Wallidinellum, Bauer & Gottschling & Keupp & Kusber & Mertens, 2021

Bauer, Wolfgang, Gottschling, Marc, Keupp, Helmut, Kusber, Wolf-Henning & Mertens, Kenneth N., 2021, Validation of the calcareous dinophyte Wallidinellum (Peridiniales), with notes on the status of fossils in the Code, Phytotaxa 520 (3), pp. 296-300 : 296-298

1. Wallidinellum dalei Keupp ex Gottschling, W.Bauer, K.N.Mert. & Keupp , gen. & sp. nov.

Descriptio generico-specifica (ICN Art. 38.5): Coccoid cell microgranular, calcitic, with ortho-hexa-tabulation incompletely expressed by external, obtuse ridges. This expression is particularly prominent in the precingular and antapical equivalents.

Holotype [non-fossil]: Indian Ocean, western Arabian Sea. Date and precise locality of the single gathering was not specified: D. Wall & B. Dale C216 (deposited at SPWH). The species is described and illustrated in Wall & Dale (1968a: pl. IV 23) and Wall & Dale (1968b: figs 4–9, pl. CLXXII 5–6). This taxonomic act has been registered in PhycoBank under http://phycobank.org/102891.

2. excluded designations

“ Pentadinellum ” Keupp (not validly published, ICN Art. 44.1: In order to be validly published, a name of a new taxon of non-fossil algae published between 1 January 1958 and 31 December 2011, inclusive, must be accompanied by a Latin description or diagnosis) in Riding, Calcareous Algae and Stromatolites: [267, 270,]283[, 284]. 1991. Type species: Pentadinellum oblatum Keupp , not validly published.

†“ Pentadinellum cretaceum” Keupp (nom. corr. ICN Art. 32.2, not validly published: ICN Art. 35.1: A name of a taxon below the rank of genus is not validly published unless the name of the genus or species to which it is assigned is validly published at the same time or was validly published previously), Berliner Geowissenschaftliche Abhandlungen. Reihe E 3: 131–132, pl. V 6–10. 1992 .

“ Pentadinellum oblatum” Keupp (not validly published, ICN Art. 35.1: A name of a taxon below the rank of genus is not validly published unless the name of the genus or species to which it is assigned is validly published at the same time or was validly published previously) in Riding, Calcareous Algae and Stromatolites: 283. 1991.

†“ Pentadinellum vimineum” Keupp (not validly published, ICN Arts 35.1: A name of a taxon below the rank of genus is not validly published unless the name of the genus or species to which it is assigned is validly published at the same time or was validly published previously; 41.5: On or after 1 January 1953, a new combination, ... is not validly published unless its basionym ... is clearly indicated and a full and direct reference given to its author and place of valid publication, with page or plate reference and date), Berliner Geowissenschaftliche Abhandlungen. Reihe E 3: 132–133, pl. VI 1–2. 1992 .

“ Wallidinellum ” Keupp (not validly published, ICN Art. 44.1: In order to be validly published, a name of a new taxon of non-fossil algae published between 1 January 1958 and 31 December 2011, inclusive, must be accompanied by a Latin description or diagnosis) in Riding, Calcareous Algae and Stromatolites: [267, 268, 271,]282–283. 1991. Type species: Wallidinellum dalei Keupp , not validly published .

“ Wallidinellum dalei” Keupp (not validly published, ICN Art. 35.1: A name of a taxon below the rank of genus is not validly published unless the name of the genus or species to which it is assigned is validly published at the same time or was validly published previously) in Riding, Calcareous Algae and Stromatolites: 283. 1991.

The taxa under consideration here have rarely been encountered since their first description by Keupp (1991). Of “ Pentadinellum oblatum ”, motile cells were incubated initially from coccoid cells collected in surface sediments off Bermuda in the North Atlantic Ocean ( Wall & Dale 1968a: pl. IV 26, 1968 b: pl. CLXXII 21–22). Later, these cells were tentatively associated with Ensiculifera mexicana Balech ( Wall et al., 1970: 155; Keupp, 1991: 283), the type of Ensiculifera Balech. This interpretation was recently confirmed ( Li et al., 2020), which makes the validation of the initial name superfluous (ICN Art. 36.1: A name is not validly published when it is not accepted by its author in the original publication ...). However, the characteristically oblate cells were also associated with Cretaceous fossils, and we discussed the option to validate “ Pentadinellum ” based on fossils. This proceeding would slightly alter the original identity (a non-fossil name is changed to a fossil name because the type would represent a fossil-taxon), but would link the fossils with the extant coccoid cells of E. mexicana . This was the explicit aim of Keupp (1991, 1992) and adopted by, for example, Wendler & Willems (2002) and Wendler et al. (2002). However, all physical material of the fossils is destroyed (in the sense of Gravendyck et al., in press) and for fossil-taxa, the type is always a specimen (ICN Art. 8.5). This makes a validation of “ Pentadinellum ” based on original material from Calais or Hildesheim (i.e., the type localities) impossible at this moment in time, since these localities would need to be re-sampled.

Wall & Dale (1968b) were also able to establish motile cells of W. dalei , gen. & sp. nov., and they assigned these to Scrippsiella sweeneyae Balech , the type of Scrippsiella Balech. In contrast to the cells assigned to Ensiculifera , the taxonomy of Wallidinellum , gen. nov., is rather elusive for several reasons, including the diffuse circumscription of Scrippsiella and its delimitation from taxa such as † Calciodinellum Deflandre and Duboscquodinium Grassé ( Gottschling & Söhner, 2013). Strain CCCM280 of unknown origin has been identified as S. sweeneyae , but has not produced coccoid cells for observation ( Gottschling et al., 2005b; Kretschmann et al., 2014). Species with known coccoid cells, such as Scrippsiella bicarinata Zinssmeister, S.Soehner, S.Meier & Gottschling ( Zinssmeister et al., 2012), may resemble W. dalei , gen. & sp. nov., morphologically. In conclusion, many taxonomic identities are ambiguous in Scrippsiella and related taxa that the initial and its somewhat naïve association of W. dalei , gen. & sp. nov. ( Wall & Dale 1968b), must be seen with considerable reservation.

