Editing Mysida

{{Short description|Small, shrimp-like crustacean}}
{{good article}}
{{Automatic taxobox
| name = Mysida 
| image = Hemimysis anomala GLERL 4.jpg
| image_caption = ''[[Hemimysis anomala]]'' ([[Mysidae]])
| taxon = Mysida
| authority = [[Johan Erik Vesti Boas|Boas]], 1883<ref name=WoRMS>{{cite WoRMS |author=Mees, J. |year=2013 |title=Mysida |id=149668 |access-date=2014-01-30 }}</ref> 
| subdivision_ranks =  [[Family (biology)|Families]]
| subdivision =
*[[Mysidae]]
*[[Petalophthalmidae]]
}}

'''Mysida''' is an [[order (biology)|order]] of small, [[shrimp]]-like [[crustacean]]s in the [[malacostraca]]n [[superorder]] [[Peracarida]]. Their [[common name]] '''opossum shrimps''' stems from the presence of a [[Brood pouch (Peracarida)|brood pouch]] or "marsupium" in females. The fact that the [[Crustacean larvae|larvae]] are reared in this pouch and are not [[Motility|free-swimming]] characterises the order. The mysid's head bears a pair of stalked eyes and two pairs of antennae. The thorax consists of eight segments each bearing branching limbs, the whole concealed beneath a protective [[carapace]] and the abdomen has six segments and usually further small limbs.

Mysids are found throughout the world in both shallow and deep marine waters where they can be [[Benthos|benthic]] or [[pelagic]], but they are also important in some [[fresh water]] and [[brackish water|brackish]] [[ecosystem]]s. Many benthic species make [[Diel vertical migration|daily vertical migrations]] into higher parts of the [[water column]]. Mysids are [[filter feeder]]s, [[omnivore]]s that feed on [[algae]], [[detritus]] and [[zooplankton]]. Some mysids are cultured in laboratories for experimental purposes and are used as a food source for other cultured marine organisms. They are sensitive to water [[Pollutant|pollution]], so are sometimes used as [[bioindicator]]s to monitor [[water quality]].

==Description== 
The head of a mysid bears two pairs of antennae and a pair of large, stalked eyes. The head and first segment (or sometimes the first three segments) of the thorax are fused to form the [[cephalothorax]]. The eight thoracic segments are covered by the [[carapace]] which is attached only to the first three. The first two thoracic segments bear [[maxilliped]]s which are used to filter plankton and organic particulate from the water. The other six pairs of thoracic appendages are [[biramous]] (branching) limbs known as [[pereopod]]s, and are used for swimming, as well as for wafting water towards the maxillipeds for feeding.  Unlike true shrimps ([[Caridea]]), females have a [[Brood pouch (Peracarida)|marsupium]] beneath the thorax. This brood pouch is enclosed by the large, flexible oostegites, bristly flaps which extend from the basal segments of the pereopods and which form the floor of a chamber roofed by the animal's [[Sternum (arthropod anatomy)|sternum]]. This chamber is where the eggs are brooded, [[Marine larval ecology#Larval development strategies|development being direct]] in most cases.<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=652–654 }}</ref>

The abdomen has six segments, the first five of which bear [[pleopod]]s, although these may be absent or vestigial in females. The fourth pleopod is longer than the others in males and has a specialized reproductory function.<ref name=Ruppert/>

The majority of species are {{convert|5|-|25|mm|1|abbr=on}} long, and vary in colour from pale and transparent, through to bright orange or brown. They differ from other species within the superorder [[Peracarida]] by featuring [[statocyst]]s on their [[uropod]]s (located on the last abdominal segment). These help the animal orient itself in the water and are clearly seen as circular [[Vesicle (biology)|vesicles]]: together with the pouch the statocysts are often used as features that distinguish mysids from other shrimp-like organisms.<ref name="Mauchline"/>

