Family: Unicells or cells loosely attached to form hyphae; cell body varied in shape, a constriction at the center in most species; cell walls consisting of two or more parts, with small pores and various ornaments (Illustrations of The Japanese Fresh-water Algae, 1977).
Genus: Variable in shape; strong constriction at center; semicell ellipsoidal, polygonal, etc.; cell wall with simple or branching spines, most of them laterally aligned; 4 plate-like chloroplasts in each semicell; one or more pyrenoids in each chloroplast (Illustrations of The Japanese Fresh-water Algae, 1977).

Xanthidium sp. 3 clips Hiroshima Univ. Hiroshima, 1998

Xanthidium sp. 1 clip Hiroshima Univ. Hiroshima, 1998