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: Many species; usually ovoid or elongate in shape; AZM 1/4 of the body length; two rows of ventral cirri; frontal cirri present (Carey, 1992). Frontventral cirri in zig-zag files; rear rounded, body oval to long (Illustrated Guide, 1985).