Diagnosis
provided by World Register of Marine Species
Original diagnosis by Ditlevsen (1917: 67), for the family Otopsidae: "Forms of medium size with the body of nereidiform or euniciform aspect, consisting of a considerable number of segments. Body somewhat flattened; the dorsal side only a little convex, the ventral side provided with a well marked, rather deep depression extending along the mid-ventral line through about the whole length of the animal. The cephalic lobe is well developed, its longitudinal axis forming about a right angle with the longitudinal axis of the body. Two tentacles (short and thick) are present; in the median line of the cephalic lobe is situated a rather small, unpaired tentacle (possibly a nuchal organ?). Pharynx longitudinally folded; chitinous jaws and paragnaths wanting. The parapodium is well developed, long, muscular and highly movable. Acicles present in two bundles, a ventral, consisting of 3, and a dorsal, consisting of 2 acicles. Dorsal and ventral cirrus developed, lamellifonn. Bristles uncompound, hairy, exceedingly delicate."
