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 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.
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.
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.
Urochordeuma is a genus of millipedes in the order Chordeumatida and the only genus in the family Urochordeumatidae. Adult millipedes in this family have 30 segments. The two species are known from the U.S. state of Washington, where U. bumpusi is known from Pierce County, and U. porona from King County.
Haplogona is a genus of chordeumatidan millipedes and the only genus in the family Verhoeffiidae. Adult millipedes in this family have 30 segments. These species occur in the southern Alps of Europe, from Genoa, Italy to the Istrian peninsula.
Tetramerocerata is an order of pauropods containing 12 different families and about 480 different species. Tetrameroceratans have a 12 segmented body, 4 segmented antennae, 6 tergites, and 8 to10 legs pairs of legs as adults. Most pauropods in this order have 9 leg pairs as adults, but four genera have only 8 pairs, and adult females in the genus Decapauropus have either nine or ten pairs of legs. Pauropods in this order are generally 0.5 mm to 2 mm long, and are usually white or brown. Tetramerocerata has a subcosmopolitan distribution, occurring nearly worldwide.
Anthroleucosomatidae is a family of millipedes in the order Chordeumatida. These millipedes range from 3.5 mm to 28 mm in length. Adult millipedes in this family have 26, 28, 30, or 31 segments. This family includes Metamastigophorophyllon martensi, notable as the only chordeumatidan species with 31 segments. There are about 38 genera in Anthroleucosomatidae.
Metopidiotrichidae is a family of millipedes in the order Chordeumatida. These millipedes range from 4 mm to 17 mm in length. Adult millipedes in this family have 32 segments, not the 30 segments usually found in this order. Adult males in this family often feature a reduced or vestigial leg pair 10 as part of the gonopod complex, in addition to the two leg pairs typically modified into gonopods in this order. There are about 9 genera and at least 70 described species in Metopidiotrichidae.
Brachydesmus is a genus of millipedes belonging to the family Polydesmidae. Millipedes in this genus are found mainly in Europe. Species in this genus have 19 segments as adults. Adult females have 29 pairs of legs, and adult males have 28 pairs of walking legs, excluding one pair of gonopods.
Mastigophorophyllidae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have 30 segments.
Speophilosomatidae is a family of millipedes belonging to the order Chordeumatida. These millipedes are found in Japan and range from 4 mm to 6 mm in length. Adult millipedes in this family are notable for being among the few in this order with only 26 segments instead of the 30 usually found in chordeumatidans. The adult males in this family are also notable for involving three leg pairs in the gonopod complex rather than the two pairs typically modified into gonopods in this order.
Peterjohnsiidae is a small family of millipedes belonging to the order Chordeumatida. These millipedes range from 3 mm to 8 mm in length and are found in Australia. Species in this family exhibit sexual dimorphism in segment number: adult males have 30 segments, but adult females have 32 segments. In adult males in this family, the gonopod complex involves three leg pairs rather than just the two usually modified into gonopods in this order.
Haaseidae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have 28 or 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.
Haplobainosomatidae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have 30 segments.
Attemsiidae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have 30 segments.
Trachygonidae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have 28 or 30 segments.
Heterolatzeliidae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have 30 segments.
Opisthocheiridae is a family of millipedes belonging to the order Chordeumatida. These millipedes range from 5 mm to 16 mm in length and are found from Belgium to Morocco. Adult millipedes in this family have 26 or 30 segments. This family includes the species Opisthocheiron canayerensis, one of the few species in this order with only 26 segments.