==Distribution==
Mysids have a [[cosmopolitan distribution]] and are found in both marine and freshwater environments, the deep sea, estuaries, shallow coastal waters, lakes, rivers and underground waters. They are primarily marine and fewer than ten percent are found in freshwater. There are about 72 freshwater species in total, being predominantly found in the [[Palearctic realm|Palearctic]] and [[Neotropical realm]]s. These non-marine mysids occur in four distinct types of habitats; some are estuarine species; some were isolated in the [[Ponto-Caspian Basin]] where ''[[Paramysis]]'' has since radiated enormously (23 species); some are glacial [[Relict (biology)|relicts]] and some are subterranean [[Tethys Ocean|Tethyan]] relicts.<ref>{{cite journal |author1=Porter, Megan L. |author2=Meland, Kenneth |author3=Price, Wayne |year=2008 |title=Global diversity of mysids (Crustacea-Mysida) in freshwater |journal=Developments in Hydrobiology |volume=198 |pages=213–218 |doi=10.1007/978-1-4020-8259-7_23 |isbn=978-1-4020-8258-0 }}</ref>

==Behavior==
[[File:Mysis relicta..jpg|thumb|left|''Mysis relicta'']]
Some species are [[benthic]] (living on the seabed) and others [[pelagic]] (living in mid-water), but most are found close to, crawling on or burrowing into the mud or sand. Most marine species are benthic by day but leave the seabed at night to become [[plankton]]ic. Locomotion is mostly by swimming, the pleopods being used for this purpose. Some mysids live among [[algae]] and [[seagrass]]es, some are solitary while many form dense swarms. Mysids form an important part of the diet of such fish as [[shad]] and [[flounder]].<ref name=Ruppert/> In general, they are free-living, but a few species, mostly in the subfamily [[Heteromysinae]], are [[commensal]] and are associated with [[sea anemone]]s and [[hermit crab]]s.<ref name="Meland"/> Several [[taxon|taxa]] have also been described from different freshwater habitats and caves.<ref name="Meland"/> ''[[Mysis relicta]]'' and its close relatives inhabit cold, deep lakes and have a diurnal cycle of vertical migrations.<ref>{{cite journal |author1=Audzijonytė, Asta |author2=Väinölä, Risto |year=2005 |title=Diversity and distributions of circumpolar fresh- and brackish-water ''Mysis'' (Crustacea: Mysida): descriptions of ''M. relicta'' Lovén, 1862, ''M. salemaai'' n.sp., ''M. segerstralei'' n.sp. and ''M. diluviana'' n.sp., based on molecular and morphological characters |journal=Hydrobiologia |volume=544 |issue=1 |pages=89–141 |doi=10.1007/s10750-004-8337-7|s2cid=20925048 }}</ref> The species ''Mysidium integrum'' has a [[Mutualism (biology)|mutualistic]] relationship with [[longfin damselfish]], the shrimp providing nutrients for the algae farms the fish feed on and the fish providing protection from predators.<ref>{{cite web |url=https://theconversation.com/we-found-algae-farming-fish-that-domesticate-tiny-shrimp-to-help-run-their-farms-151615 |title=We found algae-farming fish that domesticate tiny shrimp to help run their farms |date=2020-12-08}}</ref><ref>{{cite journal |doi=10.1038/s41467-020-19958-5|title=Domestication via the commensal pathway in a fish-invertebrate mutualism|year=2020|last1=Brooker|first1=Rohan M.|last2=Casey|first2=Jordan M.|last3=Cowan|first3=Zara-Louise|last4=Sih|first4=Tiffany L.|last5=Dixson|first5=Danielle L.|last6=Manica|first6=Andrea|last7=Feeney|first7=William E.|journal=Nature Communications|volume=11|issue=1|page=6253|pmid=33288750|pmc=7721709|bibcode=2020NatCo..11.6253B |s2cid=227948531|doi-access=free}}</ref>

The majority of Mysida are [[omnivore]]s, feeding on algae, [[detritus]], and [[zooplankton]]. [[Scavenger|Scavenging]] and [[cannibalism]] are also common, with the adults sometimes preying on their young once they emerge from the marsupium.<ref name="Mauchline"/> The pelagic and most other species are [[filter feeder]]s, creating a feeding current with the exopods of their pereopods. This wafts food particles into a ventral food groove along which they are passed before being filtered by [[seta]]e (bristles) on the second maxillae. Larger planktonic prey can be caught in a trap composed of the endopods of the thoracic appendages.<ref name=Ruppert/> Some benthic species, especially members of the subfamily [[Erythropinae]], have been observed feeding on small particles which they collected by grooming the surfaces of their bodies and legs.<ref name="Meland"/>

