Xystodesmidae is a family of millipedes in the suborder Leptodesmidea within the order Polydesmida. The family Xystodesmidae was created by the American biologist Orator F. Cook in 1895 and named after the genus Xystodesmus. This family includes more than 390 known species distributed among 62 genera. Many species, however, remain undescribed: 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.
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.
Anthroleucosomatidae is a family of millipedes in the order Chordeumatida. This family includes more than 100 species distributed among 40 genera. This family has a mostly Holarctic distribution, with the greatest diversity in the area around the Mediterranean sea.
Caseyidae is a family of millipedes in the order Chordeumatida. Adult millipedes in this family have 30 segments. There are about 7 genera and at least 40 described species in Caseyidae.
Rhiscosomides is a genus of millipedes in the order Chordeumatida with seven described species, and is the only genus in the family Rhiscosomididae. Adult millipedes in this family have 30 segments.
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.
Brachydesmus is a genus of millipedes belonging to the family Polydesmidae. The Czech zoologist Camill Heller first described this genus to contain the type species B. subterraneus. This genus now includes about 75 described species.
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.
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.
Peterjohnsiidae is a small family of millipedes belonging to the order Chordeumatida. The family was first described in 1987 by Jean-Paul Mauriès. 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.
Diplomaragnidae is a family of millipedes belonging to the order Chordeumatida. These millipedes range from 9 mm to 24 mm in length and are found from the Volga River region in Russia to Japan and Taiwan. All known adult females in this family have 32 segments rather than the 30 segments typically found in this order; in most species, adult males also have 32 segments, but in some species, adult males have only 30 segments.
Haaseidae is a family of millipedes belonging to the order Chordeumatida. This family includes 29 species. These millipedes are found in central and southeastern Europe.
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.
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.
Opisthocheiron canayerensis is a species of millipede in the family Opisthocheiridae. This species is found in France, far inside deep caves. This millipede is notable as one of only a few species in the order Chordeumatida with only 26 segments in adults, four fewer segments than typically found in adults this order.
Metamastigophorophyllon is a genus of millipedes in the family Anthroleucosomatidae. This genus includes millipedes found in Azerbaijan, Iran, Russia, and Georgia. All five species in this genus have 31 segments in adults. This genus is notable for including the only species in the order Chordeumatida with 31 segments rather than the 30 segments usually observed in adults in this order.
