Editing Amphipoda (section)

==Description==

===Anatomy===
[[File:Scheme amphipod anatomy-en.svg|thumb|left|Diagram of the anatomy of the [[gammaridea]]n amphipod ''[[Leucothoe incisa]]'']]
The body of an amphipod is divided into 13 segments, which can be [[tagmosis|grouped into]] a head, a [[thorax]] and an abdomen.<ref name="Wade">{{cite book |first1=Sam |last1=Wade |first2=Tracy |last2=Corbin |first3=Linda-Marie |last3=McDowell |isbn=1-876562-67-6 |year=2004 |publisher=Waterwatch South Australia |title=Critter Catalogue. A guide to the aquatic invertebrates of South Australian inland waters |chapter=Class Crustacea |url=http://www.sa.waterwatch.org.au/pdfs/critters_5_crustaceans.pdf  |archive-url=https://web.archive.org/web/20091017035859/http://sa.waterwatch.org.au/pdfs/critters_5_crustaceans.pdf |archive-date=2009-10-17 }}</ref>

The head is fused to the thorax, and bears two pairs of [[antenna (biology)|antennae]] and one pair of sessile [[compound eye]]s.<ref name="TAFI">{{cite web|url=http://www.tafi.org.au/zooplankton/imagekey/malacostraca/peracarida/amphipoda/amphipoda.html |title=Order Amphipoda |work=Guide to the marine zooplankton of south eastern Australia |year=2008 |publisher=[[Tasmanian Aquaculture & Fisheries Institute]]  |archive-url=https://web.archive.org/web/20080720143838/http://www.tafi.org.au/zooplankton/imagekey/malacostraca/peracarida/amphipoda/amphipoda.html |archive-date=2008-07-20 }}</ref> It also carries the [[arthropod mouthparts|mouthparts]], but these are mostly concealed.<ref name="Holsinger"/>

The thorax and abdomen are usually quite distinct and bear different kinds of legs; they are typically laterally compressed, and there is no [[carapace]].<ref name="TAFI"/> The thorax bears eight pairs of [[uniramous]] [[appendage]]s, the first of which are used as accessory [[arthropod mouthparts|mouthparts]]; the next four pairs are directed forwards, and the last three pairs are directed backwards.<ref name="TAFI"/> Gills are present on the thoracic segments, and there is an [[open circulatory system]] with a [[heart]], using [[Hemocyanin|haemocyanin]] to carry [[oxygen]] in the [[hemolymph|haemolymph]] to the tissues. The uptake and [[excretion]] of [[salt (chemistry)|salts]] is controlled by special [[gland]]s on the antennae.<ref name="Wade"/>

The abdomen is divided into two parts: the pleosome which bears [[pleopod|swimming legs]]; and the urosome, which comprises a [[telson]] and three pairs of [[uropod]]s which do not form a tail fan as they do in animals such as [[true shrimp]].<ref name="TAFI"/>

===Size===
[[File:Amphipodredkils (flipped).jpg|thumb|right|Amphipods are typically less than {{convert|10|mm|1}} long.]]
[[File:Lepidepecreum longicornis.jpg|thumb|''[[Lepidepecreum longicorne]]'' ([[Amphilochidea]]: [[Lysianassidae]])]]
[[File:Pariambus typicus.jpg|thumb|''[[Pariambus typicus]]'' ([[Senticaudata]]: [[Caprellidae]])]]
[[File:Hyperia galba.jpg|thumb|''[[Hyperia galba]]'' ([[Hyperiidea]]: [[Hyperiidae]])]]

