Abstract

A new species of the genus Diplopsalopsis, D. kisselevii sp. nov., was found in Amursky Bay off the northwestern coast of the Sea of Japan. This species combines the Diplopsalopsis plate pattern with a protoperidinoid shape. The plate tabulation is Po, X, 3′, 2a, 7″, 4c, 4s, 5′″, 2″″. Cells are oval or almost rounded, slightly longer than wide and slightly flattened dorso-ventrally, 34–48 μm long and 34–46 μm wide. The length/width ratio is 1.0–1.05. The epitheca is slightly shorter than the hypotheca. The cingular list is very narrow, smooth and without ribs. The left sulcal list is narrow and short. The apical sunken depression of the theca contains the comma-like pore complex. Two intercalary plates are present. The narrow, long and hexagonal 1a contacts the 2′, 1″, 2″, 3″, 4″, and 2a plates. The large pentagonal 2a is positioned on the dorsal side of the epitheca with no contact to the Po plate. Diplopsalopsis kisselevii sp. nov. is similar to D. latipeltata in cell shape, and possesses reduced cingular and left sulcal lists and a long intercalary plate. However, D. kisselevii can be differentiated from D. latipeltata by the structure of the theca, the tabulation formula of the epitheca, and the shape, size and position of the anterior intercalary 1a plate.