[[File:Brackwasserkrebs, Spaltfußkrabbe (Mysis vulgaris).jpg|thumb|''[[Neomysis integer]]'']]
Individual mysids are either male or female, and fertilisation is external. The [[gonad]]s are in the thorax and are tubular in shape. Males have two [[gonopore]]s in the eighth thoracic segment and a pair of long penises. The female gonopores are in the sixth thoracic segment and the oostegites are attached to the first to seventh pereopods to form a brood pouch.<ref name=Ruppert/> Mating usually takes place at night and lasts only a few minutes.<ref name="Mauchline"/> During the process, the male inserts his penises into the marsupium and releases sperm. This stimulates the female and the eggs are usually released into the marsupium within an hour. Here they are fertilised and retained, development of the embryos in the brood pouch being [[Direct development|direct]] with the young hatching from the eggs as miniature adults.<ref name=Ruppert/> The size of a mysid brood generally correlates with body length and environmental factors such as density and food availability.<ref name="Dom 1999">{{cite journal |author1=Domingues, P. M. |author2=Turk, P. E. |author3=Andrade, J. P. |author4=Lee, P. G. |year=1999 |title=Culture of the mysid, ''Mysidopsis almyra'' (Bowman), (Crustacea: Mysidacea) in a static water system: effects of density and temperature on production, survival and growth |journal=[[Aquaculture Research]] |volume=30 |issue=2 |pages=135–143 |doi=10.1046/j.1365-2109.1999.00309.x|doi-access=free }}</ref> The age at which mysids reach [[sexual maturity]] depends on water temperature and food availability.<ref name="Dom 1999"/><ref name= "Sudo">{{cite journal |author=Sudo, H. |year=2003 |title=Effect of temperature on growth, sexual maturity and reproduction of ''Acanthomysis robusta'' (Crustacea: Mysidacea) reared in the laboratory |journal=[[Marine Biology (journal)|Marine Biology]] |volume=143 |issue=6 |pages=1095–1107 |doi=10.1007/s00227-003-1160-2|s2cid=83480469 }}</ref><ref name="EPA"/> For the species ''[[Americamysis bahia|Mysidopsis bahia]]'', this is normally at 12 to 20 days.<ref name="EPA">{{cite book |publisher=[[United States Environmental Protection Agency|Environmental Protection Agency]] |year=1990 |title=Culturing ''Mysidopsis bahia''. Supplemental Report. EPA 505/8-90-006b}}</ref> The young are released soon afterwards, and although their numbers are usually low, the short [[reproductive cycle]] of mysid adults means a new brood can be produced every four to seven days.<ref name="Mauchline"/><ref name="EPA"/><ref name="Dom 1998">{{cite journal |author1=Domingues, Pedro M. |author2=Turk, Philip E. |author3=Andrade, Jose P. |author4=Lee, Philip G. |year=1998 |title=Pilot-scale production of mysid shrimp in a static water system |journal=[[Aquaculture International]] |volume=6 |issue=5 |pages=387–402 |doi=10.1023/A:1009232921784|s2cid=37703503 }}</ref>

==Uses==
Some species of mysids are easy to culture on a large scale in the laboratory as they are highly adaptive, and can tolerate a wide range of conditions. Despite low [[fecundity]], these species have a short reproductive cycle which means they can quickly reproduce in vast numbers.<ref name="Mauchline"/><ref name="Dom 1998"/> They can be cultured in static or flow-through systems, the latter having been shown to be able to maintain a higher stocking density than a static system.<ref name="Lussier">{{cite journal |author1=Lussier, Suzanne M. |author2=Kuhn, Anne |author3=Chammas, Melissa J. |author4=Sewall, John |year=1988 |title=Techniques for the laboratory culture of ''Mysidopsis'' species (Crustacea: Mysidacea) |journal=[[Environmental Toxicology and Chemistry]] |volume=7 |issue=12 |pages=969–977 |doi=10.1002/etc.5620071203}}</ref> In flow-through systems, juvenile mysids are continuously separated from the adult brood stock in order to reduce mortality due to cannibalism.<ref name="Dom 1999"/> ''[[Artemia]]'' ([[brine shrimp]]) juveniles (incubated for 24 hours) are the most common food in mysid cultures, sometimes enriched with highly unsaturated [[fatty acid]]s to increase their nutritional value.<ref name="Dom 1999"/>

