Nematodinium parvum (Lohmann) Moestrup, 2023

García-Portela, María, Moestrup, Øjvind, Daugbjerg, Niels, Altenburger, Andreas & Lundholm, Nina, 2023, Studies on the complex Warnowiaceae (Dinophyceae) I. Lohmann’s Pouchetia parva refound and renamed Nematodinium parvum comb. nov. (= Warnowia parva), Phycologia 62 (5), pp. 421-435 : 433-434

Nematodinium parvum (Lohmann) Moestrup comb. nov.

BASIONYM: Pouchetia parva Lohmann 1908 , Wissenschaftliche Meeresuntersuchungen, Abteilung Kiel 10, p. 264, pl. XVII, fig. 23.

HOMOTYPIC SYNONYM: Warnowia parva (Lohmann) Er. Lindemann (1928, p. 52) .

HETEROTYPIC SYNONYM: Nematodinium pseudoarmatum Hovasse (1951, p. 151) .

Whether the two genera, Nematodinium and Warnowia , are separate genera must await examination of the type species of Nematodinium , N. partitum , originally described from La Jolla, California, and the type species of Warnowia , W. fusus (F. Schütt) Er. Lindemann , of uncertain origin but probably from the Bay of Naples or the Atlantic. It will cause some confusion if they have to be merged, as the name Nematodinium is older than Warnowia and the family name is Warnowiaceae .

Are Nematodinium armatum and Nematodinium parvum different species?

The two species are very similar, but an important difference appears to be the length of the cell and the typically conical shape of the antapex in N. parvum . Dogiel (1906) gave the cell length of N. armatum as c. 50 µm, while Lohmann (1908), as mentioned above, described N. parvum to be 33 µm long. Neither author gave information on cell width. Hulburt (1957) provided a size range of his material from Massachusetts, in N. armatum 33–53 µm long and 20–33 µm wide, and in Warnowia parva 22.5–30 µm long and 15–18 µm wide. If these differences hold, the two species are different, although Lebour (1925) stated the size of N. armatum as 28–50 µm and suggested that the cells described by Lohmann may have been encysted N. armatum . Considering that our material was very constant in size and never exceeded 39 µm, we currently regard N. armatum and N. parvum as different species.

In the phylogenetic tree based on LSU rDNA ( Fig. 43 ), the sister taxon to N. parvum was a sequence ( FJ947041 ) of Nematodinium sp. from Hoppenrath et al. (2009), which is illustrated in their figs 1M– 1P. The images show a yellowish cell with a cell length and shape more or less similar to N. armatum . This appears to support the conclusion above and to show the close relationship between N. parvum and N. armatum .

Phylogenetic inferences

The phylogenetic analyses conducted here, based on SSU and LSU rDNA, highlight the same challenge: very few warnowiaceans have been identified to the level of species. This makes the available molecular sequences of little use for phylogenetic inferences clarifying the taxonomy of the ocelloid-bearing dinoflagellates. Additionally, the phylogenetic trees also confirm the present state of confusion at the generic level: both Nematodinium and Warnowia taxa clustered within multiple lineages, as shown in Fig. 42 and to some extent in Fig. 43 . Since so few single-cell isolates have been determined for both ribosomal genes and morphologically characterized at the same time, concatenation would not have improved the outcome.

The numerous uncultured eukaryotes from Sargasso and polar seas clustering with the warnowiaceans ( Fig. 42 ) reveal the widespread biogeography of the Warnowiaceae . However, understanding their distribution pattern and ecological importance will require precise taxonomic identification.

Figures

Fig. 43. Phylogeny of 10 ocelloid-bearing dinoflagellates identified to genus level (one to species level) analysed using Bayesian analysis and inferred from partial LSU rDNA sequences. Lepidodinium and Gymnodinium formed the outgroup taxa. Numbers at internodes represent posterior probabilities from Bayesian analysis and bootstrap values from RAxML (10,000 replicates). Filled circles indicate maximal support (1.0 in posterior probability and 100% in RAxML). Branch lengths are proportional to the number of character changes, see scale bar. Newly sequenced cell isolates are written in bold.

Fig. 42. Phylogeny of 13 ocelloid-bearing dinoflagellates identified to genus level (one to species level) and seven uncultured eukaryotes anticipated to possess ocelloids analysed using Bayesian analysis and inferred from SSU rDNA sequences. Lepidodinium and Gymnodinium formed the outgroup taxa. Numbers at internodes represent posterior probabilities from Bayesian analysis and bootstrap values from RAxML (10,000 replicates). Filled circles indicate maximal support (1.0 in posterior probability and 100% in RAxML). Branch lengths are proportional to the number of character changes, see scale bar. Newly sequenced cell isolate is written in bold.