Editing Notostraca

{{Short description|Order of small freshwater animals}}
{{Automatic taxobox
| name = Notostraca
| image = Triops australiensis.JPG
| image_caption = ''[[Triops australiensis]]''
| image2 = LepidurusApus.jpg
| image2_caption = ''[[Lepidurus apus]]''
| fossil_range = {{fossil range|Famennian|Recent}}
| taxon = Notostraca
| authority = [[Georg Ossian Sars|G. O. Sars]], 1867
| subdivision_ranks = Genera
| subdivision = *''[[Lepidurus]]'' <small>Leach, 1819</small>
*''[[Triops]]'' <small>Schrank, 1803</small>
*Fossil genera and species, see text
}}
The order '''Notostraca''', containing the single family '''Triopsidae''', is a group of [[crustacean]]s known as '''tadpole shrimp'''<ref name="Light"/> or '''shield shrimp'''.<ref name="Lowry">{{cite web |url=http://crustacea.net/crustace/www/notostra.htm |author=J. K. Lowry |work=Crustacea, the Higher Taxa: Description, Identification, and Information Retrieval |date=October 2, 1999 |title=Notostraca (Branchiopoda) |access-date=February 7, 2011 |archive-url=https://web.archive.org/web/20110723062941/http://crustacea.net/crustace/www/notostra.htm |archive-date=July 23, 2011 |url-status=dead }}</ref> The two genera, ''[[Triops]]'' and ''[[Lepidurus]]'', are considered [[living fossil]]s, with similar forms having existed since the end of the [[Devonian]], around 360 million years ago. They have a broad, flat [[carapace]], which conceals the head and bears a single pair of compound eyes. The abdomen is long, appears to be segmented and bears numerous pairs of flattened legs. The [[telson]] is flanked by a pair of long, thin caudal rami. [[Phenotypic plasticity]] within taxa makes species-level identification difficult, and is further compounded by variation in the mode of reproduction. Notostracans are [[omnivore]]s living on the bottom of [[temporary pool]]s and shallow lakes.

==Description==
Notostracans are {{convert|2|-|5|cm|1}} long, with a broad [[carapace]] at the front end, and a long, slender abdomen.<ref name="Light">{{cite book |author=Denton Belk |chapter=Branchiopoda |editor1=Sol Felty Light |editor2=James T. Carlton |year=2007 |title=The Light and Smith Manual: Intertidal Invertebrates from Central California to Oregon |edition=4th |publisher=[[University of California Press]] |isbn=978-0-520-23939-5 |pages=414–417 |chapter-url=https://books.google.com/books?id=64jgZ1CfmB8C&pg=PA417}}</ref> This gives them a similar overall shape to a [[tadpole]], from which the [[common name]] ''tadpole shrimp'' derives.<ref name="Light"/> The carapace is dorso-ventrally flattened, smooth, and bears no [[rostrum (anatomy)|rostrum]]; it includes the head, and the two sessile [[compound eye]]s are located together on top of the head.<ref name="Light"/> The two pairs of [[antenna (biology)|antennae]] are much reduced, with the second pair sometimes missing altogether.<ref name="Lowry"/> The [[arthropod mouthparts|mouthparts]] comprise a pair of uniramous [[Mandible (arthropod mouthpart)|mandibles]] and no maxillipeds.<ref name="Lowry"/>

[[File:Triops australiensis belly.jpg|thumb|left|The ventral side of ''Triops australiensis'', showing the many pairs of phyllopodous legs]]
The trunk consists of three regions; thorax I, thorax II and the abdomen. Thorax I is made up of 11 segments, each with a pair of well-developed [[arthropod leg|limbs]] and the genital opening on the eleventh segment. In the female, it is modified to form a "brood pouch".<ref name="Pennak"/> The first one or two pairs of legs differ from the remainder, and probably function as sensory organs.<ref name="Pennak">{{cite book |author=Douglas Grant Smith |year=2001 |title=Pennak's freshwater invertebrates of the United States: Porifera to Crustacea |edition=4th |publisher=[[John Wiley and Sons]] |isbn=978-0-471-35837-4 |url=https://books.google.com/books?id=GqIctb8IqPoC&pg=PA431}}</ref>

