Genus: Colony spherical; 8-16 cells of similar size, close together, mutually compressed; 2-layered gelatinous envelope; cells with 2 equal-length flagella; 2 contractile vacuoles anterior; nucleus central (Illustrated Guide, 1985).
Species: Cells 8-17 μm; colony 20-50 μm to 250 μm; 16 cells as a tight sphere within clear matrix (How to know the protozoa, 1979). Colony barrel-shaped, 8- or 16-celled; cells wedge-shaped; chloroplast longitudinally striated; colony 20-42 μm across, 60 μm long; cells 8-17 μm diam. (Illustrated Guide, 1985).