(Busch, 1851)
Trunk up to 2.2 mm long, rectangular and flattened, with 2 conic appendices on its genital end (Fritillarinae-trunk). Mouth with protruding upper lip. Digestive tract axis transverse. Gonads asymmetrically arranged. Testis on the right side of the body; cylindrical and transverse in young specimens, later becoming Y-shaped. Ovary spherical, on the left side of the body. Tail musculature broad (Fritillarinae-tail). Two amphichordal cell on each side, with ejective ducts.