gonopore

{{short description|Invertebrate genital pore}}

{{distinguish|Gonophore}}

File:Lobster_10.jpg, a member of the class Malacostraca. The gonopores are at the bases of the third walking leg, pointing towards the animal's tail.]]

A gonopore, sometimes called a gonadopore, is a genital pore in many invertebrates. Hexapods, including insects, have a single common gonopore, except mayflies, which have a pair of gonopores.{{cite book |author=Nikita Kluge |year=2004 |title=The Phylogenetic System of Ephemeroptera |publisher=Springer |isbn=978-1-4020-1974-6 |chapter=Morphology of mayflies |pages=21–54 |chapter-url=https://books.google.com/books?id=ly3961D_xdsC&pg=PA41}} More specifically, in the unmodified female, it is the opening of the common oviduct, and in the male, it is the opening of the ejaculatory duct.

The position of the gonopore varies considerably between groups, but is generally constant within groups, allowing its position to be used as a "segmental marker". In Malacostraca, it is on the sixth thoracic segment; in Symphyla, it is on the fourth trunk segment; in arachnids, it is on the second segment of the opisthosoma.{{cite book |editor=Richard A. Fortey |year=2003 |title=Trilobites and their Relatives: Contributions from the Third International Conference, Oxford 2001 |series=Issue 70 of Special Papers in Palaeontology |publisher=Wiley-Blackwell |isbn=978-0-901702-81-4 |chapter=Tagmata and segment specification in trilobites |pages=31–43 |author=Alessandro Minelli, Giuseppe Risco & Nigel Hughes |chapter-url=https://books.google.com/books?id=2E2fDXCkUEkC&pg=PA35}} In insects and centipedes, the gonopores are close to the animal's tail, while in millipedes, they are on the third body segment behind the head, near the second pair of legs.{{cite book|last1=Hopkin|first1=Stephen P.|last2=Read|first2=Helen J.|title=The Biology of Millipedes|date=1992|publisher=Oxford University Press|location=Oxford|isbn=0198576994}}