Morphology and phylogenetic affinities of Thecadinium foveolatum sp. nov. (Dinophyceae: Thecadiniaceae), a new marine benthic dinoflagellate from the west of Scotland

A new chloroplast-containing species of the sand-dwelling benthic dinoflagellate Thecadinium was isolated and cultured from a single cell collected from shallow waters of the marine Loch Ewe in North West Scotland. The cultured cells are described by light and scanning electron microscopy and the genetic affinities examined by comparison of ribosomal RNA gene sequences. Thecadinium foveolatum Bolch sp. nov. is heavily armoured with thecal plates that are ornamented with evenly distributed pores and contains numerous globular, dark golden-brown chloroplasts. Cells are broadly ovoid and slightly laterally compressed, with a descending cingulum displaced approximately half of the cell width. The thick thecal plates, numerous pores and the strongly displaced cingulum clearly differentiate this species from the only other chloroplast-containing species, T. kofoidii, and the remaining non-photosynthetic Thecadinium species described. Analysis of large-subunit rDNA sequences of Thecadinium foveolatum and other members of the Peridiniphycidae indicate that this new species is allied to the gonyaulacalean lineage rather than the peridinialean taxa included in the analyses.