Pill millipedes are any members of two living (and one extinct)

orders Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...

millipede 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 resu ...

s, often grouped together into a single

superorder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

, Oniscomorpha. The name Oniscomorpha refers to the millipedes' resemblance to certain

woodlice A woodlouse (plural woodlice) is an isopod crustacean from the polyphyleticThe current consensus is that Oniscidea is actually triphyletic suborder Oniscidea within the order Isopoda. They get their name from often being found in old wood ...

(Oniscidea), also called pillbugs or "roly-polies". However, millipedes and woodlice are not closely related (belonging to the subphyla

Myriapoda 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. The fossil record of myriapods reaches back into the late Silurian ...

and

Crustacea Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group c ...

, respectively); rather, this is a case of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

Description

Pill millipedes are relatively short-bodied compared to most other millipedes, with only eleven to thirteen body segments, and are capable of rolling into a ball ( volvation) when disturbed, as a defense against predators. This ability

evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variati ...

separately in each of the two orders, making it a case of

, rather than homology. They can also exude a noxious liquid, which may be both

caustic Caustic most commonly refers to: * Causticity, a property of various corrosive substances ** Sodium hydroxide, sometimes called ''caustic soda'' ** Potassium hydroxide, sometimes called ''caustic potash'' ** Calcium oxide, sometimes called ''caust ...

and

toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a sub ...

, to repel predators. Pill millipedes are detritivorous, feeding on decomposing plant matter, usually in

woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the '' plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunlight and limited shade (see ...

Orders

Glomerida

The order Glomerida is predominantly found in the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

and includes species such as ''

Glomeris marginata ''Glomeris marginata'' is a common European species of pill millipede. It is a short millipede, rounded in cross-section, which is capable of rolling itself up into a ball ("volvation") when disturbed. This behaviour is also found in the pill wo ...

'', the common European pill millipede. They have from eleven to twelve body segments, and possess dorsal ozopores (openings of the repugnatorial glands) rather than the lateral ozopores found on many other millipedes. Glomeridans reach maximum lengths of , and eyes, if present, are in a single row of ocelli. The order contains approximately 450 species found in Europe, South-east Asia and the

Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North America, North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. ...

from

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

Guatemala Guatemala ( ; ), officially the Republic of Guatemala ( es, República de Guatemala, links=no), is a country in Central America. It is bordered to the north and west by Mexico; to the northeast by Belize and the Caribbean; to the east by Hon ...

. Four species are present in the

British Isles The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isl ...

Sphaerotheriida

The order

Sphaerotheriida Sphaerotheriida is an order of millipedes in the infraclass Pentazonia, sometimes known as giant pill millipedes. They inhabit Southern Africa, Madagascar, South and Southeast Asia, Australia and New Zealand. Like the Northern Hemisphere pill mi ...

is a

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final sta ...

-distribution taxon, with around 350 species in

southern Africa Southern Africa is the southernmost subregion of the African continent, south of the Congo and Tanzania. The physical location is the large part of Africa to the south of the extensive Congo River basin. Southern Africa is home to a number o ...

Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Afric ...

Australasia Australasia is a region that comprises Australia, New Zealand and some neighbouring islands in the Pacific Ocean. The term is used in a number of different contexts, including geopolitically, physiogeographically, philologically, and ecologic ...

and

South East Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainland ...

. Five species, all in the genus '' Procyliosoma'' are present in

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...

, and around thirty species are present in

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

. Sphaerotheriidans have thirteen body segments, and do not possess repugnatorial glands. Spherotheriidans reach larger size than Glomeridans (up to ), and always possess large, kidney-shaped eyes.

Amynilyspedida

Oniscomorpha also includes the extinct order Amynilyspedida from the upper Carboniferous of North America and Europe.Hoffman, R. L. 1969. Myriapoda, exclusive of Insecta. In ''

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology'' (or ''TIP'') published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and ...

, Pt. R, Arthropoda'' 4, ed. RC Moore, 2:R572–606. Geological Society of America, Inc., and The University of Kansas. Amynilyspedida differs from the other Oniscomorph orders in having 14–15 segments. The order contains the genus '' Amynilyspes'' with unique spines on the tergites, as well as '' Glomeropsis'', '' Archiscudderia'', and '' Palaeosphaeridium''.

References

External links

* {{Taxonbar, from=Q15981124 Millipede taxonomy