Gonopod

Gonopods may be highly decorated with elaborate structures which may play roles in sperm competition, and can be used to differentiate and identify closely related species.

Gonopods generally occur in one or more pairs, as opposed to the single (un-paired) reproductive organs such as the aedeagus of insects or the penis of harvestmen.

The anterior two pair of pleopods in males are modified for sperm transferring, with differing degree of morphological diversification.

[3] In millipedes, gonopods consist of one or two pairs of often highly modified walking legs in mature males, and are primarily found in members of the subgroup Helminthomorpha—containing most orders and the vast majority of species—where they are located on the seventh body segment consisting of leg pairs 8 and/or 9.

[4] Males of the subgroup Pentazonia (which includes the Oniscomorpha (pill millipedes) and Glomeridesmida) lack gonopods but possess enlarged appendages known as telopods at the rear of the body used to firmly hold females during mating.