poles, as in T. hennedyanum (Fig. 23K, compare with Fig. 22F). Copula with a regular pattern of small areolae on the pars exterior, forming striae consistently 34 in 10 µm (Fig. 23H–J, L), in which the pars interior, while similar to that of T. hennedyanum near the poles, quickly becomes a fringe of short, narrow fimbriae with a line of triangular pores along the junction with the pars exterior (Fig. 23H). The narrow pleura was largely or entirely obscured (Fig. 23L) (this pole identified as T. undulata by 2+ rows of areolae on the mantle, and pores on the poles of the copula; contrast Fig. 22H); a small exposed portion showed a fimbriate edge (Fig. 23M).

Figure 23. 

Toxarium undulatum (all from Guam, GU44BJ-4) A, B entire valves in LM and SEM, respectively, showing prominent undulation C, D central expanded portion external and internal views, respectively, the latter showing costae E pole, internal view showing asymmetrical pseudoseptum (arrow) F internal and external aspects of valve in the narrow part G valvocopula lying inside narrow part of valve H, I portion of frustules in girdle view, showing multiple rows of pores on mantle, valvocopula with apical notch (arrow), and copula with pores continuing around the pole (arrowhead) J detail of copula, for comparison with Fig. 22J K pole of valvocopula showing arched slits L frustule in girdle view showing pleura M fragment of the pleura, showing fimbriae. Scale bars: 50 µm (A, B); 10 µm (C); 5 µm (D–I, K); 2 µm (J, K, M).

We also documented T. undulatum in Grunow’s Honduras sample (Fig. 24). A whole valve was 700 µm long (Fig. 24A) with long-wavelength undulations. The deep mantle sometimes exhibited longitudinal waves in the areolae (not solely an artefact of the wave in the valve, shown by short additional longitudinal lines of areolae—Fig. 24D, arrows). The striae on the valve face were two areolae long on each side bordering scattered areolae in the inflated center and poles (Fig. 24C, E), internally, the virgae were thickened into costae (Fig. 24C). Valvocopula (Fig. 24C, E–G) with a single line of areolae on the exterior, short fimbriae along the interior margin except at the sculpted poles, and a series of arched slits (Fig. 24F, G; compare Fig. 23K). Copula (Fig. 24C–E, H) wide with coarse fimbriae on the pars interior, forked at the tips, exterior with striae of pores tending to merge into slits, especially on the advalvar side. Fimbriate pleura clearly seen in Fig. 24H.

Figure 24. 

Toxarium undulatum from Grunow’s Honduras material A, B entire valve, 700 µm long, and detail of central portion, showing long-wavelength undulations C portion with the central inflation, showing mantle depth, internal costae, valvocopula and copula (stria density 14 in 10 µm) D frustule in girdle view, showing vertical wave in rows of areolae with inserted arcs (arrows); notice also the different depths of the two mantles (stria density 17 in 10 µm) E portion of valve with copula and valvocopula F, G valvocopula pole, abvalvar and advalvar surfaces, respectively, showing series of arched slits (compare with Fig. 22F) H pole of frustule showing fimbriate pleura and notch in valvocopula. Scale bars: 100 µm (A); 25 µm (B); 10 µm (C–E); 5 µm (F–H).

The specimens from Grunow’s Honduras material are near the length (“about 35m” = 890 µm; see Itaki and Bjørklund 2006) and shape described by Bailey (1854) for specimens from Sargassum in Narragansett Bay. As noted by Hustedt (1931–1959), Grunow (1877) did not mention this species (in the context of presenting new species), but Hustedt says he observed it on Grunow’s slides.

In the Micronesian samples, depths of the mantle, and structure of the copula were different in the two species, so we can assert that the specimens shown here for T. hennedyanum and T. undulatum are different species. The large genetic variation in Toxarium materials we have sequenced (Fig. 33) casts doubt on whether either of them might be identified to authentic Atlantic types, a question highlighted by the Grunow specimens. It similarly raises questions about the number of species there might be in Micronesia. Both questions require much more work to define the range of character states and their combinations, but the oft-repeated claim that the two species differ only in outline is already not supported by morphological evidence. The more important point for the present study is to establish generic characters for comparison to those of the genera in Ardissoneaceae and Climacospheniaceae.

The Toxarium spp. specimens shown here from sample GU44BJ-4 were in a community with the new species Ardissoneopsis gracilis (see above), which has a slightly undulate outline but is distinguished from T. undulatum by the cuneate girdle view, regular striae across the valve face, apical spines, and the decussate pattern of pores on the girdle bands (Fig. 18). Also present were Synedrosphenia gomphonema, S. crystallina, Ardissoneopsis fulgicans, A. appressata, and Grunowago pacifica.