Cultured mysids are thought to provide an ideal food source for many marine organisms. They are often fed to [[cephalopod]]s, fish larvae, and commercial [[shrimp farming|farmed shrimp]] due to their small size and low cost.<ref name="Dom 1999"/><ref name="woods 2005">{{cite journal |author=Woods, Chris M. C. |year=2005 |title=Growth of cultured seahorses (''Hippocampus abdominalis'') in relation to feed ration |journal=Aquaculture International |volume=13 |issue=4 |pages=305–314 |doi=10.1007/s10499-004-3100-7|s2cid=42514195 }}</ref><ref name="Woods 2003">{{cite journal |author1=Woods, Chris M. C. |author2=Valentino, Fiamma |year=2003 |title=Frozen mysids as an alternative to live ''Artemia'' in culturing seahorses ''Hippocampus abdominalis'' |journal=Aquaculture Research |volume=34 |issue=9 |pages=757–763 |url=http://www.aseanbiotechnology.info/Abstract/21008703.pdf |archive-url=https://web.archive.org/web/20110721094438/http://www.aseanbiotechnology.info/Abstract/21008703.pdf |url-status=usurped |archive-date=July 21, 2011 |doi=10.1046/j.1365-2109.2003.00882.x}}</ref><ref name="Vidal">{{cite journal |author1=Vidal, E. A. G. |author2=DiMarco, F. P. |author3=Wormuth, J. H. |author4=Lee, P. G. |year=2002 |title=Optimizing rearing conditions of hatchling loliginid squid |journal=[[Marine Biology (journal)|Marine Biology]] |volume=140 |pages=117–127 |doi=10.1007/s002270100683|s2cid=85108374 }}</ref> Their high protein and fat content also makes them a good alternative to live enriched ''Artemia'' when feeding juveniles (especially those that are difficult to maintain such as young [[seahorse]]s) and other small fauna.<ref name="Woods 2003"/><ref name="Vidal"/>

Their sensitivity to water quality also makes them suitable for [[bioassay]]s. ''[[Americamysis bahia]]'' and ''[[Americamysis almyra]]'' are frequently used to test for [[pesticide]]s and other toxic substances, with ''A. bahia'' found to be more sensitive during the periods when it is [[ecdysis|moulting]].<ref>{{cite journal |author1=Nimmo, D. R. |author2=Hamaker, T. L. |year=1982 |title=Mysids in toxicity testing – a review |journal=[[Hydrobiologia]] |volume=93 |issue=1–2 |pages=171–178 |doi=10.1007/BF00008110|s2cid=44057913 }}</ref>

==Systematics==
The Mysida belong to the superorder Peracarida, which means "near to shrimps". Although in many respects mysids appear similar to some shrimps, the main characteristic separating them from the superorder [[Eucarida]] is their lack of free-swimming [[crustacean larvae|larvae]].<ref name="Mauchline">{{cite book |author=Mauchline, J. |year=1980 |title=The Biology of Mysids and Euphausiids |editor1=Blaxter, J. H. S. |editor2=Russell, F. S. |editor2-link=Russell, F. S. |editor3=Yonge, M. |series=Advances in Marine Biology: Volume 18 |publisher=[[Academic Press]] |isbn=978-0-08-057941-2 }}</ref> The order Mysida is extensive and currently includes approximately 160 [[genus|genera]], containing more than 1000 species.<ref name="Meland">{{cite web |author=Meland, Kenneth |url=http://crustacea.net/crustace/mysidacea/index.htm |title=Mysidacea: Families, Subfamilies and Tribes |date=October 2, 2000 |publisher=[[Australian Museum]] |access-date=2010-09-07}}</ref>