The somites on thorax II are fused into "rings", which varies in number between species and gender and appear to be [[Segmentation (biology)|body segments]], but do not always reflect the underlying segmentation.<ref name="Light"/> Each ring is made up of 2–6 complete or partial fused segments, and the number of legs on each body ring match its number of segments.<ref>[https://academic.oup.com/book/38957/chapter-abstract/350633934?redirectedFrom=fulltext&login=false Evolution and Phylogeny of Pancrustacea: A Story of Scientific Method - 44. Notostraca and Allies (Calmanostraca)]</ref><ref name="Light"/> The legs become progressively smaller posteriorly,<ref name="Pennak"/> with the last segments being legless.<ref name="Light"/>

The limbless abdomen ends in a [[telson]] and a pair of long, thin, multi-articulate [[Caudal ramus|caudal rami]].<ref>{{cite book |title=The Invertebrata |edition=4th |year=1961 |publisher=[[Cambridge University Press]] |chapter=Subclass 1. Branchiopoda |pages=368–375 |chapter-url=https://books.google.com/books?id=7FM8AAAAIAAJ&pg=PA373}}</ref> The form of the telson varies between the two genera: in ''[[Lepidurus]]'', a rounded projection extends between the caudal rami, while in ''[[Triops]]'' there is no such projection.<ref name="Light"/>

==Life cycle==
[[File:Collected Eggs of Triops Longicaudatus.JPG|thumb|right|A collection of lake sediment containing the pink eggs of ''Triops longicaudatus'']]
Within the Notostraca, and even within species, there is variation in the mode of reproduction, with some populations [[sexual reproduction|reproducing sexually]], some showing [[self-fertilisation]] of females, and some showing a [[Androdioecy|mix of the two]].<ref name="Light"/><ref>[https://academic.oup.com/jhered/article/107/6/518/2622894?login=false Self-Fertilization and the Role of Males in Populations of Tadpole Shrimp (Branchiopoda: Notostraca: Triops)]</ref> The frequency of males in populations is therefore highly variable.<ref name="Pennak"/> In sexual populations, the [[sperm]] leave the male's body through simple pores, there being no [[penis]]. The eggs are released by the female and then held in the cup-like brood pouch.<ref name="Pennak"/> The eggs are retained by the female only for a short time before being laid,<ref name="Ax"/> and the [[crustacean larvae|larvae]] develop directly, without passing through a [[metamorphosis]].<ref name="Lowry"/>

==Ecology and distribution==
Notostracans are [[omnivore|omnivorous]], eating small animals such as [[fish]]es and [[fairy shrimp]].<ref name="Light"/> They are found worldwide in [[freshwater]], [[brackish water]], or [[Saline water|saline]] pools, as well as in shallow [[lake]]s, [[peat bog]]s, and [[moorland]].<ref name="Lowry"/> The species ''[[Triops longicaudatus]]'' is considered an [[pest (organism)|agricultural pest]] in [[California]] [[Paddy field|rice paddies]], because it prevents light from reaching the rice seedlings by stirring up sediment.<ref>{{cite book |first=Hugh F. |last=Clifford |year=1991 |title=Aquatic Invertebrates of Alberta: An illustrated guide |publisher=[[University of Alberta]] |isbn=978-0-88864-234-9 |chapter=Notostraca: Tadpole shrimp |pages=144–145 |chapter-url=https://books.google.com/books?id=8UQ4jHev6voC&pg=PA144}}</ref>

