Review of 'Recent proposals on nomenclature of dinoflagellates (Dinophyceae)'

Some comments to the manuscript titled “Recent proposals on nomenclature of dinoflagellates (Dinophyceae)” by Fernando Gomez

Maria Saburova, Kuwait Institute for Scientific Research, Kuwait

In the present manuscript, the author provides critical comments on some recent nomenclature changes in order to conserve or reject a number of dinoflagellate names, and discusses the resulting nomenclatural stability. I would like to touch on here the nomenclature changes regarding Peridinium acuminatum and Scrippsiella trochoidea.

Recent morphological and molecular revisions of well known dinoflagellate species Scrippsiella trochoidea (F.Stein) A.R.Loeblich III 1976 (Zinssmeister et al., 2011; Kretschmann et al., 2015), on the one hand, have significantly contributed to our knowledge regarding this taxon, but on the other hand, resulted in drastic nomenclature changes affecting a wide range of dinoflagellate taxa (Gottschling and Elbrächter, 2015; (2382), (2383); Prud’homme van Reine, 2017).

Ten years ago, cultural strain of Scrippsiella trochoidea isolated from the type locality, Kiel Fjord, Baltic Sea, Germany, was examined based on morphological and molecular data (Zinssmeister et al., 2011). In their study, the authors isolated cells of Scrippsiella trochoidea from the type locality, established a clonal culture, and investigated the morphology of this strain and its phylogenetic relationships. This comprehensive revision resulted in the designation of epitype for Scrippsiella trochoidea, and in the establishment of an unambiguous link to its protologue, Glenodinium trochoideum F.Stein 1883. The gross morphology of the strain was associated with illustrations of Glenodinium trochoideum by von Stein (Stein, 1883: Pl. III: Figs 27-29), and these line-drawings were designated as a holotype for Scrippsiella trochoidea. Peridinium trochoideum (F.Stein) Lemmerman 1910 was indicated as a synonym (Zinssmeister et al., 2011). In addition, the authors showed that ITS sequence of the strain of Scrippsiella trochoidea from the type locality clustered within the clade comprising strains of this species from the Baltic Sea, Mediterranean Sea, eastern South Atlantic as well as the eastern South and western North Pacific (Zinssmeister et al., 2011).

Just a few years later, the almost same research team came back to the issue of taxonomic and nomenclature clarification of Scrippsiella trochoidea (Kretschmann et al., 2015). The authors again isolated cells of Scrippsiella trochoidea from the type locality (Kiel Fjord), established a clonal culture, and investigated the morphology of this strain. The morphology of this newly established strain was very similar to that of the investigated in the previous study strain in terms of cell color, shape, size, plate pattern, and thecal surface ornamentation. Moreover, both strains exhibited identical ITS sequences (Zinssmeister et al., 2011; Kretschmann et al., 2015). Thus, the later isolated strain of the dinoflagellate resembling Scrippsiella trochoidea was morphologically and phylogenetically indistinguishable from the epitype material of Scrippsiella trochoidea for which the line-drawings of Glenodinium trochoideum (Stein, 1883: Pl. III: Figs 27-29) were designated as a holotype (Zinssmeister et al. in 2011). However, the authors assigned their material to Peridinium acuminatum Ehrenberg, arguing that their taxon is similar to the original illustrations of Ehrenberg for Peridinium acuminatum (Pl. II: Fig. 5 in Ehrenberg, 1835). The replacement of the original material of Scrippsiella trochoidea has taxonomic and nomenclature consequences. Since the original drawing of Ehrenberg for Peridinium acuminatum was assigned as a holotype, and Peridinium acuminatum was recombined with the established taxon Scrippsiella, the name Scrippsiella trochoidea was reassigned as a junior synonym to the proposed new combination, Scrippsiella acuminata (Ehrenb.) Kretschmann, Elbr., Zinssmeister, S.Soehner, Kirsch, Kusber & Gottschling 2015 (Kretschmann et al., 2015).

