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.
Eutrichodesmus is a genus of millipedes in the family Haplodesmidae, containing at least 32 species in China, Taiwan, and Southeast Asia. One of these species exhibits sexual dimorphism in segments number: The adult females have 20 segments, but the adult males have only 19.
Motyxia is a genus of cyanide-producing millipedes that are endemic to the southern Sierra Nevada, Tehachapi, and Santa Monica mountain ranges of California. Motyxias are blind and produce the poison cyanide, like all members of the Polydesmida. All species have the ability to glow brightly: some of the few known instances of bioluminescence in millipedes.
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.
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.
Brachoria is a genus of polydesmidan millipedes in the family Xystodesmidae inhabiting the Eastern United States. Also known as the Appalachian mimic millipedes, at least 30 species are known, with highest diversity in the Appalachian Mountains, especially the Cumberland Plateau and Ridge and Valley Province.
Platyrhacidae is a family of polydesmidan millipedes distributed in Southeast Asia and tropical Central and South America.
Xystocheir is a genus of millipedes in the family Xystodesmidae. The genus is endemic to California in the United States, where it is distributed in the Coast Ranges and the Sierra Nevada.
Parafontaria is a genus of "flat-backed" millipedes consisting of 13 species native to Japan, where they are referred to as train millipedes. This is because some species exhibit periodical swarming behavior during which large numbers congregate and can impact train passage when this congregation occurs on tracks. Documentation of this event goes back to 1920. Individuals vary from around 3.5 to 6 cm as adults, and feed on leaf litter as well as soil, making them comparable to earthworms in facilitating decomposition and soil nutrient cycling.
Haplodesmidae is a family of millipedes in the order Polydesmida. Species occur in East Asia, Southeast Asia, and Oceania, although some species have been introduced to the New world tropics. Species are small bodied, often with elaborate sculpturing on the tergites, and some species are capable of rolling into a near-complete ball.
Apheloria tigana, known as the Yellow-and-black flat millipede, is a large North American flat-backed millipede in the family Xystodesmidae. It is reported to secrete cyanide compounds as a defense. It is recommended that one wash hands after handling this organism as the toxic compounds it secretes are poisonous and can cause extreme irritation if rubbed in the eyes.
Apheloria is a genus of flat-backed millipedes in the family Xystodesmidae, occurring in the central and southeastern United States, and ranging as far north as southern Quebec, Canada. They are aposematically colored in black and contrasting reds and yellows, and some species in the Appalachian Mountains resemble species of Brachoria where they co-occur, a phenomenon known as Müllerian mimicry.
Fuhrmannodesmidae is a family of millipedes belonging to the order Polydesmida. The family includes over 50 genera. This family includes three species notable for being among the very few species in this order to feature adults with only 18 segments rather than the 20 segments usually found in polydesmids. This family also includes several genera notable for featuring sexual dimorphism in segment number: adult females in these genera have the usual 20 segments, but adult males have only 19. Millipedes in these species arrive at these lower numbers of segments by going through the same stages of teloanamorphosis observed in other polydesmids but reaching maturity one moult earlier for 19 segments or two moults earlier for 18 segments.
Brachoria dentata, the Pennington Gap mimic millipede, is an Appalachian mimic millipede in the Xystodesmidae family.
Pleuroloma flavipes, commonly known as the traveling cherry millipede, is a species of flat-backed millipede in the family Xystodesmidae. It has the widest distribution of any species of xystodesmid millipede and is found in eastern North America from southeastern North Dakota, eastward to Connecticut, and southward to North Carolina, northern Louisiana, and southern Texas. Pleuroloma flavipes millipedes are occasionally observed in large aggregations of individuals where they appear to move en masse in a certain direction, hence the common name "wandering cherry millipede". In a report from 1950, an aggregation of about 6,000 individuals were encountered on a single bridge at McCormick's Creek State Park, Indiana. The species is extremely variable in coloration, and converges in appearance with several species of Apheloria and Brachoria as a result of mimicry.
The genus Nannaria, commonly known as twisted-claw millipedes, is a genus of millipedes in the family Xystodesmidae first described by Ralph Chamberlin in 1918. In 2022, entomologists Derek Hennen, Jackson Means and Paul Marek discovered and described 17 new species, which expanded the size of Nannaria to 78, making it the largest genus of Xystodesmidae.
Cherokia Chamberlin, 1949 is a genus consisting of a single species, Cherokia georgiana. Commonly known as the wrinkled flat-backed millipede, this species belongs to the order Polydesmida and the family Xystodesmidae. It inhabits forests in the southeastern United States, particularly those with hemlock, maple, tulip poplar, rhododendron, cedar, and spruce-fir trees.
Trichopolydesmidae is a family of millipedes belonging to the order Polydesmida. This family includes two genera notable for featuring sexual dimorphism in segment number: adult females in these genera have the 20 segments usually found in this order, but adult males have only 19. This family also includes the species Deharvengius bedosae, notable for being among the very few species in this order to feature adults with only 18 segments rather than the 20 segments usually found in polydesmids.
Nannaria swiftae, also known as the Swift twisted-claw millipede or Taylor Swift's millipede, is a species of millipede in the family Xystodesmidae. It is found only in the Appalachian mountains of the U.S. state of Tennessee. It was discovered and described in 2022 by entomologists Derek Hennen, Jackson Means and Paul Marek, who expanded the genus Nannaria to 78 species. They named the species in honor of American singer-songwriter Taylor Swift.
