Balechina and the new genus Cucumeridinium gen. nov. (Dinophyceae), unarmored dinoflagellates with thick cell coverings

Abstract

The genus Balechina (=subgenus Pachydinium) was established for heterotrophic gymnodinioid dinoflagellates with a thick cell covering. The type species, B. pachydermata (=Gymnodinium pachyderm-atum), showed numerous fine longitudinal striae, whereas B. coerulea (=G. coeruleum) showed ~24 prominent longitudinal surface ridges or furrows and a distinctive blue pigmentation. We have investigated the morphology and molecular phylogeny of these taxa and the species Gymnodinium cucumis, G. lira and G. amphora from the western Mediterranean, Brazil and Japan. Sudden contractions at the cingulum level were seen in B. pachydermata, which also showed a high morphological variability which included morphotypes that have been described as Amphidinium vasculum, G. amphora, G. dogielii and G. gracile sensu Kofoid and Swezy. Molecular phylogeny based on small subunit rRNA gene sequences revealed that Balechina coerulea, G. cucumis and G. lira formed a clade distantly related to the clade of the type species, B. pachydermata, and G. amphora. We propose the new genus Cucumeridinium for the species with longitudinal ridges and a circular apical groove (Cucumeridinium coeruleum comb. nov., C. lira comb. nov. and C. cucumis comb. nov.), and Gymnodinium canus and G. costatum are considered synonyms of C. coeruleum. The genus Balechina remains for the species with a double-layer cell covering, bossed surface with fine striae, and an elongated elliptical apical groove. At present, the genus is monotypic containing only B. pachydermata.

Molecular characterization and morphology of Cochlodinium strangulatum , the type species of Cochlodinium , and Margalefidinium gen. nov. for C. polykrikoides and allied species (Gymnodiniales, Dinophyceae)

“…Similar examples can be found in the morphotypes of Balechina pachydermata (Kofoid & Swezy) Loeblich & A.R. Loeblich, which Kofoid and Swezy (1921) described as several separate species (Gómez et al, 2015). Taylor (1980) reported that Kofoid and Swezy (1921) illustrated C. miniatum upside down, with incorrect flagellar details.…”

“…Both species are similar in diagnostic characters such as longitudinal striae, the central nucleus surrounded by a capsule, and the refractile bodies and vacuoles (Hansen and Daugbjerg, 2004). These characteristics are also present in other unarmored phagotrophic dinoflagellates such as Cucumeridinium F. Gómez, P. Lopez-Garcia, H. Takayama & D. Moreira and Lebouridinium F. Gómez, H. Takayama, D. Moreira & P. Lopez-Garcia (Gómez et al, 2015, 2016). Only species such as Gyrodinium spirale reached cell sizes similar to that of C. strangulatum.…”

“…The presence and type of eyespot are more stable diagnostic characters. A highly elaborated eyespot is characteristic of the warnowiid dinoflagellates that form a monophyletic group (Gómez et al, 2009; Reñe et al, 2013b, 2015), and the type of eyespot is a stable diagnostic character used to differentiate among different clades of woloszynskioid dinoflagellates (Daugbjerg et al, 2014). At present, this study can only transfer into Margalefidinium the photosynthetic species of Cochlodinium with an eyespot and an anterior nucleus.…”

Morphological and molecular characterization of Ptychodiscus noctiluca revealed the polyphyletic nature of the order Ptychodiscales (Dinophyceae)

“…The species of Balechina have been recently split into two genera, Balechina with thick double‐layer cell covering with bossed surface and Cucumeridinium with well‐marked longitudinal ridges (Gómez et al. ). Balechina , Cucumeridinium, and Ptychodiscus are distantly related among each other in the SSU rDNA molecular phylogeny (Fig.…”

“…, Gómez et al. , Mertens et al. ), the lack of molecular data of Ptychodiscus , the type of the order Ptychodiscales, renders it impossible to clarify the phylogenetic relationships within the Ptychodiscales.…”