Cloaca
- For other meanings, see Cloaca (disambiguation)
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, urinary, and genital tracts of certain animal species. The word comes from Latin, and means "sewer". All birds, reptiles, and amphibians possess this orifice, by which they simultaneously evacuate both urine and feces. Monotremes also possess one. In contrast, each individual among most species of placental mammals and bony fishes has, in lieu of a cloaca, a specialized opening for at least one of these tracts.
Excretory systems with analogous purpose in certain invertebrates are also sometimes referred to as "cloacae".
In birds the reproductive system must be regrown prior to the mating season of each species. Such regeneration usually takes about a month. Birds generally produce one batch of eggs per year, but they will produce another batch if the first is taken away (they have the ability to produce more). Some birds, such as some species of swans and ducks, do not use the cloaca for reproduction, but have a penis.
The cloacal region is also often associated with a secretory organ, the cloacal gland, which has been implicated in the scent marking behaviour of some reptiles, amphibians and monotremes.
Some turtles, especially those specialized in diving, are highly reliant on cloacal respiration during dives. [1] They accomplish this by having a pair of accessory air bladders connected to the cloaca which can absorb oxygen from the water. [2][3]