Bailey 1854, p. 353, pl. 1, figs 10, 11; Peragallo and Peragallo 1897–1908, p. 352, pl. 86, figs 2–4; Hustedt 1914, pl. 307, figs 1–4; Ricard 1977, figs 669–677; Montgomery 1978, pl. 114, fig. E–H; Round 1982, figs 1–38 (in part); Round et al. 1990, p. 442.

C. elongata has been described (e.g., by Peragallo and Peragallo 1897–1908 and Hustedt 1931–1959) as identical to C. moniligera Ehrenberg, 1843 except for the valve tapering more abruptly to a stem with parallel sides. Yet Bailey (1854) had specifically distinguished his species from C. moniligera by the finer stria density (without giving numbers) and described a species 330 µm long, with very wide craticular bars (as shown also in Peragallo and Peragallo 1897–1908, pl. 86, fig. 5; Hustedt 1914, pl. 307, figs 1–4; and Round 1982, fig. 3) (Table 5). Peragallo and Peragallo (1897–1908) gave stria densities of 18–21 near the basal pole, 27–>30 near the apical pole for C. elongata versus 16–17 in 10 µm basal and 19–20 in 10 µm apical for C. moniligera but expressed the opinion that there was intergradation between the two species. Hustedt (1931–1959) said that Peragallo and Peragallo had confused their European specimens of C. elongata with C. moniligera and he attempted to resolve the confusion with an original drawing of a cell with a very long, very narrow stem. The drawing (his fig. 626) was based on Samoan specimens he had published in “Schmidt’s Atlas” (Hustedt 1914). Round (1982) attempted to clarify the difference between the two species, not considering the variation within C. elongata, but his drawings of C. elongata show specimens no more than 320 µm long. In recent literature, Álvarez Blanco and Blanco (2014), show short cells similar those in Peragallo and Peragallo (1897–1908), while Navarro and Lobban (2009) reported cells 750–1200 µm long from a Guam sample, similar in shape to those in Hustedt (1931–1959), a range that otherwise occurs only in Hustedt’s report (table in Álvarez Blanco and Blanco 2014: 103). Ultrastructural characters: Apical spines present; costae generally present; frustules have only two girdle bands, both with fimbriate inner margins (Ricard 1987, fig. 677; Montgomery 1978, pl. 114, fig. G; Round 1982).

Guam: GU44Y-13!, GU44U-1B!, GU44BM-4!, GU44BM-7!, GU52X-1!. Federated States of Micronesia: Chuuk, TK4!

Valve clavate, apical part gradually tapering to a narrow stem nearly half the total length of 278–516 µm (Fig. 25A, B); maximum width 30–33 at apical pole, 7–8 µm across stem and expanding slightly to 9 µm across basal pole (Table 5); annulus closed at both poles, gradually tapering from maximum width of 16–17 µm near apical pole (Fig. 25B arrows, D, E). Stria densities 28 in 10 µm near apical pole (Fig. 25E), 22 in 10 µm near basal pole outside the annulus; sparser and more loosely organized inside annulus at basal pole (Fig. 25D, G). Apical spines present (Fig. 25E), pseudoseptum absent (Fig. 25G). Costae present except at basal pole, where they start at margin and extend centripetally, eventually thickening the virgae inside the annulus (Fig. 25G). Valvocopula stria density 19 in 10 µm (Fig. 25E, F), pars interior with comb of long, unbranched fimbriae (Fig. 25C). Craticular bars consistently narrow (1 µm) (Fig. 25B, D, G, H), though sometimes doubled (Fig. 25A), the spaces between them rectangular with rounded corners; connections complex in most of the stem, becoming simple where the valve widened (Fig. 25C, D, G vs Fig. 25B, H). There was a wider space between two of the bars in the middle of the wide part (Fig. 25B, thick arrow); based on our observations on C. elegantissima (below), this is probably the location of the nucleus. Copula with 24 striae in 10 µm (Fig. 25F), pars interior not observed.

Figure 25. 

Climacosphenia elongata, GU44BM-7, except as noted A valve with valvocopula in LM, showing consistently narrow craticular bars, some double (arrowheads) (GU44X-2) B apical part of a valve with valvocopula in SEM, showing the progressive narrowing of the annular ring (series of small arrows) and the wider space between craticular bars where the nucleus resides (thick arrow) C narrow portion of valve with valvocopula showing the fibmbriae D basal pole of valve with valvocopula, showing the scattered pattern of areolae inside the annulus gradually becoming regular striae, development of costae (arrow), and complex unions in the craticular bars E external view of apical pole showing annulus (double-headed arrow) and spines F frustule in girdle view showing the two girdle bands G, H valvocopula near basal pole and in tapering part at top of “stem,” respectively, showing complex versus simple unions in the craticular bars (TK4). Scale bars: 100 µm (A); 50 µm (B); 10 µm (C–H).

