Abstract
The order Gymnodiniales comprises unarmoured dinoflagellates. However, the lack of sequences hindered determining the phylogenetic positions and systematic relationships of several gymnodinioid taxa. In this study, a monophyletic clade was defined for the species Ceratoperidinium margalefii Loeblich III, Gyrodinium falcatum Kofoid & Swezy, three Cochlodinium species, and two Gymnodinium-like dinoflagellates. Despite their substantial morphotypic differentiation, Cochlodinium cf. helix, G. falcatum and 'Gymnodinium' sp. 1 share a common shape of the acrobase. The phylogenetic data led to the following conclusions: (1) C. margalefii is closely related to several unarmoured dinoflagellates. Its sulcus shape has been observed for the first time. (2) G. falcatum was erroneously assigned to the genus Gyrodinium and is transferred to Ceratoperidinium (C. falcatum (Kofoid & Swezy) Reñé & de Salas comb. nov.). (3) The genus Cochlodinium is polyphyletic and thus artificial; our data support its separation into three different genera. (4) The two Gymnodinium-like species could not be morphologically or phylogenetically related to any other gymnodinioid species sequenced to date. While not all studied species have been definitively transferred to the correct genus, our study is a step forward in the classification of inconspicuous unarmoured dinoflagellates. The family Ceratoperidiniaeceae and the genus Ceratoperidinium are emended.
Highlights
Approximately 5·105 species of protists are currently known and described (Adl et al 2007), extensive molecular analyses indicate an estimated diversity several orders of magnitude higher (Adl et al 2007; López-García et al 2001; Savin et al.2004), including numerous cryptic species (Amato et al 2007; Katz et al 2005; Montresor et al 2003; Quijano-Scheggia et al 2009)
Ceratoperidinium Margalef ex Loeblich III already exists for a species that is unambiguously located within this clade, C. margalefii, we suggest that Gyrodinium falcatum properly belongs in the genus Ceratoperidinium
The partial LSU rDNA sequences obtained in this study are evolutionarily very close and form a highly supported new clade, despite substantial differences in the morphologies of the respective unarmoured dinoflagellates
Summary
Approximately 5·105 species of protists are currently known and described (Adl et al 2007), extensive molecular analyses indicate an estimated diversity several orders of magnitude higher (Adl et al 2007; López-García et al 2001; Savin et al.2004), including numerous cryptic species (Amato et al 2007; Katz et al 2005; Montresor et al 2003; Quijano-Scheggia et al 2009). Dinoflagellate diversity has been estimated at approximately 2,000 species These organisms were classified based on morphological features, including the presence and arrangement of their thecal plates (Saldarriaga et al 2004). The taxonomic position of the genus Ceratoperidinium has long been uncertain (Fensome et al 1993; Sournia 1986) and its two species, C. margalefii and C. mediterraneum Abboud-Abi. Saab, have been considered as morphological variants of a single one (Gómez et al.2004). Given the unreliability of gross external morphology in determining the true phylogenetic and taxonomic affinities of unarmoured dinoflagellates, we carried out a detailed investigation of the morphology and LSU rDNA phylogeny of C. margalefii, G. falcatum, three ‘Cochlodinium’ morphospecies and two ‘Gymnodinium’.
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