From the Latin cloaca, an underground channel for sewage.

The cloaca is an enlarged part of the rectum, opening outward with the cloacal opening (cartilaginous, bivalves). On the dorsal side of the cloaca is located urogenital sinus, which opens the ureters and reproductive ducts of cartilaginous fish. The wall of the cloaca is lined with multilayered epithelium. Among fish, only sharks, rays and bipedal fish have a cloaca.