cloaca, in biology, enlarged posterior end of the digestive tract of some animals. The cloaca, from the Latin word for sewer, is a single chamber into which pass solid and liquid waste materials as well as the products of the reproductive organs, the gametes. Cloacas are found in amphibians, reptiles, birds, and lower mammals; higher mammals have a separate rectal outlet, the anus. The term cloaca is also used for analogous chambers in many invertebrates, such as worms of the phylum Nematoda.