==Evolution and fossil record==
The [[fossil record]] of Notostraca is extensive, occurring in a wide range of geological deposits.<ref>{{cite book |author1=Atte Korhola  |author2=Milla Rautio  |name-list-style=amp |year=2001 |chapter=Cladocera and other branchiopod crustaceans |pages=5–41 |editor1=John P. Smol |editor2=Harry John Betteley Birks |editor3=William M. Last |title=Tracking Environmental Change Using Lake Sediments. Volume 4: Zoological Indicators |publisher=[[Kluwer Academic Publishers]] |isbn=978-1-4020-0658-6 |chapter-url=https://books.google.com/books?id=p-bwPq3P1YwC&pg=PA30}}</ref> The oldest known notostracan is the species ''[[Strudops|Strudops goldenbergi]]'' from the Late [[Devonian]] ([[Famennian]] ~ 365 million years ago) of Belgium.<ref>{{Cite journal|last1=Lagebro|first1=Linda|last2=Gueriau|first2=Pierre|last3=Hegna|first3=Thomas A.|last4=Rabet|first4=Nicolas|last5=Butler|first5=Aodhán D.|last6=Budd|first6=Graham E.|date=May 2015|editor-last=Korn|editor-first=Dieter|title=The oldest notostracan (Upper Devonian Strud locality, Belgium)|journal=Palaeontology|language=en|volume=58|issue=3|pages=497–509|doi=10.1111/pala.12155|s2cid=129231634|issn=0031-0239|doi-access=free|bibcode=2015Palgy..58..497L }}</ref> The lack of major morphological change since {{Ma|250}} has led to Notostraca being described as [[living fossil]]s.<ref name="Diversity"/> [[Kazacharthra]], a group known only from [[Triassic]] and [[Jurassic]] fossils from [[Kazakhstan]] and Western [[China]],<ref name=Liu>{{cite journal|last=Liu|first=Hongfu|journal=Acta Palaeontologica Sinica|year=1996|volume=4|issue=35|pages=490–494|url=http://europepmc.org/abstract/CBA/295478/reload=0;jsessionid=ZLmTAb0szp8TXnYtpqjL.4|archive-url=https://archive.today/20130414172059/http://europepmc.org/abstract/CBA/295478/reload=0;jsessionid=ZLmTAb0szp8TXnYtpqjL.4|url-status=dead|archive-date=2013-04-14|title=New materials of Late Triassic Kazacharthra from Xinjaing}}</ref> are closely related to notostracans, and may belong within the order Notostraca,<ref>{{cite book |author=Marjorie L. Reaka-Kudla |year=2002 |chapter=Habitat specialization and its relation to conservation policy in Crustacea |pages=211–221 |editor=Elva Escobar-Briones |editor2=Fernando Alvarez |title=Modern Approaches to the Study of Crustacea |publisher=[[Springer Science+Business Media|Springer]] |isbn=978-0-306-47366-1}}</ref> or alternatively are placed as their sister group within the clade Calmanostraca.

The "central autapomorphy" of the Notostraca is the abandonment of [[filter feeder|filter feeding]] in open water, and the development of a benthic lifestyle in muddy waters, taking up food from particles of sediment and preying on small animals.<ref name="Ax">{{cite book |author=Peter Ax |year=2000 |title=Multicellular Animals. The Phylogenetic System of the Metazoa. Volume II |publisher=[[Springer Science+Business Media|Springer]] |isbn=978-3-540-67406-1|chapter=Notostraca |pages=158–159 |chapter-url=https://books.google.com/books?id=FweHI7uZ198C&pg=PA158}}</ref> A number of other characteristics are correlated with this change, including the increased size of the animal compared to its relatives, and the loss of the ability to hinge the carapace; although a central keel marks the former separation into two valves, the [[Adduction|adductor muscle]] is missing.<ref name="Ax"/> Notostracans retain the [[plesiomorphy|plesiomorphic]] condition of having two separate compound eyes, which abut, but have not become united, as seen in other groups of Branchiopoda.<ref name="Ax"/>
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The metamerism of the trunk of Notostraca is unique. Whereas each of the first eleven thoracic segments in them has one pair of limbs, the next 16 to 20 segments have several pairs each - from two to six pairs on each segment, the number of pairs per segment increasing rearward while the size of the limbs decreases. Such polypody is a unique phenomenon. It is usually attributed to fusion of segments or to their failure to develop. F. Linder states that in the postembryonic development of Conchostraca the individualisation of each new segment begins on the ventral side, and in some cases is not completed: the author attributed the polypody of Notostraca to that process. In fact, not only the limbs of Notostraca but also other metameric organs on their ventral side are subject to 'multiplication': the metamerism of the ventral nerve chain and the ventral muscles agrees with the metamerism of the limbs, and not with that of the cuticle and of the longitudinal musculature of the dorsal side of the body. Apart from their polypody, the postgenital thoracic segments of Notostraca differ considerably from the pregenital segments, in both the structure of their musculature and that of the peripheral nerves innervating it. Because of all these differences, carcinologists often regard only the pregenital segments of Notostraca and Conchostraca as thoracic, and classify all the rest as abdominal. The last four to fifteen segments of the body of Notostraca have no limbs ..., which ends in the anal lobe, with paired filamentous cerci. The separate species of Notostraca differ among themselves in the number of postgenital (polypodous) segments, the number of limbs, and the number of limbless abdominal segments; these numbers vary even within each separate species. Inconstancy of numbers of body segments within a species is a very primitive feature, and very rare among arthropods; except for Notostraca and Conchostraca, such inconstancy is known only among some trilobites and myriapods.
<ref>{{cite book |author=D. R. Khanna |year=2004 |title=Biology of Arthropoda |publisher=[[Discovery Publishing House]] |isbn=978-81-7141-897-8 |chapter=Segmentation in arthropods |pages=316–394 |url=https://books.google.com/books?id=Hd4OEDo4gbwC&pg=PA349}}</ref>
-->

