Editing Ostracod (section)

==Description==
[[File:CypridinaMediterranea.png|thumb|left|upright|Anatomy of ''[[Cypridina mediterranea]]'']]
The body of an ostracod is encased by a carapace originating from the head region, and consists of two valves superficially resembling the shell of a clam. A distinction is made between the valve (hard parts) and the body with its appendages (soft parts). Studies of the embryonic development in [[Myodocopida]] show that the bivalved carapace develops from two independent buds of the carapace valves. As the two halves grow, they meet in the middle. In ''[[Manawa (crustacean)|Manawa]]'', an ostracod in the order [[Palaeocopida]], the carapace originates as a single element and during growth folds at the midline.<ref>{{cite journal |last1=Betts |first1=Marissa J. |last2=Brock |first2=Glenn A. |last3=Paterson |first3=John R. |title=Butterflies of the Cambrian benthos? Shield position in bradoriid arthropods |journal=Lethaia |date=October 2016 |volume=49 |issue=4 |pages=478–491 |doi=10.1111/let.12160 |bibcode=2016Letha..49..478B }}</ref><ref>{{cite journal |last1=Wakayama |first1=N. |title=Embryonic development clarifies polyphyly in ostracod crustaceans |journal=Journal of Zoology |date=December 2007 |volume=273 |issue=4 |pages=406–413 |doi=10.1111/j.1469-7998.2007.00344.x }}</ref>

===Body parts===
[[File:Ostracod_swimming_motions_20200520.gif|thumb|right|upright|Ostracod swimming motions (in real time)]]
The body consists of a head and [[thorax]], separated by a slight constriction. Unlike many other crustaceans, the body is not clearly divided into [[segmentation (biology)|segments]]. Most species have completely or partly lost their trunk segmentation, and there are no boundaries between the thorax and [[Abdomen#Other animals|abdomen]], and it has therefore been impossible to tell if the first pair of limbs after the maxillae belongs to the head or the thorax. With a few exceptions, like [[Platycopida|platycopids]] which have an 11-segmented trunk, the abdomen in ostracods has no visible segments.<ref>{{cite journal |last1=Ikuta |first1=Kyosuke |title=Expression of two ''engrailed'' genes in the embryo of ''Vargula hilgendorfii'' (Müller, 1890) (Ostracoda: Myodocopida) |journal=Journal of Crustacean Biology |date=18 January 2018 |volume=38 |issue=1 |pages=23–26 |doi=10.1093/jcbiol/rux099 }}</ref>

The head is the largest part of the body, and bears four pairs of appendages. Two pairs of well-developed [[antenna (biology)|antennae]] are used to swim through the water. In addition, there are a pair of [[mandible (arthropod)|mandibles]] and a pair of [[Maxilla (arthropod mouthpart)|maxillae]]. The thorax has three primary pairs of appendages. The first of these has different functions in different groups. It can be used for feeding ([[Cypridoidea]]) or for walking ([[Cytheroidea]]), and in some species it has evolved into a male clasping organ. The second pair is mainly used for locomotion, and the third is used for walking or cleaning, but can also be reduced or absent. Both the second and third pair are absent in suborder [[Cladocopina]].<ref>{{cite journal |last1=Kornicker |first1=Louis S. |last2=Sohn |first2=I. G. |title=Phylogeny, ontogeny & morphology of living and fossil Thaumatocypridacea (Myodocopa: Ostracoda) |journal=Smithsonian Contributions to Zoology |date=1976 |issue=219 |pages=1–124 |doi=10.5479/si.00810282.219 }}</ref> In the [[Myodocopina]] the third pair is a multisegmented cleaning organ that resembles a worm. Their external genitals seem to originate from the fusion of three to five appendages. The two "rami", or projections, from the tip of the tail point downward and slightly forward from the rear of the shell.<ref name=IZ>{{cite book |author=Robert D. Barnes |year=1982 |title= Invertebrate Zoology |publisher=[[Holt-Saunders International]] |location=[[Philadelphia]] |pages=680–683 |isbn=978-0-03-056747-6}}</ref><ref>{{cite book |doi=10.1016/B978-012370626-3.00184-8 |chapter=Ostracoda |title=Encyclopedia of Inland Waters |date=2009 |last1=Martens |first1=K. |last2=Horne |first2=D.J. |pages=405–414 |isbn=978-0-12-370626-3 }}</ref><ref>{{cite book|title=Recent Freshwater Ostracods of the World: Crustacea, Ostracoda, Podocopida|last=Karanovic|first=Ivana|publisher=Springer|year=2012|isbn=978-3-642-21809-5|doi=10.1007/978-3-642-21810-1|lccn=2011944255|pages=5–47|s2cid=40120445 }} [https://books.google.com/books?id=orzLHglZlEUC&dq=%22This%20appendage%20is%20absent%20in%20the%20order%20Platycopida%20(Podocopa)%20and%20Cladocopina%20(Myodocopa).%22&pg=PA40 Limited preview via Google Books]</ref>{{rp|40}}

