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.
Chilognatha is a subclass of the class Diplopoda, which includes the vast majority of extant millipede, about 12,000 species.
Glomerida is an order of pill-millipedes found primarily in the Northern Hemisphere. They superficially resemble pill-bugs or woodlice, and can enroll into a protective ball. They have twelve body segments, 17 to 19 pairs of legs, and males have enlarged rear legs involved in mating. The order includes about 30 genera and at least 280 species, including Glomeris marginata, the common European pill-millipede. The order contains members in Europe, South-east Asia and the Americas from California to Guatemala. Although historically considered closely related with the similar sphaerotheriidans that also enroll, some DNA evidence suggest they may be more closely related to glomeridesmidans, a poorly known order that does not enroll.
Polydesmida is the largest order of millipedes, containing approximately 3,500 species, including all the millipedes reported to produce hydrogen cyanide (HCN).
Sphaerotheriida is an order of millipedes in the infraclass Pentazonia, sometimes known as giant pill millipedes. They inhabit Southern Africa, Madagascar, South and Southeast Asia, Australia and New Zealand. Like the Northern Hemisphere pill millipedes of the order Glomerida, these millipedes can roll into a ball when disturbed. When they are rolled-up, most sphaerotheriidans reach a maximum size of a cherry or golf ball, but some species from Madagascar can even reach the size of an orange. When rolled-up, predators are unable to unravel giant pill millipedes since the margins of their second and last dorsal plates fit perfectly into one another, creating a sealed ball. A few giant pill millipede species are able to produce sound, the only millipedes known to do this. This order of millipedes is also unique in that some African species are used for medicinal purposes.
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.
Polyxenidae is a family of millipedes in the order Polyxenida containing approximately 47 species in 19 genera. Adults in all species in this family have 13 pairs of legs.
Glomeridesmida is an order of millipedes in the infraclass Pentazonia containing 2 families and at least 31 species. Glomeridesmida is the only living order of the superorder Limacomorpha. Glomeridesmidans are small and somewhat flattened, and unlike other orders of Pentazonia, are unable to roll into a ball. Ocelli (eyes) are absent.
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 and reach about 25 mm (0.98 in) in length.
Siphonorhinidae is a family of millipede in the order Siphonophorida. There are at least 4 genera and about 12 described species in Siphonorhinidae.
Stemmiulida is an order of millipedes consisting of approximately 130 species, reaching up to 50 mm in length. It contains a single family, Stemmiulidae.
Casimir Albrecht Willem Jeekel (1922–2010) was a Dutch myriapodologist and entomologist known for his major contributions to the taxonomy of millipedes. His 1971 monograph Nomenclator Generum et Familiarum Diplopodorum is credited as launching the "modern era" of millipede taxonomy, and has been considered the "most important single work ever published on the Diplopoda". He served as director of the Zoological Museum Amsterdam, and authored over 150 works on the taxonomy of millipedes and other myriapods.
Ammodesmidae is a family of small millipedes endemic to Africa, containing seven species in two genera. Ammodesmids range from 1.4 to 5.0 mm long with 18 or 19 body segments in both sexes, and are capable of rolling into a tight sphere.
Glomeris klugii is a species of pill millipedes.
Synxenidae is a family of bristly millipedes (Polyxenida). Three genera and around 10 species are known. Adult synxenids possess 15 or 17 pairs of legs, with the last two pair modified for small jumps. Adults in most species in this family have 17 pairs of legs, but in two species, they have only 15 pairs of legs.
Bollmania is a genus of millipedes with around six species occurring from Central through East Asia, including Iran, Pakistan, Tajikistan, and China. The genus was established by entomologist Filippo Silvestri in 1896, and is named in honor of Charles Harvey Bollman. Bollmania is the sole genus of the family Caspiopetalidae.
Lophoproctidae is a family of millipedes in the order Polyxenida containing approximately 65 species in 6 genera.
Hyperglomeris is a genus of diplopods in the family Glomeridae.
Chordeumatidae is a family of millipedes belonging to the order Chordeumatida. Species in this family have either 28 or 30 segments. This family features distinctive sex-linked modifications to the legs in adults: In the adult female, a legless sternite replaces the third pair of legs, and in the adult male, five pairs of legs are modified in the gonopod complex. These modifications are more extensive than those found in other adult males in this order, which often have only two leg pairs modified into gonopods.
