Pill millipedes are any members of two living orders of millipedes, often grouped together into a single superorder, Oniscomorpha. The name Oniscomorpha refers to the millipedes' resemblance to certain woodlice (Oniscidea), also called pillbugs or "roly-polies". However, millipedes and woodlice are not closely related ; rather, this is a case of convergent evolution.
Spirobolida is an order of "round-backed" millipedes containing approximately 500 species in 12 families. Its members are distinguished by the presence of a "pronounced suture that runs "vertically down the front of the head". Most of the species live in the tropics, and many are brightly coloured. Mature males have two pairs of modified legs, the gonopods, consisting of the 8th and 9th leg pair: the posterior gonopods are used in sperm-transfer while the anterior gonopods are fused into a single plate-like structure.
Glomerida is an order of pill-millipedes found primarily in the Northern Hemisphere. Also known as northern pill millipedes, they superficially resemble pill-bugs or woodlice, and can enroll into a protective ball. They have twelve body segments, 17 to 19 pairs of legs, and males have enlarged rear legs involved in mating. The order includes about 30 genera and at least 280 species, including Glomeris marginata, the common European pill-millipede. The order contains members in Europe, South-east Asia and the Americas from California to Guatemala. Although historically considered closely related with the similar sphaerotheriidans that also enroll, some DNA evidence suggest they may be more closely related to glomeridesmidans, a poorly known order that does not enroll.
Spirostreptida is an order of long, cylindrical millipedes. There are approximately 1000 described species, making Spirostreptida the third largest order of millipedes after Polydesmida and Chordeumatida.
Polydesmida is the largest order of millipedes, with more than 5,000 species, including all the millipedes reported to produce hydrogen cyanide (HCN). This order is also the most diverse of the millipede orders in terms of morphology. Millipedes in this order are found in all regions of the world other than Antarctica.
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.
Platydesmida is an order of millipedes containing two families and over 60 species. Some species practice paternal care, in which males guard the eggs.
Siphonophorida is an order of millipedes containing two families and over 100 species.
Callipodida is an order of millipedes containing around 130 species, many characterized by crests or ridges.
Pentazonia is a taxonomic infraclass of millipedes containing the pill-millipedes (Oniscomorpha) which can roll into a ball and the order Glomeridesmida which cannot. Defining traits (apomorphies) include divided sternites, a labrum with single median tooth, and an enlarged pygidium on the hind-most body segment. Pentazonia is in the dominant millipede subclass Chilognatha which have a calcified exoskeleton and modified sperm-transferring legs in males. In contrast to the Helminthomorpha – the other Chilognathan infraclass, the sperm-transferring legs are located on posterior body segments and known as telopods. Pentazonians are relatively short-bodied, with between 13 and 21 body segments. The Pentazonia contains one extinct order, Amynilyspedida, often referred to the Oniscomorpha.
Colobognatha is a clade of helminthomorph millipedes containing four orders: Platydesmida, Polyzoniida, Siphonocryptida, and Siphonophorida.
Chordeumatida is a large order of millipedes containing more than 1,400 species. Also known as sausage millipedes, they are found nearly worldwide. Chordeumatida is the largest order in the superorder Nematophora, a group also known as spinning millipedes because their telsons feature spinnerets used to build nests of silk. These millipedes produce this silk to create chambers in which to molt or to lay their eggs.
Stemmiulida is an order of millipedes consisting of approximately 130 species, reaching up to 50 mm in length. It contains a single family, Stemmiulidae.
Hirudisomatidae is a family of colobognathan millipedes in the order Polyzoniida. The approximately 20 species occur from Spain to the Himalayas in Eurasia, Japan, and in North America from southwest Canada to central Mexico.
Juliformia is a taxonomic superorder of millipedes containing three living orders: Julida, Spirobolida, and Spirostreptida, and the extinct group Xyloiuloidea known only from fossils.
Gomphodesmidae is a family of millipedes in the order Polydesmida, containing around 55 genera and 150 species. The family is native to Africa, and occurs primarily in savanna habitat from South Africa north to Senegal and Ethiopia.
Pyrgodesmidae is a family of flat-backed millipedes in the order Polydesmida. The family contains over 200 species distributed in tropics around the world. Some species are found only in ant colonies, and are considered obligate myrmecophiles.
Polyzoniidae is a family of millipedes in the order Polyzoniida. There are about 9 genera and at least 60 described species in Polyzoniidae.
Octoglena bivirgata is a species of millipede in the family Hirudisomatidae. It is found in North America.
