gonopore

A gonopore is the external opening of an organism’s reproductive tract through which gametes are released, received, or transferred. The exact anatomy and function of a gonopore vary widely across different groups, and not all species have a single, clearly defined gonopore. In many invertebrates such as some crustaceans and annelids, the gonopore is a distinct pore on the body surface, often located on the ventral side of the abdomen or thorax, serving as the outlet for eggs or the entry point for sperm during reproduction. In other species, especially those with a cloacal or shared exit for excretory and reproductive systems, a separate gonopore may be absent or not externally visible.

In hermaphroditic organisms, individuals may possess both male and female gonopores or may exchange sperm via specialized copulatory structures, with the gonopores acting as the sites for sperm transfer or egg release. The position, number, and surrounding structures of gonopores are often used in anatomical descriptions and can aid in the taxonomic differentiation of species, particularly in fossil groups where soft tissues are not preserved but exterior openings may be evident on exoskeletons or carapaces.

Etymology: the term derives from Greek gónos (seed, offspring) and poros (pore).