Morphology and taxonomy of five marine sand-dwelling Thecadinium species (Dinophyceae) from Japan, including four new species:: Thecadinium arenarium sp nov., Thecadinium ovatum sp nov., Thecadinium striatum sp nov and Thecadinium yashimaense sp nov.

Thecadinium inclinatum Balech and four new marine sand-dwelling species of the dinoflagellate genus Thecadinium are described from the sandy beaches along the coast of Shikoku, Japan. Thecadinium inclinatum is thecate, bilaterally flattened, elliptical in shape, non-photosynthetic, and measures 55-75 mum in length and 43-59 mum in depth. The epi- and hypotheca theca are semielliptical and the thecal surface is smooth with small pores. The plate formula is Po (pore plate), 3', 7",?c,?s, 5"', 1"". Thecadinium ovatum sp. nov. is thecate, non-photosynthetic, bilaterally flattened and almost oval in lateral view. The cell measures 40-50 mum in length and 33-40 mum in depth. The hypotheca has two or three strong antapical spines. The plate formula is 3', 6",6c, 5s?, 5"', 1"". Thecadinium striatum sp. nov. is thecate, non-photosynthetic, bilaterally flattened and somewhat elliptical in lateral view. The cell is 33-41 mum long and 23-30 mum deep. Several striae are present on the hypotheca. The plate formula is 3', 6", 6c, 5s?, 5"', 1"". Thecadinium yashimaense sp. nov. is bilaterally flattened, photosynthetic and elliptical in ventral view. The cell is 44-65 mum long and 23-36 mum wide. The thecal surface is smooth with small pores. The cingulum forms a steep left-handed spiral. The plate formula is Po, 3', 1a, 6", 5c, 4s, 5"', 1"". Thecadinium arenarium sp. nov. is somewhat wedge-shaped in ventral view, photosynthetic with brownish chloroplasts and almost rounded in cross section. The cingulum forms a steep left-handed spiral. The cell measures 35-41 mum in length and 25-30 mum in width. The thecal surface is weakly reticulated with small pores. The hypotheca is conical. The plate formula is Po, 3', la, 6", 5c, 4s, 5"', 1"".