The shape and morphometrics accord adequately with the literature on C. elongata, the narrow craticular bars, especially in the stem, differing from the sturdy bars and oval spaces of C. moniligera, and from the very long-stemmed specimens depicted by Hustedt (1931–1959, p. 89, fig. 626). Based on the available evidence, we accept the hypothesis that the specimens shown in Fig. 25 are Bailey’s species.

?Hustedt 1914 in Schmidt et al. 1874–1959, pl. 308, figs 5–10; ?Hustedt 1931–1959, fig. 626; Navarro and Lobban 2009, p. 136, figs 64, 65 (all as C. elongata Bailey).

Differing from C. elongata in the greater length, especially in the stem, and narrower, linear apical portion, and from C. truncata Hustedt ex Simonsen in the shape of the wide part of the valve.

Cells attached in small groups to stout, branched mucilage stalks (Fig. 26A, E), at least 110 µm wide at the base and up to 2 mm long. Frustule generally deeper than wide, especially where stem first narrows below the apical pole, ratio there about 15 µm deep to 5 µm wide (Fig. 27A). Nucleus situated between two more-widely spaced craticular bars about 120 µm from apical pole (Fig. 26A, D); plastids lenticular. Valves 750–1305 µm long, linear toward apical pole, 22–24 µm wide, then tapering to a long linear stem, 5 µm wide, expanding to 10 µm at the pole (Figs 26A–C, 27A). Stria density 27–28 in 10 µm through most of the valve but 18–21 in 10 µm near basal pole, sparser and more scattered inside annulus near basal pole (Fig. 27D, E, G). There was a crescent of scattered areolae at top of mantle at apical pole (Figs 27D, G, 28A) (noticed in Climacosphenia spp. by Round 1982: figs 15, 16, 25). Annulus apparently open at basal pole, sides ±parallel in the wide area, 8.3 µm apart, in the stem 2.3 µm apart, expanded to 5 µm at the basal pole (Fig. 27C–G). Two or more stout spines on external apical pole (Figs 27D, 28A), shallow transapical costae throughout except near basal pole (Fig. 27F, G). Pseudoseptum absent (Fig. 27F, G). Two girdle bands (Fig. 28A): valvocopula (Figs 26B, F, 27B, C, F, I, 28A–C) with fimbriate inner edge (Fig. 28B), stria density 19 in 10 µm (Fig. 28A, B) but increasing around foot pole, where there was also a row of pores on pars interior (Fig. 27I). Craticular bars widely spaced in wide part of the cell, with widest space corresponding to the location of the nucleus (Figs 26B, 27B); in the stem becoming much closer together (Figs 26B, 28C), often paired with the two bars apparently growing from opposite sides (Fig. 28C). In one specimen from culture, we observed porous bands of silica around several craticular bars near the apical pole (Fig. 28D). Copula fimbriate, more densely striated than the valvocopula but less than the valve, 22 in 10 µm (Fig. 28A, E). A search of abundant girdle views in whole mounts showed no sign of a pleura.

Figure 26. 

Climacosphenia elegantissima sp. nov., (GU52AI-1 except B from GU52U-2) A, D living cell, showing extreme length and location of nucleus (arrow) B acid-cleaned complete valvocopula, emphasizing the very long, narrow stem C portion of colony, showing cells attached to mucilage stalk; the two cells to right of middle are 1300 µm long E detail of mucilage stalk with bases of attached cells. Scale bars: 250 µm (A–C); 50 µm (D, E).

Figure 27. 

Climacosphenia elegantissima sp. nov., cont. GU52AI-1, except GU52U-2 (B) and GU52X-1 (G, H) A whole mount of colony in SEM, showing contrasting width versus depth of frustule in the stem (arrows at approximately same distance from apical poles) B portion of holotype in LM; although specimen is broken in two places, the basal pole of the valvocopula is also present, total length ca. 835 µm C apical pole of valve and valvocopula in LM, showing parallel sides of annulus and some misaligned unions in the craticular bars D SEM of external valve surface at apical pole, showing annulus (double-headed arrow) continuing around apical pole, two spines, and crescent of scattered areolae at top of mantle (arrow) E external valve surface at basal pole, showing variation in areola density and alignment within the annulus, apparent discontinuity of annulus at pole, and width of basal pole relative to stem (cf. H at same scale) F internal aspect of basal pole of valve and valvocopula, showing absence of pseudoseptum (arrow) and associated structure in valvocopula G, H internal aspect of valve at apical pole, showing crescent of scattered areolae (arrow) and in the narrow stem, respectively I oblique view of basal pole with valve and valvocopula, showing increase in areola density on the valvocopula around the pole (arrow) and short row of pores on pars interior (arrowhead). Scale bars: 200 µm (A); 50 µm (B); 10 µm (C–H); 5 µm (I).