Amphipods are typically less than {{convert|10|mm|1}} long, but the largest recorded living amphipods were {{convert|28|cm}} long, and were photographed at a depth of {{convert|5300|m}} in the [[Pacific Ocean]].<ref name="Morris">{{cite book |first1=J. Laurens |last1=Barnard |first2=Darl E. |last2=Bowers |first3=Eugene C. |last3=Haderlie |chapter=Amphipoda: The Amphipods and Allies |title=Intertidal Invertebrates of California |editor1-first = Robert H. | editor1-last = Morris | editor2-first = Robert Hugh | editor2-last = Morris | editor3-first = Donald Putnam | editor3-last = Abbott | editor4-first = Eugene Clinton | editor4-last = Haderlie  |pages=559–566 |year=1980 |publisher=[[Stanford University Press]] |isbn=0-8047-1045-7}}</ref> Samples retrieved from the stomach of a [[black-footed albatross]] had a reconstructed length of {{convert|34|cm}}; it was assigned to the same species, ''[[Alicella gigantea]]''.<ref>{{cite journal |doi=10.2307/1548395 |title=The supergiant amphipod ''Alicella gigantea'' Chevreux from the North Pacific Gyre |first1=J. Laurens |last1=Barnard |first2=Camilla L. |last2=Ingram |journal=[[Journal of Crustacean Biology]] |volume=6 |issue=4 |year=1986 |pages=825–839 |jstor=1548395}}</ref> A study of the [[Kermadec Trench]] observed more specimens of ''A. gigantea'', the largest of which was estimated at 34.9&nbsp;cm long, and collected some for examination, the largest of which was measured at 27.8&nbsp;cm long.<ref>{{Cite journal |last1=Jamieson |first1=A. J. |last2=Lacey |first2=N. C. |last3=Lörz |first3=A. -N. |last4=Rowden |first4=A. A. |last5=Piertney |first5=S. B. |date=2013-08-01 |title=The supergiant amphipod Alicella gigantea (Crustacea: Alicellidae) from hadal depths in the Kermadec Trench, SW Pacific Ocean |url=https://www.sciencedirect.com/science/article/pii/S0967064512001932 |journal=Deep Sea Research Part II: Topical Studies in Oceanography |series=Deep-Sea Biodiversity and Life History Processes |language=en |volume=92 |pages=107–113 |doi=10.1016/j.dsr2.2012.12.002 |bibcode=2013DSRII..92..107J |issn=0967-0645|url-access=subscription }}</ref> The smallest known amphipods are less than {{convert|1|mm|2}} long.<ref>{{cite journal |doi=10.1098/rstb.1969.0014 |title=The fauna of Rennell and Bellona, Solomon Islands |first=T. |last=Wolff |journal=Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences |volume=255 |issue=800 |year=1969 |pages=321–343 |jstor=2416857|bibcode=1969RSPTB.255..321W |doi-access= }}</ref> The size of amphipods is limited by the availability of [[dissolved oxygen]], such that the amphipods in [[Lake Titicaca]] at an altitude of {{convert|3800|m}} can only grow up to {{convert|22|mm}}, compared to lengths of {{convert|90|mm}} in [[Lake Baikal]] at {{convert|455|m|-2}}.<ref>{{cite journal |first1=L.&nbsp;S. |last1=Peck |first2=G. |last2=Chapelle |title=Reduced oxygen at high altitude limits maximum size |doi=10.1098/rsbl.2003.0054 |journal=[[Proceedings of the Royal Society B]] |year=2003 |volume=270 |issue=Suppl 2 |pages=S166–S167 |pmid=14667371 |pmc=1809933}}</ref>

Some amphipods exhibit [[sexual dimorphism]]. In dimorphic species, males are usually larger than females, although this is reversed in the genus [[Crangonyx]].<ref name=Glazier/>

===Reproduction and life cycle===
Amphipods engage in [[amplexus]], a precopulatory guarding behavior in which males will grasp a female with their gnathopods (enlarged appendages used for feeding) and carry the female held against their ventral surface. Amplexus can last from two to over fifteen days, depending on water temperature, and ends when the female molts, at which point her eggs are ready for fertilisation.<ref name=Glazier>{{cite encyclopedia |last=Glazier |first=Doug |editor-last= Likens |editor-first=Gene |encyclopedia=Encyclopedia of Inland Waters |title=Amphipoda |year=2009 |publisher=Academic Press |isbn=978-0-12-088462-9 |doi=10.1016/B978-012370626-3.00154-X |pages=89–115 }}</ref>

Mature females bear a ''marsupium'', or [[brood pouch (Peracarida)|brood pouch]], which holds her [[egg (biology)|eggs]] while they are [[fertilisation|fertilised]],<ref name="Wade"/> and until the young are ready to hatch.<ref name="TAFI"/> As a female ages, she produces more eggs in each brood. Mortality is around 25–50% for the eggs.<ref name="Wade"/> There are no [[larva]]l stages; the eggs hatch directly into a [[Juvenile (organism)|juvenile]] form, and [[sexual maturity]] is generally reached after 6 [[ecdysis|moults]].<ref name="Wade"/> Some species have been known to eat their own [[exuvia]]e after moulting<ref name="Wade"/>