Family: Unicells or cells loosely attached forming 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: Cell body long, with a constriction at its center; each half-cell laterally straight or wavy; rings of spines at each peak of the waves (similar to Pleurotaenium nodosum or P. kayei); 2-4 arm-like projections at each ends; chloroplasts consisting of a central rod and radial laminae; pyrenoids aligned at the rod (Illustrations of The Japanese Fresh-water Algae, 1977).

T. gracile 4 clip 363 μm Japan, 1998