Genus (Ehrenberg, 1830): Spheroidal; cytoplasm vacuolated, especially ectoplasm; nucleus central; one to many contractile vacuoles; axopodia straight, axial filaments terminate at surface of the nucleus (Kudo, 1966). Species: Ectoplasm vacuolated; a large central nucleus; diameter average 40-50 μm (Kudo, 1966).