Given the intricate taxonomic history of Perdinium acuminatum and the fact that the species was designed as type of three gonyaulacoid genera, the recombination of Peridinium acuminatum with Scrippsiella trochoidea has dramatic nomenclature consequences. About 20 species belonging to the peridinioid genus Scripsiella should be transferred to the gonyaulacoid genus Heteraulacus Diesing, since Heteraulacus acuminatus (Ehrenberg) Diesing 1850 has priority over Scrippsiella trochoidea (F.Stein) A.R.Loeblich III 1976. To avoid fatal instability, the authors proposed to conserve Scrippsiella against Heteraulacus and Goniodoma and to reject the family name Goniodomataceae (Kretschmann et al., 2015; Gottschling and Elbrächter, 2015).

Scrippsiella trochoidea is a well recognizable species with a characteristic shape of apex. Its conical epitheca gradually tapers to a short tubular apical process. This morphological character is clearly seen in von Stein's drawings for Glenodinium trochoideum (Stein, 1883: Pl. III: Figs 27-29). I agree with Zinssmeister et al. (2011) in their taxonomic interpretation, undoubtedly recognizing Scrippsiella trochoidea in Stein's drawings. However, following the authors of the new combination (Kretschmann et al., 2015), I am not ready to recognize Scrippsiella trochoidea with the same certainty in Ehrenberg's drawings of Peridinium acuminatum. As the authors noted, “the information Ehrenberg (1833, 1838) provides is not even sufficient to decide whether P. acuminatum is an element of the Peridiniales or of the Gonyaulacales (i.e., diagnostic traits of tabulation wanting)” (Kretschmann et al., 2015).

I believe that the cornerstone of this long and confusing taxonomic and nomenclature history is the original drawings of the Peridinium acuminatum designated as a holotype of this species because of the limited type material available for comparison. Ehrenberg firstly described and illustrated the Peridinium acuminatum in 1835 (Pl. II: Fig. 5 in Ehrenberg, 1835). Both the original description, given as detailed caption to the figures, and the illustrations themselves are rather brief and lack details enough for unambiguous identification when compared to subsequent material. In the earliest drawings of Peridinium acuminatum (Pl. II: Fig. 5 in Ehrenberg, 1835), I see rather peridinioid-like cells with a pointed apex and rounded to flat antapex. The cingulum is indicated, but the sulcus is not drawn. The pointed apex is shown by a hyaline projection sharply protruding from the epitheca. Two years later, Ehrenberg published a formal description of Peridinium acuminatum with a Latin diagnosis and illustrated it with drawings that were probably based on his early design. However, these later illustrations (Pl. XXII: Fig. XVI in Ehrenberg, 1838) differ slightly from the original by more polygonal cell outlines (memory drawing?). This discrepancy between two drawing series assigned by Ehrenberg to the same species opened up a way for subsequent interpretations, resulting in the assignments of this species to different taxonomic groups. Those taxonomists who desired to see Peridinium acuminatum among peridinioid taxa assigned their observations with earlier drawings, while the polygonal shape of cells in later drawings was more fitting for gonyaulacoid taxa.

I agree with the author of the present paper in that the interpretation of the identity of dinoflagellate taxa based on drawings dating back to the first half of the 19th century requires caution. F. Gomez suggests that the somewhat aberrant appearance of the apical protrusion in Ehrenberg's drawings for Peridinium acuminatum could have been due to deformation of the theca, if Ehrenberg observed specimens at the beginning of the ecdysis. I think this is a possible reason, and I can add here one more potential reason for the aberrant appearance of the apex - it could be deformation of cells due to osmotic shock by seawater evaporation during long light microscopic observation under a coverslip. I have occasionally observed hyaline cytoplasmic protrusions of different shape and size from the sulcus or apical pore in dying cells for many dinoflagellate species. This is likely, given Ehrenberg’s notes on Peridinium acuminatum observations that he had too few specimens, and they died while observing and drawing (Ehrenberg, 1835: p. 541: “Scharf isoliren konnte ich sie nicht, weil ich zu wenig Exemplare hatte und diese beim Beobachten und Zeichnen starben, indem ich die ersten, da keine physiologische Beobachtung einen Werth hat, deren Object unsicher ist, wie gewöhnlich der Formbetrachtung opferte.”).