The nature of the archaeopyle and the associated operculum has importance for the assignment of species to groups at higher taxonomic levels among calcareous dinophytes ( Streng et al., 2004; Gottschling et al., 2005a). Ensiculifera has an apical archaeopyle interpreted as involving the plate 3ˊ equivalent as present in, for example, Ensiculifera tyrrhenica (Balech) Zhun Li, K.N.Mert., Gottschling, H.Gu & H.H. Shin (=† Calcicarpinum bivalvum G.Versteegh ; Li et al., 2020). The interpretation of the archaeopyle is more difficult for W. dalei , gen. & sp. nov. The species is not listed in the extensive compilation of Streng et al. (2004), but a compound mesoepicystal operculum disintegrating into pieces was noted by Streng (2003). Such an operculum is otherwise not known from extant calcareous dinophytes. The images provided by Wall & Dale (1968a, b), however, seemingly show a simple mesoepicystal operculum with plate equivalents not separated. This operculum type is very common in the lineage of Scrippsiella and considered an apomorphy of the corresponding group (Gottschling, et al., 2005a). Such an archaeopyle in W. dalei , gen. & sp. nov., would support its assignment to the Scrippsiella lineage, as previously suggested by Wall & Dale (1968b).

Beyond the morphological information, DNA sequence data are now available for E. mexicana ( Li et al., 2020) but not for W. dalei , gen. & sp. nov. An epitypification approach, successful in the past for other protists ( Zinssmeister et al., 2011; Kretschmann et al., 2018; Žerdoner Čalasan et al., 2020; Tillmann et al., 2021), may clarify the taxonomic circumscription and status in future. Such work will also uncover more comprehensive morphological data going beyond the limited information provided by Wall & Dale (1968a, b), which nevertheless is all we currently know about the organism. It is particularly important to decide whether the taxa are to be synonymised under older names or are to be retained separately. However, this is impossible as long as the coccoid cells of S. sweeneyae are unknown and as long as there is no consistent concept for the classification of Scrippsiella in a broad sense. Until the relation of the here validated taxa is not resolved, all authors of the present Correspondence accept them as distinct taxonomic entities.

Dinophyte development is complex and frequently includes at least two morphologically differentiated stages of lifehistory, namely a flagellated cell and a coccoid cell ( Stosch, 1973; Pfiester & Anderson, 1987). The nomenclatural type of W. dalei , gen. & sp. nov., is a coccoid cell (or frequently termed ‘cysts’ in the literature). A great morphological and functional diversity of such cells is well established ( Fensome et al., 1993; Mertens et al., 2012), and they are usually deposited in sediments during life-history, where they germinate a new generation (or may fossilise). As a result, the vast majority of fossil dinophyte taxa are typified based on specimens of coccoid cells, whereas many non-fossil dinophyte taxa are typified based on (images or) specimens of flagellated cells (Gravendyck et al., in press).

The International Code of Nomenclature for algae, fungi, and plants (the Code; Turland et al., 2018) distinguishes between the two categories ‘non-fossil’ and ‘fossil’ and has developed rules and provisions regarding starting-points (Art. 13) or priority (Art. 11). Accordingly to Art. 13.3, ‘fossil material is distinguished from non-fossil material by stratigraphic relations at the site of original occurrence’ (see also discussion in Turland, 2019). Sediments have ‘stratigraphic relations’ and subsequently, the ‘fossil’ status tends to be assumed for all names typified based on dinophyte coccoid cells ( Williams et al., 2017). However, Wallidinellum , gen. nov., demonstrates that coccoid cells can in fact be assigned to the ‘non-fossil’ status as well, comparably to most of the flagellated cells. A similar case has been made for Brigantedinium simplex (D.Wall) P.C.Reid ex Lentin & G.L.Williams ( Lentin & Williams, 1981: 29; Fensome et al., 1991: 105; Lentin & Williams, 1993: 67; Williams et al., 2017: 128‒129), which is typified based on an illustrated coccoid cell collected from an aquarium at the Woods Hole Oceanographic Institution ( Wall, 1965). Another example is Peridinium anglicum G.S.West representing the coccoid stage of Palatinus apiculatus (Ehrenb.) Craveiro, Calado, Daugbjerg & Moestrup ( Craveiro et al., 2009).

For unicellular and other organisms, it is important to conclude that there is no necessary link between the ‘fossil’ status in the sense of the Code and to remnants such as shells, coats and scales (chrysophytes, coccolithophorites, diatoms) or to a specific stage of life-history such as complete coccoid cells (chlorophytes, chrysophytes, dinophytes). Fossilisation takes places during a taphonomic process, which is not necessarily a discrete event and subsequently, the boundary between ‘nonfossil’ and ‘fossil’ is diffuse. Beyond the criterion of having ‘stratigraphic relations’, a more precise definition of a ‘fossil’ for nomenclatural purposes is desirable to reduce ambiguity. All confusion that arises around the distinction between ‘nonfossils’ and ‘fossils’ was eliminated if both categories would be treated equally, as it takes place in the International Code of Zoological Nomenclature ( Ride et al., 1999) and for diatoms in the Code ( Turland, 2019), which may be considered in the future.