Genus: Unicells or a colony of spherical cells covered with a distinct sheath. Species: Colonies consisting of many cells lacking definite layers; cells gathered at the center of the colonies; cell body (excluding sheath) larger than 6 μm in diameter (Illustrations of The Japanese Fresh-water Algae, 1977).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Tanohara marsh, Shiga highland, Yamanouchi town, Nagano Pref., Japan, June 1, 2006 by Y. Tsukii