Larsen and Patterson, 1990. Cell outline is oval. Cells are 16 to 20 microns long, 8.5 to 13 microns wide, laterally compressed, and with two rows of extrusomes lying at the margin of the cell. Two flagella insert laterally and subapically in a depression on the right ventral side of the cell and are longer than the cell. The anterior flagellum may beat backwardly. In resting cells, the anterior flagellum is held to the left margin of the cell and the posterior flagellum is coiled up. The nucleus is located in the posterior part of the cell. The cells move rapidly by swimming and contained other algae as food.