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Four new species from the diatom (Bacillariophyceae) genus Adlafia Moser, Lange-Bertalot & Metzeltin from waterbodies of Vietnam
expand article infoAnton M. Glushchenko, John Patrick Kociolek§|, Irina V. Kuznetsova, Maxim S. Kulikovskiy
‡ K. A. Timiryazev Institute of Plant Physiology RAS, Moscow, Russia
§ Museum of Natural History, Boulder, United States of America
| University of Colorado, Boulder, United States of America
Open Access

Abstract

Four species of the diatom genus Adlafia were found from waterbodies of Vietnam and described as new to science. Their formal descriptions are presented herein and they are illustrated by light and scanning electron micrographs. These new species are: A. lamdongiensis Glushch., Kulik. & Kociolek, sp. nov., A. babeiensis Glushch., Kulik. & Kociolek, sp. nov., A. vietnamensis Glushch., Kulik. & Kociolek, sp. nov. and A. dauiensis Glushch., Kulik. & Kociolek, sp. nov. These species are then compared to other similar taxa. Our new findings add to the number of species in this interesting genus and contribute to our understanding of the unique diatom flora found in Vietnam.

Keywords

Adlafia, diatoms, morphology, new species, Southeast Asia, Vietnam

Introduction

The genus Adlafia was proposed by Moser et al. (Moser et al. 1998). According to the original description, the genus is overwhelmingly represented by small-cell species (less than 25 µm in length). The raphe is naviculoid; external distal ends are smoothly bent and slightly extend to the mantle externally while the external proximal ones are drop-shaped, slightly bent to the opposite side from the distal ends (Kulikovskiy et al. 2016). On the inside, the raphe is located on a raised sternum, the distal ends with small helictoglossae, the proximal ends are straight and bent to one side (Morales and Le 2005). A distinctive feature of the genus is the presence of large, often square areolae, closed externally with a hymen and a continuous silica layer (Moser et al. 1998; Lange-Bertalot 2001). Species of the genus are distinguished from those in the genus Kobayasiella Lange-Bertalot in Lange-Bertalot and Genkal (1999) by lacking an “umbilicus”, a deflection or nick in the raphe system on the exterior. Currently, the genus belongs to taxa with an unclear taxonomic position (incertae sedis). Molecular studies of the genus require the involvement of more strains (Kulikovskiy et al. 2016).

The genus includes 27 species and infraspecific taxa (Guiry and Guiry 2020). Species of the genus are distributed around the world. Most species are aerophilous, being found mainly on mosses, but others prefer oligotrophic streams and lakes with a slightly higher or lower pH value, but are rare in large rivers (Spaulding and Edlund 2009; Kulikovskiy et al. 2016; Cantonati et al. 2017). Species are also known from fossil sediments (Lange-Bertalot and Metzeltin 1996; Benson and Kociolek 2012).

Southeast Asia is a floristically interesting region, from which many new genera and species of centric and pennate diatoms have been described recently (see Gusev and Kulikovskiy 2014; Glushchenko et al. 2016, 2017, 2018, 2019; Kapustin et al. 2017, 2019; Liu et al. 2018; Kulikovskiy et al. 2019, 2020; Rybak et al. 2019). Several Adlafia species have been recorded previously from Southeast Asia. In Indonesia, for example, Adlafia bryophila (J. Petersen) Lange-Bertalot in Moser et al. 1998 and Adlafia minuscula (Grunow) Lange-Bertalot in Lange-Bertalot and Genkal 1999 have been reported (Bramburger et al. 2004). Adlafia sinensis Liu & Williams in Liu et al. 2017 was described from south-central China. They also provide a comparison of many Adlafia species. In Vietnam, Adlafia minuscula var. muralis (Grunow) Lange-Bertalot in Lange-Bertalot and Genkal 1999 was reported from reservoirs, but without an image to document the determination (Duong et al. 2006).

The aim of our work was to identify the species diversity of the genus Adlafia in freshwater ecosystems of Vietnam.

