The archinephros, or holonephros, is a primitive kidney that has been retained by the larvae of hagfish and some caecilians.[1] A recent author has referred to this structure as "the hypothetical primitive kidney of ancestral vertebrates".[2] In the earliest vertebrates, this structure potentially extended the entire length of the body and consisted of paired segmental structures which drained via a pair of archinephrenic ducts into the cloaca. The entire structure arises from the nephric ridge, which in higher animal embryos gives rise to nephrotomes and the pronephroi at around 4 weeks gestation in humans.[3] The pronephroi are supplanted by mesonephroi and finally by definitive kidneys, the metanephroi, by around 5 weeks gestation. The archinephros is nonfunctional in humans and other mammals.[4]
The three types of mature vertebrate kidneys develop from the archinephros: the pronephros from the front section, the mesonephros from the mid-section and the metanephros from the rear section.[5]