Figure 28. 

Climacosphenia elegantissima sp. nov., cont. GU52U-2 (A), GU52X-1 (B, C), GU44AI-5 culture (D), GU52AI-1 (E) A whole mount of frustule apical pole in girdle view, showing two girdle bands, patch of irregular areolae on the valve mantle (arrow), spines (arrowheads) B part of valvocopula broken away and showing a solid circular cross-section of the craticular bar (arrowhead) and well-developed fimbriae (arrow) C portion of valvocopula from stem, showing double craticular bars, ingrowths from opposite sides D apical pole with valvocopula showing porous bands of silica around several craticular bars E detail of copula showing stria density and fimbriate margin on pars interior. Scale bars: 10 µm (A, D, E); 5 µm (B, C).

(designated here). Specimen at 16.1 mm E, 12.8 mm S of the mark on slide 1861; deposited at Academy of Natural Sciences, Drexel University, Philadelphia, accession number ANSP GC20108. Fig. 27B.

Phycobank http://phycobank.org/103246.

Guam: Apra Harbor, Scuba Beach, 13.464°N, 144.656°E, epiphytic on filamentous red algae in farmer fish territory, collection number GU52U-2, 10 May 2015. C.S. Lobban and M. Schefter leg.

GU44AI-5! (culture), GU44BM-7!, GU52G-B!, GU52X-1!, GU52Y-3B!, GU52AI-1!.

Superlative of elegans, with reference to the slender appearance of the extremely long cells.

The width of the apical pole and especially the distance between the annular lines are narrower than in C. elongata (Table 5) and the stem is also narrower, though the basal pole is inflated and slightly wider than C. elongata. Hustedt’s (1914) drawings of C. elongata have the greatly extended stems that are present in our new species, but the apical portions of his cells are generally elliptical rather than linear. However, the valvocopula (Hustedt 1914, pl. 308, fig. 6) is notable in having parallel sides as far as the large space (i.e., where the nucleus would have been), so it is possible they represent C. elegantissima. Climacosphenia truncata from Borneo is also illustrated there (pl. 308, figs 1–4); it also has a very long stem but possesses an essentially triangular blade with a bluntly rounded apical pole. C. elegantissima is common as an epiphyte on filamentous seaweeds in Guam farmer fish territories and such habitats around the western Pacific/ IndoPacific may yield new material of C. truncata and other Climacosphenia spp.

Round (1982) showed porous bands of silica on craticular bars near the basal pole of both species only found in Hawaiian material. We saw them only once on apical bars in C. elegantissima. Their distribution and function are unknown.

Mann 1925, p. 59, pl. 12, fig. 4.

Cells tapering uniformly and strongly curved, the septa “delicate,” very narrow, “and showing at the middle either obscurely or not at all the break or sutural division common to specimens of this genus.” Length 414 µm, width at apical pole 28 µm, stria density not specified.

GUAM: GU52U-2!, GU52AH!, GU44Z-15!. F.S.M.: Chuuk: TK28!.

Specimens fitting this description have been found in Guam and Chuuk, often together with C. elegantissima. Colonies on branched mucilaginous stalks, the nucleus near the apical pole between two of the widely spaced craticular bars (Fig. 29A). Length 390–612 µm, maximum width 25–26 µm near apical pole, 8–10 µm across basal pole (Fig. 29A, B). Stria densities outside the annulus 21 in 10 µm in lower part, 29 in 10 µm at apical pole; striae within annulus at basal pole about 16 in 10 µm, areolae more, or less aligned (Fig. 29C–E vs Fig. 30A). Maximum distance across annulus 10 µm (Figs 29B, D, 30A). While annulus appears discontinuous in SEM, phase contrast suggests continuity (Fig. 29C). Valves delicate except at basal pole, apical striae hard to resolve in LM even with phase contrast (Fig. 29C, E), costae not developed on either vimines or annulus, except near basal pole (Fig. 29D). Two spines on apical pole of valve (Fig. 30A, D). Two girdle bands present, both broad and with regular striae, but at different densities, valvocopula 20 in 10 µm, copula 24 in 10 µm (Fig. 30D). Valvocopulae fimbriate with narrow, widely spaced craticular bars, unions all seamless (Fig. 30E–G).