Materials and methods

A list of all samples examined in this study with their geographic positions is presented in Table 1. The samples were treated with 10% hydrochloric acid to remove carbonates and washed several times with deionized water for 12 h. The samples were subsequently boiled in concentrated hydrogen peroxide (≈37%) to dissolve organic matter. They were then washed four times with deionized water at 12 h intervals. After decanting and refilling with up to 100 ml deionized water, the suspension was spread onto coverslips and left to dry at room temperature. Permanent diatom preparations were mounted in Naphrax. Light microscopic (LM) observations were performed with a Zeiss Axio Scope A1 microscope equipped with an oil immersion objective (× 100, n.a. 1.4, differential interference contrast [DIC]) and Axiocam ERc 5s camera (Zeiss). Valve ultrastructure was examined by means of a JSM-6510LV scanning electron microscope (IBIW, Institute for Biology of Inland Waters RAS, Borok, Russia). For scanning electron microscopy (SEM), parts of the suspensions were fixed on aluminum stubs after air-drying. The stubs were sputter-coated with 50 nm Au in an Eiko IB 3 sputter coater. Samples and slides are deposited in the public collection of Maxim Kulikovskiy at the Herbarium of the Institute of Plant Physiology Russian Academy of Science, Moscow, Russia. The number of examined valves is indicated in each description of the species. The average value of the valve length, width and striae density, as well as standard deviation were calculated using Microsoft Excel 2020. Terminology of the valve follows Moser et al. 1998; Lange-Bertalot 2001; Morales and Le 2005; Kulikovskiy et al. 2016; Tusset et al. 2017 and Ciugulea et al. 2019.

Table 1.

List of samples examined in this study. Geographic locality of samples and measured parameters indicated.

Sample/Slide Locality Habitat Coordinates Altitude, m Temperature, °C pH Conductivity, µS cm-1 Coll. date
00269 Lâm Đồng Province, Da Tien Reservoir benthos 11°58.816'N, 108°26.987'E 1503 21.5 6.4 81 21.06.2012
00321 Khánh Hòa Province, Hòn Bà Nature Reserve, Dầu River wet moss 12°06.768'N, 108°59.888'E 275 24 6.7 92 28.05.2012
00325 Khánh Hòa Province, Suối Tiên River benthos and periphyton 12°12.199'N, 109°01.694'E 68 26 6.9 101 02.07.2012
02168 Bắc Kạn Province, Ba Bể Lake benthos 22°23.605'N, 105°36.856'E 163 26 8.5 174 19.04.2015
03593 Khánh Hòa Province, Khe River periphyton 12°16.735'N, 108°54.677'E 34 26.8 6.9 84 08.07.2010
04633 Khánh Hòa Province, Hồ Câu Đôi Reservoir periphyton 12°15.750'N, 109°04.012'E 9 29 6.8 110 14.09.2010

Results

Division: Bacillariophyta Haeckel

Class: Bacillariophyceae Haeckel

Naviculaceae incertae sedis

Genus: Adlafia Moser, Lange-Bertalot & Metzeltin in Kulikovskiy et al. (2016)

Adlafia lamdongiensis Glushch., Kulik. & Kociolek, sp. nov.

Figs 1, 2

Holotype

Slide no. 00269 in collection of Maxim Kulikovskiy at the Herbarium of the Institute of Plant Physiology Russian Academy of Science, Moscow, Russia, represented here by Fig. 1A.

Figure 1. 

A–G Adlafia lamdongiensis Glushch., Kulik. & Kociolek sp. nov. LM, DIC, size diminution series. Slides no 00269 (A–C, E–G) and 03593 (D). Holotype (A). Scale bar: 10 μm.

Type locality

Vietnam. Lâm Đồng Province, Da Tien Reservoir, benthos, 11°58.816'N, 108°26.987'E, 1503 m elev., leg. E.S. Gusev, 21.06.2012.

Description

LM (Fig. 1A–G). Valves linear with weakly convex margins. Ends are distinctly narrowly-rostrate. Length 9.7–13 μm (11.4 ± 0.9; n = 16), breadth 2.5–2.8 (2.7 ± 0.1; n = 16) μm. Striae and areolae not resolved in LM.

