Cloaca

: cloacae (/kloʊˈeɪsi/ kloh-AY-see or /kloʊˈeɪki/ kloh-AY-kee), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals.

[8] Birds that mate using this method touch their cloacae together, in some species for only a few seconds, sufficient time for sperm to be transferred from the male to the female.

In lampreys and in some ray-finned fishes, part of the cloaca remains in the adult to receive the urinary and reproductive ducts, although the anus always opens separately.

In the embryo, the embryonic cloaca divides into a posterior region that becomes part of the anus, and an anterior region that develops depending on sex: in males, it forms the penile urethra, while in females, it develops into the vestibule or urogenital sinus that receives the urethra and vagina.

[13][19] However, some placentals retain a cloaca as adults: those are members of the order Afrosoricida (small mammals native to Africa) as well as pikas, beavers, and some shrews.

[20][21][22][23] Being placental animals, humans have an embryonic cloaca which divides into separate tracts during the development of the urinary and reproductive organs.

The constant flow of water through it has allowed various fish, polychaete worms and even crabs to specialize to take advantage of it while living protected inside the cucumber.

Cloaca of a red-tailed hawk
Cloaca of a female bird
Cloaca of a male bird
A roseate spoonbill excreting urine in flight
Diagrams to illustrate the changes in the cloaca in mammals during development. A , early embryonic stage, showing the cloaca receiving the urinary bladder, the rectum, and the Wolffian duct, as in non- therian vertebrates. B , later stage, showing the beginning of the fold which divides the cloaca into a ventral urogenital sinus which receives the urinary bladder , Wolffian ducts, and ureters , and into a dorsal part which receives the rectum . C , further progress of the fold, dividing the cloaca into urogenital sinus and rectum; the ureter has separated from the Wolffian duct and is shifting anteriorly. D , completion of the fold, showing complete separation of the cloaca into ventral urogenital sinus and dorsal rectum. [ 14 ]
Cloacal opening in an Australian brushtail possum