Genus: Colonies (coenobia) up to 1.5 mm diam.; many cells (500-60,000) in single layer; somatic cells identical, variable shape, with 2 outwardly directed flagella; asexual reproduction by formation of a daughter colony by loss of flagella and repeated division of a gonidium to produce a small hollow sphere of cells in which flagellar bases and nuclei are oriented inwards; before being released, daughter colony undergoes "inversion" turning inside out; flagella then form (Illustrated Guide, 1985).
Species: 5000-15,000 cells with cytoplasmic connections (Kudo, 1966). Cell body star-shaped, or amoeboid in shape, gelatinous matrix clearly separated from each other; colony consisting of 8000-17000 cells with a thick cytoplasmic connection.