SEM, external view (Fig. 2A–C). Valve face flat. Axial area linear. Central area absent. Raphe filiform, weakly lateral. Proximal raphe endings slightly expanded. Distal raphe endings positioned on valve mantle, hooked and curved in same direction, terminating at valve face-mantle junction. Striae uniseriate, radiate, becoming abruptly convergent approaching apices, Striae 45–50 in 10 μm (47.5 ± 1; n = 16). Areolae rounded or rectangular, hymenes not preserved during specimen preparation. Slit-like opening of apical areolae arranged in one row onto valve apex. Areolae 40–50 in 10 μm (45 ± 1.8; n = 16).

SEM, internal view (Fig. 2D–F). Raphe slightly lateral, lies in a prominent and raised raphe-sternum. Proximal raphe endings deflected towards primary side of valve. Distal raphe endings terminating in small helictoglossae. Striae continuing onto valve mantle. Short striae alternate with longer striae at valve center. Areolae rounded or rectangular. Openings of apical areolae apically elongated.

Figure 2. 

A–F Adlafia lamdongiensis Glushch., Kulik. & Kociolek sp. nov. SEM. Sample no 00269 A–C external views D–F internal views A whole valve. The valve face is flat B central area C valve end D whole valve E central area F valve end. Scale bars: 2 μm (A), 1 μm (D), 0.5 μm (B, C, E, F).

Etymology

Epithet refers to the province of Vietnam (Lâm Đồng Province) where the specimens were found.

Distribution

Vietnam. Type locality (slide no. 00269) and slide no. 03593.

Adlafia babeiensis Glushch., Kulik. & Kociolek, sp. nov.

Figs 3, 4

Holotype

Slide no. 02168 in collection of Maxim Kulikovskiy at the Herbarium of the Institute of Plant Physiology Russian Academy of Science, Moscow, Russia, represented here by Fig. 3A.

Figure 3. 

A–L Adlafia babeiensis Glushch., Kulik. & Kociolek, sp. nov. LM, DIC, size diminution series. Slide no 02168. Holotype (A). Scale bar: 10 μm.

Type locality

Vietnam. Bắc Kạn Province, Ba Bể Lake, benthos, 22°23.605'N, 105°36.856'E, 163 m elev., leg. E.S. Gusev, 29.04.2015.

Description

LM (Fig. 3A–L). Valves lanceolate with rostrate ends. Length 11.5–14.0 μm (12.8 ± 0.6; n = 21), breadth 4.0–4.5 μm (4.3 ± 0.1; n = 21). Axial area narrow, almost linear. Central area weakly expressed or absent. Raphe filiform. Striae indistinct in LM, weakly radial at the central area, convergent towards to the ends. Areolae not resolved in LM.

SEM, external view (Fig. 4A–C). Valve face flat. Axial area linear. Central area absent. Raphe filiform, weakly lateral. Proximal raphe endings slightly expanded, deflected. Distal raphe endings positioned on the valve mantle, hooked and curved in the same direction, and terminating at the junction valve face-mantle. Striae uniseriate, radiate, becoming abruptly convergent approaching apices, Striae 36–40 in 10 μm (38 ± 0.1; n = 21). Areolae rounded or rectangular, occluded by hymenes. Slit-like opening of apical areolas invisible. Areolae 65–70 in 10 μm (67.5 ± 0.8; n = 21).

SEM, internal view (Fig. 4D). The raphe straight, lying in a prominent and raised raphe-sternum. Proximal raphe endings deflected towards primary side of valve. Distal raphe endings terminating in small helictoglossae. Striae continuing on to valve mantle. Short striae alternate with longer striae at the center of the valve. Areolae rounded. Openings of apical areolae apically elongated.

Figure 4. 

A–D Adlafia babeiensis Glushch., Kulik. & Kociolek, sp. nov. A–C SEM, external views D internal views. Sample no 02168. Scale bars: 2 μm (A, C), 1 μm (B, D).

Etymology

Epithet refers to the lake of Vietnam where the new species was found.

Distribution

Vietnam. Known only from the type locality.

Adlafia vietnamensis Glushch., Kulik. & Kociolek, sp. nov.

Figs 5, 6

Holotype

Slide no. 00325 in collection of Maxim Kulikovskiy at the Herbarium of the Institute of Plant Physiology Russian Academy of Science, Moscow, Russia, represented here by Fig. 5G.

