(C) 2014 Marie-Josèphe Chrétiennot-Dinet. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Citation: Chrétiennot-Dinet M-J, Desreumaux N, Vignes-Lebbe R (2014) An interactive key to the Chrysochromulina species (Haptophyta) described in the literature. PhytoKeys 34: 47–60. doi: 10.3897/phytokeys.34.6242
We present a general overview of features and technical specifications of an original interactive key web application for the identification of Chrysochromulina species. The list of species, originally described as belonging in the genus Chrysochromulina, is given and recent taxonomic changes in species and genera of the order Prymnesiales are provided. We briefly discuss the interest of such a key for the identification of phytoplanktonic species.
Interactive key, identification tool, XPER², web application, morphology, description protocol, phytoplankton, Chrysochromulina
The genus Chrysochromulina, erected by
The class name Haptophyceae was first used by Christensen in 1962 but Hibberd introduced the typified class name Prymnesiophyceae (Hibberd 1976), both names being considered as valid. More recently
Within the class, the genus Chrysochromulina was for a long time placed in the order Prymnesiales and the family Prymnesiaceae. However, from DNA phylogenies and morphological comparisons,
As we are dealing here with an identification key, we have taken into consideration all species originally described as Chrysochromulina in the literature (or moved to this genus as for Chrysocampanula spinifera (Fournier) by
The key covers 58 species originally described as Chrysochromulina. References for publications dealing with their description and occurrence are given. A detailed description is provided and illustrations of a whole cell as well as for the different scale types, in some cases from unpublished material seen in SEM, are included. It is noticeable that two of them have different morphologies described as “forma”: Chrysochromulina polylepis , now Prymnesium polylepis, “authentic” or “alternate” (
Chrysochromulina acantha Leadbeater & Manton (1971); Chrysochromulina adriatica
The key matrix is based on one ecological character (habitat) and 19 morphological descriptors seen in light or electron microscopy, under live conditions or after fixation for EM observations. They range from cell shape to scale ornamentation. Details of scales can be obtained by specific techniques with TEM, such as direct preparations (
HABITAT: marine, brackish, freshwater
SHAPE: spherical-subspherical, elongate to round, lanceolate, saddle-shaped
CELL LENGTH, CELL WIDTH: min. and max. sizes are given for each form or species.
FLAGELLA: Two flagella are present and may be equal or sub-equal, in that case the length of the longer and shorter flagellum are given.
HAPTONEMA BEHAVIOR: coiling, rarely coiling, non coiling.
HAPTONEMA LENGTH: min. and max. size (in some cases, the haptonema may be very long)
NUMBER OF SCALE TYPES: in some cases, scales may be displayed in several layers and show up to four different types but there is always a layer of plate scales as cell covering.
SCALE APPENDICES: besides plate scales, a number of different appendices can be observed : spine, cylinder or another typical ornamentation.
PLATE SCALE LENGTH AND WIDTH: min. and max. sizes are given for all plate scales.
The interactive key is developed using Xper2 version 2.2 software. It is free software available with multilingual interface and compatible with different OS (Windows, MacOS and Linux) under a creative commons license (BY-CC-ND). You can download it on http://www.infosyslab.fr and find on this website a complete documentation with technical details, user manual and knowledge bases.
Xper2 offers an editor to structure and analyse descriptive data and an interface for interactive free access key (
We installed the interactive key on a web server with Apache2, choosing the English interface. This content is under a creative commons license (BY-CC-ND), except when a special information is attached to images.
Xper2 manages structured descriptive data: all the terminal taxa of the key are described using the same terms (descriptor and character states labels), and so the taxa can be compared automatically.
Figure 1 presents the comparison of the two forms attributed to Prymnesium palpebrale (previously Chrysochromulina palpebralis). The different colors allow to point easily where the descriptions are distinct, overlap, or are the same. Here the two forms differ on scale type number and appendices.
Comparison of the two forms of Prymnesium palpebrale. The two forms are very similar and differ only on scales and appendices.
In the same way the comparison of the five species (Haptolina brevifila, Haptolina ericina, Haptolina fragaria, Haptolina herdlensis and Haptolina hirta) previously known as Chrysochromulina but attributed in 2011 in the new genus Haptolina (
Comparison of the five species of the new genus Haptolina. The column «intersection» on the right side gives the values shared by the five species.
Our key of the Chrysochromulina species is a free access key accessible at http://www.obs-banyuls.fr/chrysochromulina . It offers an interactive and flexible way to identify these phytoplanktonic species.
A classical polytomous key consists of a series of questions (characters), each one offering alternative statements (
Figure 3 shows the screen during an identification process. Each item (terminal taxon of the key) is documented by a text including nomenclatural data, type locality, literature references and morphological data, and is illustrated by several images. Descriptors and character states are also documented and illustrated.
Example of screen of the free access key. On the left the user chooses descriptor and states with the help of the additional ressources, text and images in the center of the screen. On the right the lists of remaining and eliminated species.
Example of descriptors (in red) that allow differentiation between Chrysochromulina lanceolata and a specimen under identification.
At each step, the user may ask the software to find the best characters to distinguish the possible taxa. Three different measures are proposed Xper, Jaccard, and Sokal & Michener (as ”Best descriptors” in the select box). For each pair of remaining taxa, each coefficient measurement compares the possible states and the final result is the sum for all the pairs. Xper coefficient checks only if there is no overlap (it means the two taxa may be completely distinct on this character) and so the measure for one pair of taxa is 0 (if overlapping) and 1 (if no overlapping). Jaccard coefficient was initially developed to compare sets of binary characters; here the states are considered as the binary characters and the comparison takes into account the ratio between the number of states possible for only one taxon of the pair and the number of states possible for at least one taxon of the pair. In the Sokal & Michener coefficient, the states which are not possible for the two taxa are also taken into account. The three measures are described in Burguière et al. (2013).
Identification of Chrysochromulina species has long been reserved to specialists as it is a major difficulty for most phytoplanktonologists. The cells are very small, often overlooked or placed as “unidentified” species in field studies. Cultures and specific preparations are generally needed to get relevant information on morphological features. A key for identification of Scandinavian species (
We thank Valérie Domien for creating the home page and for drawing illustrations of Chrysochromulina brachycylindra and Jennifer Guarini for corresponding with editors about copyright.
We also thank the reviewers for their very constructive comments.