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 result of two single segments fused together. Most millipedes have very elongated cylindrical or flattened bodies with more than 20 segments, while pill millipedes are shorter and can roll into a ball. Although the name "millipede" derives from the Latin for "thousand feet", no species was known to have 1,000 or more until the discovery of Eumillipes persephone, which can have over 1,300 legs. There are approximately 12,000 named species classified into 16 orders and around 140 families, making Diplopoda the largest class of myriapods, an arthropod group which also includes centipedes and other multi-legged creatures.
Gonopods are specialized appendages of various arthropods 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. In crustaceans and millipedes, gonopods are modified walking or swimming legs. 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.
Harpaphe haydeniana, commonly known as the yellow-spotted millipede, almond-scented millipede or cyanide millipede, is a species of polydesmidan ("flat-backed") millipede found in the moist forests along the Pacific coast of North America, from Southeast India to California. The dark coloration with contrasting yellow-tipped keels warn of its ability to exude toxic hydrogen cyanide as a defense. Despite the various common names given the species, the coloration pattern, cyanide defense, and associated almond scent occur in other flat-backed millipedes around the world.
Spirobolida is an order of "round-backed" millipedes containing approximately 500 species in 12 families. Its members are distinguished by the presence of a "pronounced suture that runs "vertically down the front of the head". Most of the species live in the tropics, and many are brightly coloured. Mature males have two pairs of modified legs, the gonopods, consisting of the 8th and 9th leg pair: the posterior gonopods are used in sperm-transfer while the anterior gonopods are fused into a single plate-like structure.
Mammamia profuga is a species of cave-dwelling millipede in the family Julidae. The only known species of the genus Mammamia, it was described in 2011 from a specimen discovered in a cave in Italy.
Polydesmida is the largest order of millipedes, containing approximately 3,500 species, including all the millipedes reported to produce hydrogen cyanide (HCN).
Julida is an order of millipedes. Members are mostly small and cylindrical, typically ranging from 10–120 millimetres (0.39–4.72 in) in length. Eyes may be present or absent, and in mature males of many species, the first pair of legs is modified into hook-like structures. Additionally, both pairs of legs on the 7th body segment of males are modified into gonopods.
Ommatoiulus is a genus of millipedes in the family Julidae.
Polyxenida is an order of millipedes readily distinguished by a unique body plan consisting of a soft, non-calcified body ornamented with tufts of bristles – traits that have inspired the common names "bristly millipedes" or "pincushion millipedes". There are at least 86 species in four families worldwide, and are the only living members of the subclass Penicillata.
Callipodida is an order of millipedes containing around 130 species, many characterized by crests or ridges.
Chordeumatida is a large order of millipedes containing some 1200 species with a nearly worldwide distribution. Also known as "sausage millipedes," they possess around 30 body segments behind the head as adults and reach about 25 mm (0.98 in) in length.
Branneria is a genus of small millipedes in the order Chordeumatida and the only genus in the family Branneriidae. Individuals reach about 4 mm (0.16 in) long. There are two species known, found in the southeastern USA: Branneria bonoculus is found in Arkansas and eastern Texas while B. carinata occurs from North Carolina to Florida and Mississippi. The adult B. bonoculus millipede has 28 body segments, and the adult B. carinata millipede has 26, both fewer than the 30 usually found in the order Chordeumatida. In both species, the gonopod complex in adult males includes three leg pairs rather than just the two that are usually modified into gonopods in this order.
Paeromopus is a genus of large cylindrical millipedes endemic to the U.S. state of California. All species exceed 10 centimeters in length, and the largest, P. paniculus, reaching 16.5 cm is the longest millipede species in North America. The genus was named by German entomologist Ferdinand Karsch in 1881 and contains four species: three occupying small ranges in the Sierra Nevada mountains and one occupying a large range including the Sierra Nevada and much of Northern California to the Central Coast.
Paeromopus paniculus is a species of millipede endemic to the Sierra Nevada mountains in the United States state of California. Reaching up to 16.5 centimeters in length, it is the longest known millipede in North America.
The Archidesmida is an extinct order of millipedes known from fossils from the Devonian period of Europe and North America. Archidesmidans have broad flat keels (paranota) extending from their body segments, and a modified pair of legs on the 8th segment that may have been involved in mating, similar to the gonopods of living millipedes which insert sperm into females. Alternately, the modified legs may have been used to grasp onto partners during mating.
Brachycybe (Greek for "short head") is a genus of andrognathid millipedes with species in the United States and East Asia. In a rare example of paternal care in invertebrates, males of most species guard the eggs until they hatch.
Titanophyllum spiliarum is a species of cave-dwelling millipede in the family Julidae. The only known species of the genus Titanophyllum, it was described in 2011 from specimens discovered in a cave in Greece. It has several unusual characteristics including eyelessness and a small hook on its hind-most body section that may be involved in keeping the animal ‘locked’ when it coils-up defensively.
Juliformia is a taxonomic superorder of millipedes containing three living orders: Julida, Spirobolida, and Spirostreptida, and the extinct group Xyloiuloidea known only from fossils.
Paeromopus angusticeps is a species of millipede found in the U.S. state of California. It occupies the largest geographic range of all four species of Paeromopus, occupying much of Northern California in a large arc extending from Monterey County on the central coast, north along the Coast Ranges to Humboldt County, and descending along the Cascades and Sierra Nevada range of eastern California. P. angusticeps is largely absent from California's Central Valley.
Hoffmaneumatidae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have only 28 segments, not the 30 segments usually found in this order. Adult males in this family feature a reduced leg pair 10 in addition to the two pairs normally modified into gonopods in this order. In the adult male of the species Hoffmaneuma exiguum, for example, the gonopod complex derives from all three leg pairs rather than from just the usual two.