I present here my vision of a complicated taxonomic and nomenclatural issue of only one dinoflagellate species, but one that has so far-reaching implications. Thinking about it, I have dual feeling. On the one hand, I have some experience in dinoflagellate taxonomy. On the other hand, I have been dealing with the microalgal species identification for a long time and I am a regular user of many consequences of nomenclature changes in their taxonomy. Thanks to AlgaeBase (Guiry and Guiry, 2021), in recent years we all have the happy opportunity to clarify quickly and easily the current status of any algal taxon. However, as a reviewer, I often receive manuscripts with the outdated names of microalgae species are still used by a wide range of phytoplanktonists. Nomenclature changes are gradually being adopted by the scientific community.

Stability and simplicity are key requirements of users of scientific names of the species, amongst whom professional taxonomists constitute a relatively small minority. The epitypification of Peridinium acuminatum resulted in name change for well-known, widely used species, Scrippsiella trochoidea. Following nomenclatural change with a new combination, we have to abandon the specific epithet and have to accept an unfamiliar name for this species. These troublesome nomenclatural implications will affect a huge number of phytoplankton researchers, given that a stable species name is the key to its literature, which is especially important for Scrippsiella trochoidea as a widespread species that has been the subject to many ecological, taxonomic and palaeo-environmental publications.

References

Ehrenberg, C.G. (1835). Das Leuchten des Meeres: neue Beobachtungen nebst Übersicht der Hauptmomente der geschichtlichen Entwicklung dieses merkwürdigen Phänomens. Abhandlungen der Königlichen Akademie der Wissenschaften zu Berlin 1834: 411-575 (Ein in der Königl. Akademie der Wissenschaften im April 1834 gehaltener Vortrag, mit einigen Zusätzen gedruckt im October 1835).

Ehrenberg, C.G. (1838). Die Infusionsthierchen als volkommene Organismen. Ein Blick in das Tiefere organische Leben der Natur. Leipzig, Leopold Voss, 547 pp.

Gottschling, M., Elbrächter, M. (2015). (2382) Proposal to conserve the name Scrippsiella against Heteraulacus and Goniodoma (Thoracosphaeraceae, Dinophyceae). Taxon 5: 1051–1052.

Guiry, M.D., Guiry, G.M. (2021). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 26 April 2021.

Kretschmann, J., Elbrächter, M., Zinssmeister, C., Soehner, S., Kirsch, M., Kusber, W.-H., Gottschling, M. (2015). Taxonomic clarification of the dinophyte Peridinium acuminatum Ehrenb., ≡ Scrippsiella acuminata, comb. nov. (Thoracosphaeraceae, Peridiniales). Phytotaxa 220(3): 239-256.

Prud’homme van Reine, W.F. (2017). Report of the Nomenclature Committee for Algae: 17. Taxon 66(2): 481-482.

Stein, F.R. von (1883). Der Organismus der Infusionsthiere nach eigenen Forschungen in systematischer Reihenfolge bearbeitet. II. Hälfte. Einleitung und Erklärung der Abbildungen. Wilhelm Engelmann, Leipzig, 30 pp.

Zinssmeister, C., Soehner, S., Facher, E., Kirsch, M., Meier, K.J.S., Gottschling, M. (2011). Catch me if you can: The taxonomic identity of Scrippsiella trochoidea (F.Stein) A.R.Loebl. (Thoracosphaeraceae, Dinophyceae). Systematics and Biodiversity 9:145-157.