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.
Symphylans, also known as garden centipedes or pseudocentipedes, are soil-dwelling arthropods of the class Symphyla in the subphylum Myriapoda. Symphylans resemble centipedes, but are very small, non-venomous, and only distantly related to both centipedes and millipedes. They can move rapidly through the pores between soil particles, and are typically found from the surface down to a depth of about 50 centimetres (20 in). They consume decaying vegetation, but can do considerable harm in an agricultural setting by consuming seeds, roots, and root hairs in cultivated soil.
Myriapods are the members of subphylum Myriapoda, containing arthropods such as millipedes and centipedes. The group contains about 13,000 species, all of them terrestrial.
Polydesmida is the largest order of millipedes, containing approximately 3,500 species, including all the millipedes reported to produce hydrogen cyanide (HCN). Polydesmids grow and develop through a series of moults, adding segments until they reach a fixed number in the adult stage, which is usually the same for a given sex in a given species, at which point the moulting and the addition of segments and legs stop. This mode of development, known as teloanamorphosis, distinguishes this order from most other orders of millipedes, which usually continue to moult as adults, developing through either euanamorphosis or hemianamorphosis.
Xystodesmidae is a family of millipedes. Its members often have very small distributional areas, with many species only known from a single locality. They are found across the northern hemisphere, with peak diversity in the Appalachian Mountains, where one-third of the 300 or so species occur. They are particularly abundant in deciduous broadleaf forests in the Mediterranean Basin, Africa, Asia, Central and North America, and Russia. Information on basic taxonomy is scant for this family; for example, it is estimated that the genus Nannaria contains over 200 species, but only 25 were described as of 2006. By 2022, 78 species in Nannaria have been described.
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. Also known as slug millipedes, glomeridesmidans are small and somewhat flattened, and unlike other orders of Pentazonia, are unable to roll into a ball. Ocelli (eyes) are absent.
Chordeumatida is a large order of millipedes containing some 1200 species with a nearly worldwide distribution. Also known as sausage millipedes, they grow and develop through a series of moults, adding segments until they reach a fixed number in the adult stage, which is usually the same for a given sex in a given species, at which point the moulting and the addition of segments and legs stop. This mode of development, known as teloanamorphosis, distinguishes this order from most other orders of millipedes, which usually continue to moult as adults, developing through either euanamorphosis or hemianamorphosis.
The greenhouse millipede, also known as the hothouse millipede, short-flange millipede, or garden millipede, is a species of millipede in the family Paradoxosomatidae that has been widely introduced around the world, and is sometimes a pest in greenhouses.
Polydesmidae is a family of millipedes in the order Polydesmida. These millipedes range from 4 mm to 30 mm in length. This family includes species notable for featuring sexual dimorphism in segment number: Adult females in the genus Perapolydesmus have the usual 20 segments, but the adult males have only 19.
Glomeridesmidae, is a millipede family of the order Glomeridesmida. This family includes two genera: The genus Glomeridesmus includes most species in this family; the genus Glomeridesmoides includes one species.
Cleidogonidae is a family of millipedes in the order Chordeumatida. Adult millipedes in this family have 28, 29, or 30 segments. This family includes the genus Tianella, notable for featuring adult millipedes with 29 segments, a number not found in the adults of any other chordeumatidan species. All Tianella species have adults with 29 segments except for two in which adults have only 28 segments. In the Tianella species with 29 segments, adult females have 48 pairs of legs, as one would expect in adult female chordeumatidans with one segment fewer than the 30 usually found in this order. There are seven genera and at least 140 described species in Cleidogonidae.
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 only 19 segments as adults, one fewer than found in most polydesmid species. Accordingly, adults in this genus have two fewer legs than most polydesmid adults have: Females have only 29 pairs of legs, and males have only 28 pairs of walking legs, excluding one pair of gonopods. Species in this genus arrive at these lower numbers of legs and segments by going through the same stages of teloanamorphosis observed in other polydesmids but reaching maturity one moult earlier.
Chordeumatidae is a family of millipedes belonging to the order Chordeumatida. These millipedes range from 7 mm to 18 mm in length and are found in Europe. Adult millipedes 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. With the more extensive modifications to the legs in this family, species with the usual 30 segments feature adult females with only 49 leg pairs and adult males with only 45 pairs of walking legs, and species with only 28 segments feature adult females with only 45 leg pairs and adult males with only 41 pairs of walking legs.
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 range from 4.5 mm to 12 mm in length and have either 28 or 30 segments. For example, Orobainosoma hungaricum orientale, a subspecies of Haasea hungarica, has only 28 segments in adults rather than the 30 usually found in chordeumatidan adults, with only 46 pairs of legs in adult females and only 44 pairs of walking legs in adult males.
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.
Kashmireumatidae is a small family of millipedes belonging to the order Chordeumatida. These millipedes range from 5 mm to 14 mm in length and are found in East Asia. Adult millipedes in this family have only 26 or 28 segments rather than the 30 segments usually found in this order. In the species Vieteuma topali, adults have 26 segments, whereas in all other species in this family, adults have 28 segments.
Polyzonium germanicum, also known as the Kentish pinhead or boring millipede is a species of millipede within the family Polyzoniidae.