All ostracods have a pair of "ventilatory appendages" that beat rhythmically, which create a water current between the body and the inner surface of the carapace. [[Podocopa]], the largest subclass, have no gills, [[heart]] or circulatory system, so the gas exchange take place all over the surface. The other subclass of ostracods, the Myodocopa, do have a heart, and the family [[Cylindroleberididae]] also have 6–8 lamellar gills. Certain other larger members of Myodocopa, even if they don't have gills, have a circulatory system where hemolymph sinuses absorbs oxygen through special areas on the inner wall of the carapace.<ref>{{Cite journal |last1=Williams |first1=Mark |last2=Vannier |first2=Jean |last3=Corbari |first3=Laure |last4=Massabuau |first4=Jean-Charles |date=2011 |title=Oxygen as a driver of early arthropod micro-benthos evolution |journal=PLOS ONE |volume=6 |issue=12 |pages=e28183 |doi=10.1371/journal.pone.0028183 |doi-access=free |pmc=3229522 |pmid=22164241|bibcode=2011PLoSO...628183W }}</ref><ref>{{cite journal|title=The early life history of tissue oxygenation in crustaceans: the strategy of the myodocopid ostracod ''Cylindroleberis mariae''|last1=Corbari|first1=Laure|last2=Carbonel|first2=Pierre|last3=Massabuau|first3=Jean-Charles|journal=Journal of Experimental Biology|year=2005|volume=208|issue=4|pages=661–670|doi=10.1242/jeb.01427|pmid=15695758 |s2cid=30226212 |doi-access=|bibcode=2005JExpB.208..661C }}</ref> In addition, the respiratory protein [[hemocyanin]] has been found in the two orders Myodocopida and Platycopida.<ref>{{Cite journal |last1=Marxen |first1=Julia C. |last2=Pick |first2=Christian |last3=Oakley |first3=Todd H. |last4=Burmester |first4=Thorsten |date=August 2014 |title=Occurrence of hemocyanin in ostracod crustaceans |url=https://pubmed.ncbi.nlm.nih.gov/25135304 |journal=Journal of Molecular Evolution |volume=79 |issue=1–2 |pages=3–11 |doi=10.1007/s00239-014-9636-x |pmid=25135304|bibcode=2014JMolE..79....3M }}</ref> Nitrogenous waste is excreted through glands on the maxillae, antennae, or both.<ref name=IZ/>

The primary sense of ostracods is likely touch, as they have several sensitive hairs on their bodies and appendages. Compound eyes are only found in [[Myodocopina]] within the Myodocopa.<ref>{{cite journal|last1=Oakley|first1=Todd H.|last2=Cunningham|first2=Clifford W.|title=Molecular phylogenetic evidence for the independent evolutionary origin of an arthropod compound eye|journal=Proceedings of the National Academy of Sciences USA|volume=99|issue=3|pages=1426–1430|year=2002|pmid=11818548|pmc=122207|doi=10.1073/pnas.032483599|bibcode=2002PNAS...99.1426O |doi-access=free}}</ref> The order [[Halocyprida]] in the same subclass is eyeless.<ref>[https://www.zobodat.at/pdf/BioEco_11_0123-0143.pdf The darkness syndrome in subsurface-shallow and deep-sea dwelling Ostracoda (Crustacea)]</ref> Podocopid ostracods have just a [[naupliar eye]] consisting of two lateral ocelli and a single ventral ocellus, but the ventral one is absent in some species.<ref name=IZ/><ref>{{cite journal|title=Functional morphology and light-gathering ability of podocopid ostracod eyes and the palaeontological implications|last=Tanaka|first=Gengo|journal=Zoological Journal of the Linnean Society|volume=147|issue=1|year=2006|pages=97–108|doi=10.1111/j.1096-3642.2006.00216.x|doi-access=free}}</ref><ref>{{cite journal|title=A gigantic marine ostracod (Crustacea: Myodocopa) trapped in mid-Cretaceous Burmese amber|last1=Xing|first1=Lida|last2=Sames|first2=Benjamin|last3=McKellar|first3=Ryan C.|last4=Xi|first4=Dangpeng|last5=Bai|first5=Ming|last6=Wan|first6=Xiaoqiao|journal=Scientific Reports|year=2018|volume=8|issue=1 |page=1365 |id=1365|doi=10.1038/s41598-018-19877-y|pmid=29358761 |pmc=5778021 |bibcode=2018NatSR...8.1365X |doi-access=free}}</ref> Platycopida was assumed to be completely eyeless, but two species, ''[[Keijcyoidea infralittoralis]]'' and ''[[Cytherella sordida]]'', have been found to both possess a nauplius eye too.<ref>{{cite journal|doi=10.1144/jm.29.1.81|doi-access=free|title=Talking about a re-evolution: blind alleys in ostracod phylogeny|last=Horne|first=David J.|year=2010|journal=Journal of Micropalaeontology|volume=29|issue=1|pages=81-85}}</ref>