A new benthic dinoflagellate Spiniferodinium palauense sp. nov. (Dinophyceae) from Palau

A new benthic dinoflagellate Spiniferodinium palauense Horiguchi, Hayashi, Kudo & Hara sp. nov. is described from the marine lake, Uet era Ongael, on Ongael Island, Koror, Republic of Palau. The genus Spiniferodinium is unique in that the benthic non-motile formpossesses a helmet-shaped cell covering, termed the 'helmet shell', which is rigid, transparent and covered in many small regularly-distributed spines and covers the entire protoplasm. The dinoflagellate reproduces asexually by the formation of Gymnodinium-like motile cells within the helmet shell. The released motile cells directly return to the non-motile state by forming the helmet shell. The dinoflagellate from Palau is the second species for the genus and shares these characteristics. However, the new species is distinguished from the type species, Spiniferodinium galeiforme, in having a thinner cell body, a smaller epicone, a right-handed cingulum and a different type of spine on the shell. Phylogenetic analyses based on small subunit ribosomal RNA gene (SSU rDNA) sequences indicated that Spiniferodinium galeiforme and Spiniferodinium palauense formed a strongly-supported clade, suggesting these are closely related. However, Their SSU rDNA sequences differ by 22 base pairs, indicating they are distinct species. Our phylogenetic tree suggests that these unique benthic dinoflagellates evolved within the Gymnodinium clade sensu stricto.