Editing Isopoda (section)

==Description==
[[File:Porcellio scaber - male side 2 (aka).jpg|thumb|left|The [[woodlouse]] ''[[Oniscus asellus]]'' showing the head with eyes and antennae, carapace and relatively uniform limbs]]
[[File:Hypsimetopidae, Marrawah TAS 7330, Australia imported from iNaturalist photo 106796687.jpg|thumb|A [[Phreatoicidea|phreatoicidean]] isopod, in Australia]]
Classified within the [[arthropod]]s, isopods have a [[chitin]]ous exoskeleton and jointed limbs.<ref>{{cite book |first=J. W. |last=Valentine |author-link=James W. Valentine |title=On the Origin of Phyla |publisher=[[University of Chicago Press]] |year=2004 |isbn=978-0-226-84548-7 |page=33 |url=https://books.google.com/books?id=DMBkmHm5fe4C&q=arthropod+synapomorphy}}</ref> Isopods are typically flattened [[dorsoventral]]ly (broader than they are deep),<ref name="Academic Press">{{cite book |last1=Naylor |first1=E. |title=British Marine Isopods: Keys and Notes for the Identification of the Species |year=1978 |publisher=Academic Press |isbn=978-0-12-515150-4 |page=[https://archive.org/details/britishmarineiso0000nayl/page/2 2] |edition=2nd |url=https://archive.org/details/britishmarineiso0000nayl/page/2 }}</ref> although many species deviate from this rule, particularly parasitic forms, and those living in the deep sea or in [[groundwater|ground water habitats]]. Their colour may vary, from grey to white,<ref>{{cite web |title=Isopod, Pillbug, Sow Bug Information |url=http://insected.arizona.edu/isoinfo.htm |year=1997 |publisher=University of Arizona |access-date=21 August 2014 |url-status=dead |archive-url=https://web.archive.org/web/20140923101009/http://insected.arizona.edu/isoinfo.htm |archive-date=23 September 2014 |df=dmy-all }}</ref> or in some cases red, green, or brown.<ref>{{cite journal |last1=Lee |first1=Welton L. |title=Color change and the ecology of the marine isopod ''Idothea (Pentidotea) montereyensis'' Maloney, 1933 |journal=[[Ecology (journal)|Ecology]] |year=1966 |volume=47 |issue=6 |jstor=1935640 |pages=930–941 |doi=10.2307/1935640|bibcode=1966Ecol...47..930L }}</ref> Isopods vary in size, ranging from some [[Microcerberidae]] species of just {{convert|.3|mm|3}} to the deep sea [[giant isopod]] ''Bathynomus'' [[Species#Abbreviations|spp.]] of nearly {{convert|50|cm|0|abbr=on}}.<ref name="Marine"/> Giant isopods lack an obvious [[carapace]] (shell), which is reduced to a "cephalic shield" covering only the head. This means that the [[Gill#Invertebrate gills|gill]]-like structures, which in other related groups are protected by the carapace, are instead found on specialised limbs on the abdomen.<ref name="Marine"/><ref name="AM">{{cite web |url=http://www.crustacea.net/crustace/isopoda/index.htm |title=Australian Isopoda: Families |last1=Keable |first1=S. J. |last2=Poore |first2=G. C. B. |last3=Wilson |first3=G. D. F. |publisher=[[Australian Museum]] |date=2 October 2002 |access-date=5 June 2014 |archive-url=https://web.archive.org/web/20181010185506/http://www.crustacea.net/crustace/isopoda/index.htm |archive-date=10 October 2018 |url-status=dead }}</ref> The [[Dorsum (anatomy)|dorsal]] (upper) surface of the animal is covered by a series of overlapping, articulated plates which give protection while also providing flexibility. The isopod body plan consists of a head (cephalon), a thorax (pereon) with seven segments (pereonites), and an abdomen (pleon) with six segments (pleonites), some of which may be fused.<ref name="Academic Press"/> The head is fused with the first segment of the thorax to form the [[Cephalon (arthropod head)|cephalon]]. There are two pairs of unbranched [[Antenna (biology)|antennae]], the first pair being [[Vestigiality|vestigial]] in land-dwelling species. The eyes are [[Eye#Compound eyes|compound]] and unstalked and the mouthparts include a pair of [[maxilliped]]s and a pair of [[Mandible (arthropod mouthpart)|mandibles]] (jaws) with palps (segmented appendages with sensory functions) and lacinia mobilis (spine-like movable appendages).<ref name=Ruppert>{{cite book |last1=Ruppert |first1=Edward E. |last2=Barnes |first2=Richard S. |last3=Fox |first3=Robert D. |year=2004 |title=Invertebrate Zoology |edition=7th |location=Delhi |publisher=Cengage Learning |pages=661–667 |isbn=978-81-315-0104-7 |oclc=970002268}}</ref>

