Family: Frontal cirri differ in size and/or pattern from ventral ones of files;
"collar" extends short distance along right edge of body; oral area not U-shaped
(Illustrated Guide, 1985).
Genus: With 2 or more right marginal files of cirri (Illustrated Guide, 1985). Ellipsoid; flexible; posterior rounded; flattened ventral surface with 4-10 rows of cirri; 2 marginal rows; 3 or more frontals; 5-12 anals (Kudo, 1966). Ovoid to elongate with large number of ventral rows of cirri (files); transverse cirri present; frontal cirri undifferentiated from ventrals (Carey, 1992).