Traditionally, Mysida were united with another, externally similar group of pelagic crustaceans, the [[Lophogastrida]], into a broader order [[Mysidacea]], but that classification is generally abandoned at present.<ref name=WoRMS/><ref name=Brusca>Brusca, R.; Brusca, G. (2003). Invertebrates. Sunderland, Massachusetts: Sinauer Associates</ref><ref>{{cite book |url=http://atiniui.nhm.org/pdfs/3839/3839.pdf |title=An Updated Classification of the Recent Crustacea |author1=Martin, Joel W. |author2=Davis, George E. |year=2001 |publisher=[[Natural History Museum of Los Angeles County]] |access-date=2010-11-03 |archive-date=2011-07-11 |archive-url=https://web.archive.org/web/20110711181351/http://atiniui.nhm.org/pdfs/3839/3839.pdf |url-status=dead }}</ref><ref>[http://www.tafi.org.au/zooplankton/imagekey/malacostraca/peracarida/ Peracarida fact sheet - Guide to the marine zooplankton of south eastern Australia] {{webarchive|url=https://web.archive.org/web/20111004050244/http://www.tafi.org.au/zooplankton/imagekey/malacostraca/peracarida/ |date=2011-10-04 }}</ref><ref name=Anderson>Anderson, Gary (2010-01-20): [http://peracarida.usm.edu/iwp_home.html  Peracarida Taxa and Literature (Cumacea, Lophogastrida, Mysida, Stygiomysida and Tanaidacea)] {{webarchive|url=https://web.archive.org/web/20100124195537/http://peracarida.usm.edu/iwp_home.html |date=2010-01-24 }}</ref>
While the previous grouping had good [[morphology (biology)|morphological]] support, [[molecular systematics|molecular studies]] do not corroborate the [[monophyly]] of this group.<ref name=Mel>{{cite journal |author1=Meland, K. |author2=Willassen, E. |year=2007 |url=http://decapoda.nhm.org/pdfs/31293/31293.pdf |title=The disunity of "Mysidacea" (Crustacea) |journal=[[Molecular Phylogenetics and Evolution]] |volume=44 |issue=3 |pages=1083–1104 |pmid=17398121 |doi=10.1016/j.ympev.2007.02.009}}</ref> Previously Mysida included two other families, [[Lepidomysidae]] and [[Stygiomysidae]], but these have now been placed in a separate order, [[Stygiomysida]].<ref name=Mel/>

==Classification==
{{col-begin}}
{{col-2}}
*Family [[Mysidae]]<small> Haworth, 1825</small><ref>{{cite WoRMS |author=Mees, J. |year=2013 |title=Mysidae Haworth, 1825 |id=119822 |access-date=2014-01-30 }}</ref>
**Subfamily [[Boreomysinae]]<small> Holt & Tattersall, 1905</small>
***2 genera
**Subfamily [[Erythropinae]]<small> Hansen, 1910</small>
***54 genera
**Subfamily [[Gastrosaccinae]]<small> Norman, 1892</small>
***10 genera
**Subfamily [[Heteromysinae]]<small> Norman, 1892</small>
***14 genera
**Subfamily [[Leptomysinae]]<small> Hansen, 1910</small>
***30 genera
**Subfamily [[Mysidellinae]]<small> Czerniavsky, 1882</small>
***2 genera
**Subfamily [[Mysinae]]<small> Haworth, 1825</small>
***55 genera
**Subfamily [[Palaumysinae]]<small> Wittmann, 2013</small>
***1 genus
**Subfamily [[Rhopalophthalminae]]<small> Hansen, 1910</small>
***1 genus
**Subfamily [[Siriellinae]]<small> Norman, 1892</small>
***3 genera

{{col-2}}
*Family [[Petalophthalmidae]]<small> Czerniavsky, 1882</small><ref>{{cite WoRMS |author=Mees, J. |year=2013 |title=Petalophthalmidae Czerniavsky, 1882 |id=119823 |access-date=2014-01-30 }}</ref>
**Genus ''[[Bacescomysis]]''<small> Murano & Krygier, 1985</small>
**Genus ''[[Ceratomysis]]''<small> Faxon, 1893</small>
**Genus ''[[Hansenomysis]]''<small> Stebbing, 1893</small>
**Genus ''[[Parapetalophthalmus]]''<small> Murano & Bravo, 1998</small>
**Genus ''[[Petalophthalmus]]''<small> Willemoes-Suhm, 1875</small>
**Genus ''[[Pseudopetalophthalmus]]''<small> Bravo & Murano, 1997</small>
{{col-end}}

==External links==
{{Portal|Crustaceans}}
*{{Wikispecies-inline|Mysida}}

==References==
{{Reflist|25em}}

{{Malacostraca}}

{{Taxonbar|from=Q13411080}}

[[Category:Mysida| ]]
[[Category:Crustacean orders]]