Genus (Perty, 1849): Oral cavity large, over most of ventrum; oral cilia as 1 long polykinetid (Illustrated Guide, 1985). Oval; dorsal side convex, ventral side concave; cytostome 3/4 to 4/5 the body length; on its left with a large membrane composed of may ciliary rows; contractile vacuole in mid-dorsal region; macronucleus ellipsoid, subterminal; a micronuleus; caudal cilia (Kudo, 1966).
Species:

Lembadion lucens, x 100&200, x 400, x 640, Japan, 1998 by Y. Tsukii