The seven free segments of the thorax each bear a pair of unbranched pereopods (limbs). In most species these are used for locomotion and are of much the same size, [[morphology (biology)|morphology]] and orientation, giving the order its name "Isopoda", from the [[Greek language|Greek]] ''equal foot''. In a few species, the front pair are modified into [[gnathopod]]s with clawed, gripping terminal segments. The pereopods are not used in respiration, as are the equivalent limbs in [[amphipod]]s, but the coxae (first segments) are fused to the [[Tergum|tergites]] (dorsal plates) to form epimera (side plates). In mature females, some or all of the limbs have appendages known as [[oostegite]]s which fold underneath the thorax and form a [[Brood pouch (Peracarida)|brood chamber]] for the eggs. In males, the [[gonopore]]s (genital openings) are on the ventral surface of segment eight and in the females, they are in a similar position on segment six.<ref name=Ruppert/>

One or more of the abdominal segments, starting with the sixth segment, is fused to the [[telson]] (terminal section) to form a rigid [[pleotelson]].<ref name=Ruppert/><ref>{{cite journal|last1=Wilson|first1=G. D. F.|title=A systematic revision of the deep-sea subfamily Lipomerinae of the isopod crustacean family Munnopsidae |journal=Bulletin of the Scripps Institution of Oceanography |year=1989 |volume=27 |pages=1–138 |url=https://escholarship.org/uc/item/5nm8z7td}}</ref><ref>{{cite journal |last1=Wilson |first1=G. D. F. |title=The road to the Janiroidea: Comparative morphology and evolution of the asellote isopod crustaceans |journal=[[Journal of Zoological Systematics and Evolutionary Research]] |year=2009 |volume=25 |issue=4 |pages=257–280 |doi=10.1111/j.1439-0469.1987.tb00608.x|doi-access=free }}</ref> The first five abdominal segments each bear a pair of [[biramous]] (branching in two) pleopods ([[Lamella (anatomy)|lamellar]] structures which serve the function of gas exchange, and in aquatic species serve as [[gills]] and propulsion),<ref name="Marine"/><ref>{{cite book |last1=Wilson |first1=George D.&nbsp;F. |editor-last=Bauer |editor-first= Raymond T. |editor2-last=Martin |editor2-first=Joel W. |title=Crustacean Sexual Biology |publisher=Columbia University Press |year=1991 |pages=228–245 |chapter=Functional morphology and evolution of isopod genitalia |isbn=978-0-231-06880-2 }}</ref> and the last segment bears a pair of biramous [[uropod]]s (posterior limbs). In males, the second pair of pleopods, and sometimes also the first, are modified for use in transferring [[sperm]]. The endopods (inner branches of the pleopods) are modified into structures with thin, permeable cuticles (flexible outer coverings) which act as gills for [[gas exchange]].<ref name=Ruppert/> In some terrestrial isopods, these resemble [[lung]]s.<ref name="Marine"/>