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Gonopods are specialized
appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including ant ...
s of various
arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
s used in reproduction or egg-laying. In males, they facilitate the transfer of sperm from male to female during mating, and thus are a type of
intromittent organ An intromittent organ is any external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most non-mammalian aquatic species fertilize their eggs ...
. In
crustaceans Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gr ...
and
millipedes Millipedes are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derived from this feature. Each double-legged segment is a resu ...
, gonopods are modified walking or swimming legs. Gonopods may be highly decorated with elaborate structures which may play roles in
sperm competition Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and ...
, 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 An aedeagus (plural aedeagi) is a reproductive organ of male arthropods through which they secrete sperm from the testes during copulation with a female. It can be thought of as the insect equivalent of a mammal's penis, though the compariso ...
of insects or the penis of harvestmen.


Insects

In insects, gonopods are appendages of the genital segment that may be used in insemination, or that comprise the egg-laying apparatus.


Crustaceans

In male decapod
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...
s, gonopods are modified swimming appendages ( pleopods). The anterior two pair of pleopods in males are modified for sperm transferring, with differing degree of morphological diversification.


Millipedes

In
millipede Millipedes are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derived from this feature. Each double-legged segment is a re ...
s, 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 Pentazonia is a taxonomic infraclass of millipedes containing the pill-millipedes (Oniscomorpha) which can roll into a ball and the order Glomeridesmida which cannot. Defining traits (apomorphies) include divided sternites, a labrum with single ...
(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. The complex structure of gonopods is a primary method of distinguishing closely related species of millipede, 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 Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and ...
or other forms of
sexual selection Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex (in ...
, 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 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. More specifically, in the unmodified female it is the ...
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.


See also

* Gonopodium, a modified fin for sperm transfer found in some fish *
Clasper In biology, a clasper is a male anatomical structure found in some groups of animals, used in mating. Male cartilaginous fish have claspers formed from the posterior portion of their pelvic fin which serve to channel semen into the female's ...
s, pelvic fins modified for copulation in cartilaginous fish *
Pedipalp Pedipalps (commonly shortened to palps or palpi) are the second pair of appendages of chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to the chelicerae ("jaws") a ...
s, appendages of arachnids involved in sperm-transfer


References

{{reflist Arthropod anatomy Sex organs