Figure 29. 

Climacosphenia scimiter, all from GU52X-1 A colony of living cells on branched mucilage stalk B valve and valvocopula of cleaned material, LM-DIC, showing consistently narrow craticular bars C, E valve in phase contrast LM, showing more strongly silicified basal pole in C and weakly silicified apical portion in E, along with difference in stria density; note appearance of annulus at basal pole (arrow, C) D basal pole in SEM, oblique view, showing shallow mantle and very weak costae and apparently discontinuous annulus. Scale bars: 50 µm (A, B); 10 µm (C–E).

Figure 30. 

Climacosphenia scimiter, cont. All GU52X-1 except D, GU52U-2 A apical pole of valve, exterior view, showing stria density and spines B detail of valve internal aspect, showing absence of costae C detail of external valve face at basal pole, showing more scattered areolae inside annulus D whole mount of frustule, apical pole, showing spines and girdle bands E–G valvocopulae showing consistently seamless craticular bars. Scale bars: 100 µm (E); 10 µm (A, C, D, F, G); 5 µm (B).

Observations are completely in accord with Mann’s (1925) description of specimens from the Philippines (Mann noted that data on the locations of the dredge samples were lost). Given also that this species was discovered not far from Micronesia, we are confident in the identification. We cannot accept that this is merely a curved C. moniligera, as suggested by Round (1982), because of the great difference in septum characters and differences in stria densities. Whether there exist straight versions of this species, or curved C. moniligera populations, remain open questions.

Differing from C. moniligera in apical stria density and delicate craticular bars throughout, seamless except for complex unions in the most basal 1–4 bars and from C. scimiter in straight outline, presence of complex unions, and cell width.

Valves straight, gradually tapering from apical pole almost to basal pole (Fig. 31A–C), only a short basal part with parallel sides. Length 390–530 µm, width 29–35 µm across apical pole (measured on valvocopula; total valve width including mantles 50 µm), 10–12 µm across basal pole at last craticular bar (Fig. 31A–G). Annulus narrower at apical pole (Fig. 31C–E), widest 15 µm, steadily tapering to 4 µm, apparently open at basal pole (Fig. 31E). Stria densities 18–20 in 10 µm in lower part of the periphery, 28–29 in 10 µm in periphery at apical pole, about 16 in 10 µm in middle part above basal pole (Fig. 31E). Spines present on apical pole and a small patch of irregular areolae (Fig. 31D). Costae apparently poorly developed. Valvocopula fimbriate with narrow, widely spaced craticular bars that have seamless unions except for the most basal 1–4 (Fig. 31B, F); a row of pores on pars interior just around basal pole (Fig. 31F). Copula not positively identified.

Figure 31. 

Climacosphenia soulonalis sp. nov. All TK4 A–C holotype valve with valvocopula, entire, basal pole and apical pole, respectively, showing seamless craticular bars except near basal pole; arrowheads on B show complex unions D external valve apical pole showing irregular patch of areolae (arrow), spines, and narrowing of the annulus at apical pole E internal aspects of basal and apical poles, showing lack of costae (contrast costae in the piece of Synedrosphenia crystallina to the right) F, G valvocopula with two complex unions at the basal pole (arrowheads, F) and showing the row of pores on the pars interior around the basal pole (arrow). Scale bars: 100 µm (A); 10 µm (B–G).

(designated here). Specimen at 17.8 E, 10.9 mm S of the mark on slide 153; deposited at ANSP, accession number GC20109. Fig. 31A–C.

Phycobank http://phycobank.org/103247.

Federated States of Micronesia: Chuuk: Northeast Pass into Chuuk Lagoon, 7.514°N, 151.967°E, on algal turf from farmer fish territory, lee side of Moch I., collection number TK4!, 30 May 1991. C.S. Lobban and M. Schefter leg.

Chuuk: TK28!, exposed reef, ca. 6 m deep, southeast corner of Northeast Passage.

Belonging to Sou-lon, “the Chuukese god of ocean depths and storms, equivalent, perhaps to Neptune” (W.M. Peck 1992, Chuukese Testament. Storyboard: A Journal of Pacific Imagery 2: 44).

Valves resemble C. moniligera in size and stria densities (Table 5) but differ in the valve shape and the narrow and mostly seamless craticular bars are unlike the massive septum with complex unions in the bars reported for C. moniligera (Peragallo and Peragallo 1897–1908; Hustedt 1931–1959; Round 1982).