Editing Millipede (section)

==Characteristics==
[[File:Millipede body types 1.jpg|thumb|200px|alt=Representative body types|Representative body types of the Penicillata (top), Pentazonia (middle), and Helminthomorpha (bottom)]]
[[File:Millipede anterior anatomy.png|thumb|250px|alt=Body plan|Anterior anatomy of a generalized helminthomorph millipede]]
Millipedes come in a variety of body shapes and sizes, ranging from {{convert|2|mm|in|frac=16|abbr=on}} to around {{convert|35|cm|in|frac=2|abbr=on}} in length,<ref name=MyrEncylopedia>{{cite book |last1=Minelli |first1=Alessandro |last2=Golovatch |first2=Sergei I. |editor-last=Levin |editor-first=Simon A. |title=Encyclopedia of Biodiversity |year=2001 |isbn=978-0-12-226865-6 |pages=291–303 |chapter-url=http://enviro.doe.gov.my/lib/digital/1385476273-3-s2.0-B0122268652002042-main.pdf |chapter=Myriapods |publisher=Academic Press |url-status=dead |archive-url=https://web.archive.org/web/20140221184104/http://enviro.doe.gov.my/lib/digital/1385476273-3-s2.0-B0122268652002042-main.pdf |archive-date=2014-02-21 }}</ref> and can have as few as eleven to over three hundred segments.<ref name=IZ/><ref>{{Cite journal|last1=Marek|first1=Paul E.|last2=Buzatto|first2=Bruno A.|last3=Shear|first3=William A.|last4=Means|first4=Jackson C.|last5=Black|first5=Dennis G.|last6=Harvey|first6=Mark S.|last7=Rodriguez|first7=Juanita|date=2021-12-16|title=The first true millipede—1306 legs long|journal=Scientific Reports|language=en|volume=11|issue=1|pages=23126|doi=10.1038/s41598-021-02447-0|pmid=34916527|pmc=8677783|bibcode=2021NatSR..1123126M |issn=2045-2322}}</ref> They are generally black or brown in colour, although there are a few brightly coloured species, and some have [[Aposematism|aposematic]] colouring to warn that they are toxic.<ref name=Ruppert>{{cite book |title=Invertebrate Zoology, 7th edition |last1=Ruppert |first1=Edward E. |last2=Fox |first2=Richard, S. |last3=Barnes |first3=Robert D. |year=2004 |publisher=Cengage Learning |isbn=978-81-315-0104-7 |pages=711–717 }}</ref> Species of ''[[Motyxia]]'' produce [[cyanide]] as a chemical defence and are [[Bioluminescence|bioluminescent]].<ref>{{cite journal|last1=Marek|first1=Paul E.|last2=Moore|first2=Wendy|title=Discovery of a glowing millipede in California and the gradual evolution of bioluminescence in Diplopoda|journal=Proceedings of the National Academy of Sciences|date=2015|volume=112|issue=20|pages=6419–6424|doi=10.1073/pnas.1500014112|bibcode=2015PNAS..112.6419M|pmid=25941389|pmc=4443369|doi-access=free}}</ref>

Body styles vary greatly between major millipede groups. In the [[basal (evolution)|basal]] subclass [[Penicillata]], consisting of the tiny [[bristle millipede]]s, the exoskeleton is soft and uncalcified, and is covered in prominent [[seta]]e or bristles. All other millipedes, belonging to the subclass Chilognatha, have a hardened exoskeleton. The chilognaths are in turn divided into two infraclasses: the [[Pentazonia]], containing relatively short-bodied groups such as [[pill millipede]]s, and the Helminthomorpha ("worm-like" millipedes), which contains the vast majority of species, with long, many-segmented bodies.<ref name="core.ecu.edu"/><ref name="Shelley"/>

