Despite the name, it is not a true louse (which are insects), but rather is related to the skeleton shrimp, most species of which are found in shallower waters.

Whale lice are external parasites, found in skin lesions, genital folds, nostrils and eyes of marine mammals of the order Cetacea.

The body of a whale louse is distinctly flat and considerably reduced at the rear.

The whale louse Cyamus catodontis lives exclusively on the skin of the male, while Neocyamus physeteris is found only on females and calves.

[2] Whale lice attach themselves to the host body in places that protect them from water currents, so they can be found in natural body openings and in wounds; with baleen whales they are found primarily on the head and in the ventral pleats.