Figure 5. 

A–K Adlafia vietnamensis Glushch., Kulik. & Kociolek, sp. nov. LM, DIC, size diminution series. Slides no 00325 (B–K) and 04633 (A). Holotype (G). Scale bar: 10 μm.

Type locality

Vietnam. Khánh Hòa Province, Suối Tiên River, benthos and periphyton, 12°12.199'N, 109°01.694'E, 68 m elev., leg. E.S. Gusev, 02.07.2012.

Description

LM (Fig. 5A–K). Valves linear-elliptical with capitate to subcapitate ends. Length 15–22 μm (18.5 ± 1.6; n = 20), breadth 3.5–5.0 μm (4.3 ± 0.4; n = 20). Axial area narrow, almost linear. Central area weakly expressed. Raphe filiform. Striae radiate, becoming abruptly convergent approaching apices, 32–34 in 10 μm (33 ± 0.4; n = 20). Areolae not resolved in LM.

SEM, external view (Fig. 6A–C). Valve face flat. Axial area linear. Central area weakly expressed. Raphe filiform. Proximal raphe endings slightly expanded, deflected. Distal raphe endings positioned on the valve mantle, hooked and curved in the same direction, and terminating at the junction valve face. Striae uniseriate. Areolae rounded or rectangular, occluded by hymenes. Slit-like opening of apical areolae invisible. Areolae 50–55 in 10 μm (52.5 ± 1.0; n = 20).

SEM, internal view (Fig. 6D–F). Raphe straight, lying in a prominent and raised raphe-sternum. Proximal raphe endings deflected towards primary side of valve. Distal raphe endings terminating in small helictoglossae. Striae continuing onto valve mantle. Short striae alternate with longer striae at the center of the valve. Areolae rounded or rectangular. The openings of apical areolae apically elongated.

Figure 6. 

A–F Adlafia vietnamensis Glushch., Kulik. & Kociolek, sp. nov. SEM, sample no 00325 A–C external views. D, E internal views A whole valve B central area C valve end D whole valve E central area F valve end. Scale bars: 2.5 μm (A, D), 1 μm (B, C, E), 0.5 μm (F).

Etymology

Epithet refers to the country where the new species was found.

Distribution

Vietnam. Slides no. 00325 (type locality) and no. 04633.

Adlafia dauiensis Glushch., Kulik. & Kociolek, sp. nov.

Figs 7, 8

Holotype

Slide no. 00321 in collection of Maxim Kulikovskiy at the Herbarium of the Institute of Plant Physiology Russian Academy of Science, Moscow, Russia, represented here by Fig. 7C.

Figure 7. 

A–K Adlafia dauiensis Glushch., Kulik. & Kociolek, sp. nov. LM, DIC, size diminution series. Slide no 00321. Holotype (C). Scale bar: 10 μm.

Type locality

Vietnam. Khánh Hòa Province, Hòn Bà Nature Reserve, Dầu River, wet moss, 12°06.768'N, 108°59.888'E, 275 m elev., leg. E.S. Gusev, 2.07.2012.

Description

LM (Fig. 7A–K). Valves linear to linear-elliptical with subcapitate ends. Length 19.0–26.5 μm (22.8 ± 2.3; n = 20), breadth 4.5–5.5 μm (5.0 ± 0.2; n = 20). Axial area narrow, almost linear. Central area weakly expressed. Raphe filiform. Striae radiate, becoming abruptly convergent approaching apices, 32–34 in 10 μm. Areolae not resolved in LM.

SEM, external view (Fig. 8A–C). Valve face flat. Axial area linear. Central area weakly expressed. Raphe filiform. Proximal raphe endings slightly expanded, deflected. Distal raphe endings positioned on the valve mantle, hooked and curved in the same direction, and terminating at the junction valve face-mantle. Striae uniseriate. Areolae rounded or rectangular, occluded by hymenes. Slit-like opening of apical areolae invisible. Areolae 55–60 in 10 μm (57.5 ± 1.1; n = 20).