They have also lost the gene that codes for the [[Juvenile hormone acid O-methyltransferase|JHAMTl]] enzyme, which is responsible for catalysing the last step of the production of a juvenile hormone that regulates the development and reproduction in other arthropods like crustaceans, centipedes and insects.<ref>{{cite journal | doi=10.1038/s41467-022-30690-0 | title=Myriapod genomes reveal ancestral horizontal gene transfer and hormonal gene loss in millipedes | year=2022 | last1=So | first1=Wai Lok | last2=Nong | first2=Wenyan | last3=Xie | first3=Yichun | last4=Baril | first4=Tobias | last5=Ma | first5=Hai-yao | last6=Qu | first6=Zhe | last7=Haimovitz | first7=Jasmine | last8=Swale | first8=Thomas | last9=Gaitan-Espitia | first9=Juan Diego | last10=Lau | first10=Kwok Fai | last11=Tobe | first11=Stephen S. | last12=Bendena | first12=William G. | last13=Kai | first13=Zhen-Peng | last14=Hayward | first14=Alexander | last15=Hui | first15=Jerome H. L. | journal=Nature Communications | volume=13 | issue=1 | page=3010 | pmid=35637228 | pmc=9151784 | bibcode=2022NatCo..13.3010S }}</ref>
===Head===
The head of a millipede is typically rounded above and flattened below and bears a pair of large [[mandible (arthropod)|mandibles]] in front of a plate-like structure called a [[gnathochilarium]] ("jaw lip").<ref name=SierwaldBond2007/> The head contains a single pair of [[Antenna (biology)|antennae]] with seven or eight segments and a group of sensory cones at the tip.<ref name=SierwaldBond2007 /> Many orders also possess a pair of sensory organs known as the [[Organ of Tömösváry|Tömösváry organs]], shaped as small oval rings posterior and lateral to the base of the antennae. Their function is unknown,<ref name=SierwaldBond2007 /> but they also occur in some [[centipede]]s, and are possibly used to measure humidity or light levels in the surrounding environment.<ref name="Biology of Centipedes">{{cite book|last=Lewis|first=J. G. E.|title=The Biology of Centipedes|year=2008|publisher=[[Cambridge University Press]]|location=Cambridge|isbn=978-0-521-03411-1|pages=110–111|edition=Digitally printed 1st paperback version.}}</ref>

Millipede eyes consist of several simple flat-lensed [[Simple eye in invertebrates#Simple eyes in arthropods|ocelli]] arranged in a group or patch on each side of the head. These patches are also called ocular fields or ocellaria. Many species of millipedes, including the entire orders [[Polydesmida]], [[Siphoniulus|Siphoniulida]], [[Glomeridesmida]], [[Siphonophorida]] and [[Platydesmida]], and cave-dwelling millipedes such as ''[[Causeyella]]'' and ''[[Trichopetalum whitei|Trichopetalum]]'', had ancestors that could see but have subsequently lost their eyes and are blind.<ref name=MyrEncylopedia/>

===Body===
{{anchor|Diplosegment}}
[[File:Paranota comparison.png|thumb|200px|right|alt=Segmentation and paranota|Paranota of [[polydesmida]]n (left) and [[platydesmida]]n millipedes]]
Millipede bodies may be flattened or cylindrical, and are composed of numerous [[Metamerism (biology)|metameric segments]], each with an [[exoskeleton]] consisting of four [[chitin]]ous plates: a single plate above (the [[tergite]]), one at each side ([[pleurite]]s), and a plate on the underside ([[sternite]]) where the legs attach. In many millipedes, such as Merocheta and Juliformia, these plates are fused to varying degrees, sometimes forming a single cylindrical ring. The plates are typically hard, impregnated with calcium salts.<ref name=IZ>{{cite book |last=Barnes |first=Robert D. |year=1982 |title=Invertebrate Zoology |publisher=Holt-Saunders International |location=Philadelphia, PA |pages=818–825 |isbn=978-0-03-056747-6}}</ref> Because they can't close their permanently open spiracles and most species lack a waxy cuticle, millipedes are susceptible to water loss and with a few exceptions must spend most of their time in moist or humid environments.<ref>{{cite book |editor-last=Capinera |editor-first=John L. |year=2008 |title=Encyclopedia of Entomology |publisher=[[Springer Science+Business Media|Springer]] |isbn=978-1-4020-6242-1 |chapter-url=https://books.google.com/books?id=i9ITMiiohVQC&pg=PA2396 |chapter=Millipedes |pages=2395–2397 |access-date=2015-10-27 |archive-date=2016-05-15 |archive-url=https://web.archive.org/web/20160515092050/https://books.google.com/books?id=i9ITMiiohVQC&pg=PA2396 |url-status=live }}</ref>

