Morphology and Molecular Phylogenetics of the Marine Sand-Dwelling Dinoflagellate Paramphidinium Jejuensis Gen. Et Sp. Nov. (Dinophyceae)

A new benthic unarmoured dinoflagellate, Paramphidinium jejuensis sp. nov. was isolated from Pyoseon Beach, Jeju Island, Korea, and is described here. The cells were observed using light, scanning and transmission electron microscopy. Phylogenetic analyses were conducted using partial SSU and LSU rDNA sequences. The species exhibits two forms, motile and sessile. Motile cells are oval, 26-35 & micro;m in length & times; 18-24 & micro;m in width, whereas sessile cells are larger, 35-38 & micro;m long & times; 27-30 & micro;m wide, with a round and broad shape. The episome is much smaller than the hyposome and becomes embedded within it in the non-motile (sessile) state. A distinct ventral pit occurs at the posterior end of the episome, and a small, shallow sulcus is located below the episome near the cell centre. The nucleus is spherical, located in the centre of the hyposome. The morphological features are most similar to Amphidinium mootonorum, but P. jejuensis can be distinguished by the shape of the nucleus, sulcus position and the shape of the episome when in a sessile state. The phylogenetic analyses of rDNA showed that P. jejuensis clearly differed from A. mootonorum and formed a clade with A. mootonorum separate from the Amphidinium sensu stricto group. This clade is significantly divergent from the other genera which belong to the Amphidiniales, Gymnodiniales and Ptychodiscales. These morphological and phylogenetic results allow us to establish a new genus Paramphidinium with Paramphidinium mootonorum (Sh.Murray & D.J.Patterson) comb. nov. as the type species and to describe Paramphidinium jejuensis gen. et sp. nov.https://zoobank.org/urn:lsid:zoobank.org:pub:9D521B2E-36A4-4902-887F-4F8C31427EF6