Polydesmida is the largest order of millipedes, containing approximately 3,500 species, including all the millipedes reported to produce hydrogen cyanide (HCN).
Tridontomidae is a small family of millipedes. Its members are endemic to Guatemala. These millipedes range from 22 mm to 28 mm in length. This family includes the remarkable species Aenigmopus alatus, in which adult males feature no gonopods. This millipede is the only species in the infraclass Helminthomorpha without 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.
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.
Striariidae is a family of millipedes in the order Chordeumatida. Adult millipedes in this family have 30 segments. There are at least 3 genera and about 13 described species in Striariidae.
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.
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.
Haasiidae is a family of millipedes belonging to the order Chordeumatida. These millipedes range from 4.5 mm to 12 mm in length and are found in Europe. Adult millipedes in this family have 28 or 30 segments.
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.
Golovatchiidae is a family of millipedes belonging to the order Chordeumatida. This family contains a single species, Golovatchia magda. This species ranges from 15 mm to 17 mm in length and is found in the Russian Far East. Adult millipedes of this species have 30 segments. In the adult male of this species, the gonopod complex involves three leg pairs rather than just the two that are usually modified into gonopods this order.
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.
Lusitaniosomatidae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have 30 segments.
Heterolatzeliidae is a family of millipedes belonging to the order Chordeumatida. Adult millipedes in this family have 30 segments.
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. In some species, the second leg pair in the adult female is vestigial, but all other species in this family, the adult female has a normal legs.
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.
