LAUSR

A small armed dinoflagellate bloomed in the aquaculture ponds off the coast of Liaodong Bay, Bohai Sea of China, resulting in heavy mortalities of the cultured prawns (Penaeus japonicus) and larvae of Chinese mitten handed crabs (Eriocheir sinensis). The bloom-forming species was successfully isolated, and cellular morphology of the specimen was consequently investigated through light, fluorescent and electron microscopy. The small ((14.4±1.6) μm in length) ellipsoid cells show typical Heterocapsa thecal plate arrangement (Po, cp, 5′, 3a, 7′′, 6c, 5s, 5′′′, 2′′′′). The episome is evidently bigger than the hyposome. One to three spherical pyrenoids are located above or beside the large elongated nucleus. The body scale is characterized by a triangle basal plate with one central upright and nine peripheral spines. Above all, Heterocapsa bohaiensis could be distinguished from other Heterocapsa species by the combination of the cell size, morphology, cellular structure and body scale. Sequence analyses of both ITS and LSU regions reveal the significant genetic divergence between H. bohaiensis and other established species in this genus, further supporting novelty of this species. Noticeably, different sample treatment methods resulted in morphological variation of the apical pore complex (APC) of H. bohaiensis, which needs to be taken into account in future study.