| Pill millipedes | |
|---|---|
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| AnArthrosphaera fumosagiant pill millipede from India. | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Myriapoda |
| Class: | Diplopoda |
| Subclass: | Chilognatha |
| Infraclass: | Pentazonia |
| Superorder: | Oniscomorpha Pocock, 1887 [1] |
| Orders | |
| Synonyms | |
ArmadillomorphaVerhoeff, 1915 | |
Pill millipedes are any members of two living (and one extinct)orders ofmillipedes, often grouped together into a singlesuperorder,Oniscomorpha. The name Oniscomorpha refers to the millipedes' resemblance to certainwoodlice (Oniscidea), also called pillbugs or "roly-polies". However, millipedes and woodlice are not closely related (belonging to thesubphylaMyriapoda andCrustacea, respectively); rather, this is a case ofconvergent evolution.
Pill millipedes are relatively short-bodied compared to most other millipedes, with only eleven to thirteenbody segments,[2] and are capable of rolling into a ball (volvation) when disturbed, as adefense against predators. This abilityevolved separately in each of the two orders, making it a case ofconvergent evolution, rather thanhomology. They can alsoexude a noxious liquid, which may be bothcaustic andtoxic among other millipede taxa, but is not in pill millipedes——Glomerida secretes a clear, odorless liquid from the midline of the back that contains toxic alkaloids and has a sedative effect to repel predators.Sphaerotheriida don't even have such ability, they completely rely on their hard shell to defend against enemies.[3] Pill millipedes aredetritivorous, feeding on decomposing plant matter, usually inwoodlands.[4]
The orderGlomerida is predominantly found in theNorthern Hemisphere and includes species such asGlomeris marginata, the common European pill millipede. They have from eleven to twelve body segments, and possess dorsalozopores (openings of therepugnatorial glands) rather than the lateral ozopores found on many other millipedes.[3] Glomeridans reach maximum lengths of 20 mm (0.79 in), and eyes, if present, are in a single row of ocelli.[5] The order contains approximately 450 species[6] found in Europe,South-east Asia and theAmericas fromCalifornia toGuatemala.[7] Four species are present in theBritish Isles.[8]
The orderSphaerotheriida is aGondwana-distribution taxon, with around 350 species insouthern Africa,Madagascar,[9]Australasia[10] andSouth East Asia.[7] Five species, all in the genusProcyliosoma are present inNew Zealand,[10] and around thirty species are present inAustralia.[11] Sphaerotheriidans have thirteen body segments, and do not possess repugnatorial glands. Spherotheriidans reach larger size than Glomeridans (up to 10 cm (3.9 in)), and always possess large, kidney-shaped eyes.[5]
Oniscomorpha also includes the extinct orderAmynilyspedida from theupper Carboniferous of North America and Europe.[2][12] Amynilyspedida differs from the other Oniscomorph orders in having 14–15 segments.[13] The order contains the genusAmynilyspes with unique spines on thetergites, as well asGlomeropsis,Archiscudderia, andPalaeosphaeridium.[2]
Data related toOniscomorpha at WikispeciesOrders of the classDiplopoda(millipedes) | |||||||||||||||||||||||||||||||||
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