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. 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. although the terminology used to describe the same structures may vary between authors. The complex morphology of millipede gonopods may be driven by
sperm competition or other forms of
sexual selection, with some structures serving to scoop out or displace sperm of other males, and others acting to stimulate females into becoming sexually receptive. Millipede gonopods do not produce sperm directly, but rather gather sperm produced from a
gonopore on the base of the third body segment. Gonopods develop gradually during the growth of an individual. In early developmental stages, all legs are of the walking type, and cannot be used to determine sex. Through successive molts, the walking legs metamorphose into mature gonopods. ,
Blaniulidae). A: juvenile with walking legs on segment 7 (asterisk). B: subsequent stage with walking legs replaced by gonopod primordia. C: adult stage with gonopods (colored) in place of walking legs. ==See also==