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    Review of 'Excessive proliferation of new dinoflagellate generic names: the case of Torquentidium (Ceratoperidiniaceae, Dinophyceae)'

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    Excessive proliferation of new dinoflagellate generic names: the case of Torquentidium (Ceratoperidiniaceae, Dinophyceae)

     Fernando Gomez (corresponding) (2019)
    New genera of unarmoured dinoflagellates represented by a single or very few species have largely increased in the last two decades. An example is the new genus name Torquentidium H.H. Shin, Z. Li, K.W. Lee & Matsuoka 2019 (Shin et al. , Eur. J. Phycol . 54: 249-262) recently proposed for species that were transferred into Pseliodinium in 2018. The SSU- and LSU rRNA gene sequences of the type species of Pseliodinium and Torquentidium only differed by 0.3% and 2%, respectively, and they clustered together as a monophyletic group with high support. Based on these tree topologies and/or the sequence divergences, each dinoflagellate species would be classified in its own genus. The morphological character proposed to distinguish Pseliodinium and Torquentidium is that the cingulum encircled the cell 1 and 1.5 times, respectively. This kind of arbitrary numeric morphometric character, proposed one century ago, is currently considered invalid for the generic split of unarmoured dinoflagellates. For example, Polykrikos geminatum (with ~1.5 cingular turns) clusters between species of Polykrikos (1 turn). Within the Ceratoperidiniaceae, the arrangement of the amphiesmal vesicles in apical structure complex was used for distinction at the genus level (i.e., Kirithra ), while this character is identical for Pseliodinium and Torquentidium . For the first time, an unarmoured dinoflagellate genus contains species with smooth cell covering ( T. convolutum , T. helix ) and species with longitudinal striae ( T. pirum ). However, the original description as Gymnodinium pirum in 1895 erroneously illustrated two distinct species, and since then nobody has ever reported surface markings in T. pirum . The morphological and molecular criteria used for the split of Torquentidium from Pseliodinium are unsupported, contributing to the excessive proliferation of monotypic genera. Torquentidium pirum and T. convolutum are synonyms, and Torquentidium is a superfluous generic name and junior synonym of Pseliodinium .
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      Review information

      10.14293/S2199-1006.1.SOR-LIFE.APWN5AK.v1.RIZVRS

      This work has been published open access under Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Conditions, terms of use and publishing policy can be found at www.scienceopen.com.

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      Review text

      Name changes always cause concern and confusion among non-specialists, but reflect the ever developing understanding of natural relationships among organisms.  Still, original names should be retained as much as possible until complete information is available on the existing available and valid genera and species. The additional tool of the International Code of Nomenclature for Algae, Fungi, and Plants (Shenzhen Code 2017) aims to produce nomenclatural stability, rather than generate excessive proliferation of new names (as the title of this paper warns against).

       

      Dinoflagellate taxonomy is currently in a state of flux; initially based exclusively on morphology, now increasingly molecular genetics is used as an additional tool. Sometimes morphology and genetics match, but not always. The more genes (LSU, SSU, ITS, chloroplast and mitochondrial genes) we use, and the more species we sequence, the best chance we have to come up with a classification that reflects phylogeny.

       

      Following an initial focus by dinoflagellate taxonomists on classical unarmoured genera such as Gymnodinium, Gyrodinium, Karenia, Karlodinium, Akashiwo, current attention addresses unarmoured gymnodinioid dinoflagellates with twisted, helical girdle grooves, initially all covered under the name Cochlodinium.

       

      Some Cochlodinium species (polykrikoides, fulvescens) were recently transferred by Gomez et al. (2017) to the new genus Margalefidinium. Perhaps a case could have been made to conserve the name Cochlodinium for this commercially important fish-killing taxon, but alas that was not done.  Gomez (2018) also already proposed to revive the existing genus name Pseliodinium Sournia 1972 for C. helix and C. pirum (the latter considered conspecific with the later described C. convolutum).

       

      Shin et al. (2019) recently created a new genus Torquentidium for C. convolutum (which they comprehensively studied themselves) as well as including in this new genus  C. helix. and C.pirum (but which they did not study, and which therefore causes some uncertainty of interpretation). C. pirum (as Pseliodinium pirum) has now more recently been independently studied by Hu et al. (2019; early view paper in Phycological Research), which from their illustrations clearly is a junior synonym of C. convolutum. As such indeed the creation of the genus Torquentidium seems superfluous.

       

      Now Shin et al. (2019) is close to being formally been published, the LSU sequence MF948386 of Korean Torquentidium convolutum should be available, and can be compared to the Chinese sequence of Pseliodinium pirum MH469535. It serves no purpose to guess “it probably is identical” (p. 5). Just wait for the sequence, or ask the authors directly. As previously explained by Gomez (2018) the original interpretation of Cochlodinium pirum by Schütt 1895 differs from the later interpretation by Kofoid & Swezy 1921 (with striated pellicle), and we now have available identical molecular sequences for organisms labelled as C. cf. helix, P. pirum and T. convolutum. This calls for a resolution.

       

      I broadly agree with the statements of content of this note by Gomez,  but strongly believe this message will be lost here, and best should be published in a Phycological Journal (e.g. Phycologial Research?) or otherwise the journal Taxon.  Regrettably European J Phycology does not take comments papers, but it is unprofessional to blame (and name) this on the Editor.

       

       

      A number rambling exaggerated statements should be deleted:

       

      p.9, line 10 “ If Shin’s practice extends to other dinoflagellate species, the concept of genus will disappear….”

       

      p.14, line 17 from below. “etymology of dium” “so much twist should not disorient us.””. The wordplay on Torquentidinium [sic] is distracting!

       

      The structure of this paper can be improved, starting with morphology, based on light and electron microscopy, then moving to molecular data, before going into the detail of the strains studied by Shin et al. 2019, Hu et al. 2019, Rene et al. 2013, ending with the taxonomic resolution. Not going back to Schütt 1895 Kofoid & Swezy 1921 again in the final pages, thereby creating a circular argument.

       

      Why not shortening this manuscript considerably as: “The cochlodinioid dinoflagellate Torquentidium convolutum (Kofoid & Swezy) Shin, Li, Lee & Matsuoka is a junior synonym of Pseliodinium pirum (Schütt) Gomez

       

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