SEM, internal view (Fig. 8D–F). Raphe straight, lying in a prominent and raised raphe-sternum. Proximal raphe endings deflected towards primary side of valve. Distal raphe endings terminating in small helictoglossae. Striae continuing onto valve mantle. Short striae alternate with longer striae at the center of the valve. Areolae rounded or rectangular. The openings of apical areolae apically elongated.

Figure 8. 

A–F Adlafia dauiensis Glushch., Kulik. & Kociolek, sp. nov. SEM, sample no 00321. A–C external views D, E internal views A whole valve B central area C valve end D whole valve E central area F valve end. Scale bars: 5 μm (A, D), 2.5 μm (B), 1 μm (C, F), 0.5 μm (F).

Etymology

Epithet refers to the river of Vietnam where the new species was found.

Distribution

Vietnam. Known only from the type locality.

Discussion

The four new species described here from Southeast Asia are morphologically similar to each other, but can be differentiated on the basis of valve shape, valve ends and striae density. All species share the morphological features typical for the genus Adlafia. A comparison of species to each other and with previously-described taxa shows that the new species from Southeast Asia are easily distinguished, unique taxa (Table 2).

Adlafia lamdongiensis sp. nov. resembles specimens identified by Lee as Kobayasiella venezuelensis Metzeltin & Lange-Bertalot (2007, p. 155, pl. 141, figs 10–23) specimens as illustrated with light micrographs (Lee 2012, fig. 15, K–M) on the basis of valve outline. Moreover, the valve identified by Lee in the SEM (Lee 2012, fig. 15, N) would appear to belong to the genus Kobayasiella, since there is a characteristic break of the raphe (the “umbilicus”) inherent to representatives of this genus. The valve has noticeably convex edges (Lee 2012, fig. 15, N), while in our material, and the light micrographs of Lee, valves are slightly convex. In our opinion, the light micrographs and a scanning image of Lee (2012) belong to species from different genera.

Table 2.

Morphometric features of new Adlafia species and comparison with similar taxa.

Taxon Outline Valve ends Valve length, μm Valve width, μm Striae in 10 μm Areolae in 10 μm References
A. lamdongiensis sp. nov. linear with weakly convex margins distinctly narrowly-rostrate 9.7–13.0 2.5–2.8 45–50 40–50 This study
A. babeiensis sp. nov. lanceolate rostrate 11.5–14.0 4.0–4.5 36–40 65–70 This study
A. vietnamensis sp. nov. linear-elliptical capitate to subcapitate 15–22 3.5–5.0 32–34 50–55 This study
A. dauiensis sp. nov. linear to linear-elliptical subcapitate 19.0–26.5 4.5–5.5 32–34 55–60 This study
Adlafia multnomahii Morales & Le lanceolate capitate to rostrate 9–16 4–5 37–45 65–70* Morales and Le 2005
A. detenta Heudre, Wetzel & Ector in Ector et al. elliptic to linear-elliptic capitate 15–18 4.5–6.0 28–33 30–35 Heudre et al. 2018
A. neoniana Cantonati in Ciugulea et al. elliptic-lanceolate rostrate to subcapitate 9.4–18.5 3.7–5.1 30–32 45–50 Ciugulea et al. 2019
A. decora Tusset, Tremarin & Ludwig linear-lanceolate rostrate 18.2–26.2 4.6–5.7 24–32 50–54 Tusset et al. 2017
Kobayasiella venezuelensis Metzeltin & Lange-Bertalot sensu Lee Linear with weakly convex margins* subcapitate* 12.7–13.8* 2.7–2.8* no data no data Lee 2012

Adlafia babeiensis sp. nov. resembles Adlafia multnomahii Morales & Le (2005, p. 151, figs 1–38), differing from it mainly by having valves that are more lanceolate in shape and rostrate valve ends (Table 2). In A. multnomahii, on the other hand, the valve ends are capitate to rostrate. The density of striae in both species is similar (35–40 at 10 μm in Adlafia babeiensis sp. nov. in comparison with 37–45 at 10 μm in A. multnomahii). Our species also resembles Adlafia detenta (Hustedt) Heudre, Wetzel & Ector in Heudre et awl. (2018, p. 273), differing from it by the rostrate, rather than bluntly capitate, ends of the valves, striae that are more radiate in their orientation, higher density of striae (36–40 in our species versus 28–33 in 10 μm in A. detenta), and higher density of areolae (65–70 at 10 μm in our species versus 30–33 at 10 μm in A. detenta) (Table 2).

