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 tight ball. Although the name "millipede" derives from Latin for "thousand feet", no species was known to have 1,000 or more until the discovery in 2020 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.
Glomerida is an order of pill-millipedes found primarily in the Northern Hemisphere. Also known as northern pill millipedes, 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, with more than 5,000 species, including all the millipedes reported to produce hydrogen cyanide (HCN). This order is also the most diverse of the millipede orders in terms of morphology. Millipedes in this order are found in all regions of the world other than Antarctica.
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. These features have inspired the common names bristly millipedes or pincushion millipedes. This order includes about 148 species in four families worldwide, which represent the only living members of the subclass Penicillata.
Polyzoniida is an order of millipedes in the subterclass Colobognatha. This order contains three families and more than 70 described species. The species in this order are also known as camphor millipedes, because ozopore secretions in this order frequently have a strong camphor-like smell. Poison frogs in South America and Madagascar evidently obtain some of their poison from these millipedes.
Glomeridesmida is an order of millipedes in the infraclass Pentazonia containing two families and at least 35 described species. Glomeridesmida is the only living order of the superorder Limacomorpha. Glomeridesmidans are also known as slug millipedes.
Chordeumatida is a large order of millipedes containing more than 1,400 species. Also known as sausage millipedes, they are found nearly worldwide. Chordeumatida is the largest order in the superorder Nematophora, a group also known as spinning millipedes because their telsons feature spinnerets used to build nests of silk. These millipedes produce this silk to create chambers in which to molt or to lay their eggs.
Siphoniulus is a poorly known genus of millipede containing only two living species: S. alba from Indonesia, and S. neotropicus from Mexico and Guatemala. An additional two fossil species are known from Cretaceous amber. Siphoniulus species are the only members of the family Siphoniulidae and order Siphoniulida, making Siphoniulida the smallest millipede order. Few specimens are known, and their classification is contentious, although most recent studies place them as basal members of the Helminthomorpha.
Fuhrmannodesmidae is a family of millipedes belonging to the order Polydesmida. Although some authorities deem Fuhrmannodesmidae to be a junior synonym for Trichopolydesmidae, others still regard the taxonomic status of Fuhrmannodesmidae as valid. The family Fuhrmannodesmidae includes over 50 genera.
Trichopetalidae is a family of millipedes in the order Chordeumatida. Adult millipedes in this family have 28 or 30 segments. There are about 5 genera and at least 30 described species in Trichopetalidae.
Metopidiotrichidae is a family of millipedes in the order Chordeumatida. This family includes more than 70 species. These millipedes are found in Indochina, Australia, and on Pacific islands from New Zealand to Japan.
Brachychaeteumatidae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have 30 segments.
Vandeleumatidae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have 28 or 30 segments.
Chamaesomatidae is a family of millipedes belonging to the order Chordeumatida. This family contains 28 species distributed among 11 genera. These millipedes are found in Europe and North Africa.
Apterouridae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have 30 segments.
Pygmaeosomatidae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have 30 or 32 segments.
Adritylidae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have 30 segments.
Hoffmaneumatidae is a family of millipedes belonging to the order Chordeumatida. This family includes two genera, one (Hoffmaneuma) found in the Russian Far East and the other (Japanoparvus) found in Japan. Millipedes in this family range from 4 mm to 6 mm in length. 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.
Entomobielziidae is a family of millipedes belonging to the order Chordeumatida. This family includes 18 species, including 13 in the genus Tianella. Millipedes in this family are found in Romania, central Asia, and the Himalayas.
Opisthocheiridae is a family of millipedes belonging to the order Chordeumatida. This family includes 40 species distributed among seven genera. These millipedes are found in western Europe and Morocco.