The first segment behind the head is legless and known as a collum (from the Latin for neck or collar). The second, third, and fourth body segments bear a single pair of legs each and are known as "haplosegments" (the three haplosegments are sometimes referred to as a "[[Thorax#In arthropods|thorax]]"<ref name="Wilson&Anderson2004"/>). The remaining segments, from the fifth to the posterior, are properly known as diplosegments or double segments, formed by the fusion of two embryonic segments. Each diplosegment bears two pairs of legs, rather than just one as in centipedes. In some millipedes, the last few segments may be legless. The terms "segment" or "body ring" are often used interchangeably to refer to both haplo- and diplosegments. The final segment is known as the [[telson]] and consists of a legless preanal ring, a pair of anal valves (closeable plates around the anus), and a small scale below the anus.<ref name=SierwaldBond2007/><ref name=IZ/>

Millipedes in several orders have keel-like extensions of the body-wall known as [[paranota]], which can vary widely in shape, size, and texture; modifications include lobes, papillae, ridges, crests, spines and notches.<ref name=Ruppert/> Paranota may allow millipedes to wedge more securely into crevices, protect the legs, or make the millipede more difficult for predators to swallow.<ref name=PolyParanota>{{cite web |last=Mesibov |first=Robert|authorlink=Robert Mesibov |title=Paranota |work=External Anatomy of Polydesmida |url=http://www.polydesmida.info/polydesmida/paranota.html |access-date=30 October 2013 |archive-url=https://web.archive.org/web/20160304074552/http://www.polydesmida.info/polydesmida/paranota.html |archive-date=4 March 2016 |url-status=dead }}</ref>

The legs are composed of seven segments, and attach on the underside of the body. The legs of an individual are generally rather similar to each other, although often longer in males than females, and males of some species may have a reduced or enlarged first pair of legs.<ref name=Hopkin&Read/> The most conspicuous leg modifications are involved in reproduction, discussed below. Despite the common name, no millipede was known to have 1,000 legs until 2021: common species have between 34 and 400 legs, and the record is held by ''[[Eumillipes persephone]]'', with individuals possessing up to 1,306 legs – more than any other creature on Earth.<ref name=Marek-etal-2021-Eumillipes>{{cite journal |last1=Marek |first1=Paul E. |last2=Buzatto |first2=Bruno A. |last3=Shear |first3=William A. |last4=Means |first4=Jackson C. |last5=Black |first5=Dennis G. |last6=Harvey |first6=Mark S. |last7=Rodriguez |first7=Juanita |title=The first true millipede—1306 legs long |journal=[[Scientific Reports]] |date=2021 |volume=11 |issue=1 |pages=23126 |doi=10.1038/s41598-021-02447-0|pmid=34916527 |pmc=8677783 |bibcode=2021NatSR..1123126M }}</ref><ref>{{cite news |last1=Lu |first1=Donna |title=The first true millipede: new species with more than 1,000 legs discovered in Western Australia |url=https://www.theguardian.com/world/2021/dec/16/the-first-true-millipede-new-species-with-more-than-1000-legs-discovered-in-western-australia |work=The Guardian |date=16 December 2021 |language=en |access-date=16 December 2021 |archive-date=16 December 2021 |archive-url=https://web.archive.org/web/20211216180701/https://www.theguardian.com/world/2021/dec/16/the-first-true-millipede-new-species-with-more-than-1000-legs-discovered-in-western-australia |url-status=live }}</ref><ref name=Marek>{{Cite journal | last1 = Marek | first1 = P. | last2 = Shear | first2 = W. | last3 = Bond | first3 = J. | title = A redescription of the leggiest animal, the millipede ''Illacme plenipes'', with notes on its natural history and biogeography (Diplopoda, Siphonophorida, Siphonorhinidae) | doi = 10.3897/zookeys.241.3831 | journal = ZooKeys | pages = 77–112 | year = 2012 | pmid =  23372415| pmc =3559107 | issue = 241 | doi-access = free | bibcode = 2012ZooK..241...77M }}</ref>
[[File:Female Illacme plenipes (MIL0020) with 618 legs - ZooKeys-241-077-SP-6-top.jpg|thumb|center|600px|alt=Millipede with 618 legs|A female ''[[Illacme plenipes]]'' with 618 legs (309 pairs)]]

===Internal organs===
Millipedes breathe through two pairs of spiracles located ventrally on each segment near the base of the legs.<ref name="Shelley 1999"/> Each opens into an internal pouch, and connects to a system of [[Invertebrate trachea|tracheae]]. The heart runs the entire length of the body, with an [[aorta]] stretching into the head. The excretory organs are two pairs of [[malpighian tubule]]s, located near the mid-part of the gut. The digestive tract is a simple tube with two pairs of [[salivary gland]]s to help digest the food.<ref name=IZ/>