Adlafia vietnamensis sp. nov. resembles Adlafia neoniana Cantonati in Ciugulea et al. (2019, p. 381, figs 1, 2), by having more pronounced capitate ends, as well as less convex valves, in general, with a higher striae density (32–34 at 10 μm for our material compared to 30–32 at 10 μm for Adlafia neoniana) (Table 2). The density of the areolae of our species is also slightly higher (50–55 at 10 μm in Adlafia vietnamensis sp. nov. versus 45–50 at 10 μm in A. neoniana). Adlafia vietnamensis sp. nov. has a linearly elliptical shape of valves and valve ends from rostrate to subcapitate; A. neoniana is characterized by elliptical-lanceolate valves and rostrate to subcapitate ends. Our species is also similar to Adlafia dauiensis sp. nov. (see below) from which it differs mainly by a lower density of striae (50–55 in 10 μm in A. vietnamensis sp. nov. versus 55–60 in 10 μm in A. dauiensis sp. nov.). A. vietnamensis sp. nov. is slightly narrower than A. dauiensis sp. nov. (3.5–5.0 μm versus 4.5–5.5 μm). Valve ends of A. vietnamensis sp. nov. are capitate to subcapitate in shape while in A. dauiensis sp. nov. the ends are subcapitate. The outline of Adlafia vietnamensis sp. nov. is linear-elliptical, while Adlafia dauiensis sp. nov. has a linear to linear-elliptical outline (Table 2).

Adlafia dauiensis sp. nov. resembles Adlafia decora Tusset, Tremarin & Ludwig (2017, p. 261, figs 1–18), differing from it in having capitate, but not rostrate ends, as well as having less convex valves, with a slightly higher striae density (32–34 in 10 μm in our material in comparison with 24–32 to 10 μm in A. decora). The areola density is also different between the two species (50–54 at 10 μm in A. decora versus 55–60 at 10 μm in A. dauiensis sp. nov.) (Table 2).

These new species were found in different water ecosystems of Vietnam that show this genus is widespread in this country, especially in acidic ecosystems.

Morales and Le (2005) suggested Adlafia is a monophyletic group but they did not perform any formal analysis or present data to support their conclusion. Based only on a single species, Thomas et al. (2016) suggested Adlafia is part of a monophyletic group that could be considered the Cymbellales. No other analysis was forthcoming on this taxon, so this work did not address whether Adlafia is a monophyletic genus. Several authors, including in the original description of Adlafia, have made comparisons with Kobayasiella Lange-Bertalot in Lange-Bertalot and Genkal 1999 (as Kobayasia Lange-Bertalot, 1996, non Kobayasia S. Imai & A. Kawamura, 1958; see also Morales and Le 2005; Monnier et al. 2012; Van de Vijver et al. 2017). The two genera have fine striae, external distal raphe ends that are distinctly curved and external hymenate occlusions on the areolae. The difference between the two genera is usually suggested to be the absence (in Adlafia) or presence (in Kobayasiella) of a deflection (umbilicus) in the raphe system. However, this distinction has not always been applied consistently. For example, Le Cohu and Azémar (2010, figs 12, 13) showed specimens of K. jaagi (Meister) Lange-Bertalot, 1999 without the umbilicus. Liu et al. (2017) highlighted areas of the girdle that might help diagnose Adlafia as a monophyletic group, but these observations await formal analysis.

Acknowledgements

Authors are grateful to the staff of the Centre of Electron Microscopy of the Papanin’s Institute for Biology of Inland Waters, RAS, for technical assistance. Samples were collected during expeditions organized and permitted by the Joint Russian-Vietnam Tropical Centre, Ecolan 3.2 theme. Publication is based on research carried out with financial support by Russian Science Foundation (19–14–00320) for LM, SEM, sample investigation and by framework of the state assignment (theme AAAA–A19–119041190086–6) for finishing the manuscript.

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