==Taxonomy==
The extant members of [[order (biology)|order]] Notostraca composed a single [[family (biology)|family]], Triopsidae, with only two [[genus|genera]], ''[[Triops]]'' and ''[[Lepidurus]]''.<ref name="Diversity"/>
The problematic Middle Ordovician fossil ''[[Douglasocaris]]'' has been erected and placed in its own family Douglasocaridae by Caster & Brooks 1956, and may be ancestral to Notostraca.

The [[phenotypic plasticity]] shown by notostracan species make identification to the species level difficult.<ref name="Diversity">{{cite book |author=Luc Brendonck |author2=D. Christopher Rogers |author3=Jorgen Olesen |author4=Stephen Weeks |author5=Walter R. Hoch |name-list-style=amp |year=2008 |chapter=Global diversity of large branchiopods (Crustacea: Branchiopoda) in freshwater |journal=[[Hydrobiologia]] |volume=595 |issue=1 |pages=167–176 |doi=10.1007/s10750-007-9119-9 |title=Freshwater Animal Diversity Assessment |editor1=Estelle V. Balian |editor2=Christian Lévêque |editor3=Hendrik Segers |editor4=Koen Martens |series=Developments in Hydrobiology 198 |isbn=978-1-4020-8258-0|s2cid=46608816 }}</ref> Many putative species have been described based on morphological variation, such that by the 1950s, as many as 70 species were recognised.<ref name="Diversity"/> Two important revisions – those of Linder in 1952<ref>{{cite journal |author=Folke Linder |year=1952 |title=Contributions to the morphology and taxonomy of the Branchiopoda Notostraca, with special reference to the North American species |journal=[[Proceedings of the United States National Museum]] |volume=102 |issue=3291 |pages=1–69 |url=http://biostor.org/reference/3963 |doi=10.5479/si.00963801.102-3291.1}}</ref> and Longhurst in 1955<ref>{{cite journal |author=Alan R. Longhurst |year=1955 |title=A review of the Notostraca |journal=[[Bulletin of the British Museum (Natural History)]] |volume=3 |issue=1 |pages=1–57 |url=http://biostor.org/reference/1299|doi=10.5962/bhl.part.4119 |doi-access=free }}</ref> – [[synonym (taxonomy)|synonymised]] many taxa, and resulted in the recognition of only 11 species in the two genera. This taxonomy was accepted for decades,<ref name="Diversity"/> "even attaining the status of dogma".<ref>{{cite journal |author=Clay Sassaman |author2=Marie A. Simovich |author3=Michael Fugate |name-list-style=amp |year=1997 |title=Reproductive isolation and genetic differentiation in North American species of ''Triops'' (Crustacea: Branchiopoda: Notostraca) |journal=[[Hydrobiologia]] |volume=359 |issue=1–3 |pages=125–147 |doi=10.1023/A:1003168416080|s2cid=6767325 }}</ref> More recent studies, especially those employing [[molecular phylogenetics]], have shown that the eleven currently recognised species conceal a greater number of reproductively isolated populations.<ref name="Diversity"/>

=== Genera list ===

* ''[[Apudites]]'', ''(Formerly "Notostraca" minor,'' often referred to as ''Triops cancriformis minor,'' or "''Triops" minor'' in historic literature) Lower Triassic, [[Grès à Voltzia]], [[Vosges Mountains]], France; [[Hassberge Formation]], Germany, Late Triassic ([[Carnian]])<ref>{{Cite journal|last1=Wagner|first1=Philipp|last2=Haug|first2=Joachim T.|last3=Sell|first3=Jürgen|last4=Haug|first4=Carolin|date=December 2017|title=Ontogenetic sequence comparison of extant and fossil tadpole shrimps: no support for the "living fossil" concept|url=http://link.springer.com/10.1007/s12542-017-0370-8|journal=PalZ|language=en|volume=91|issue=4|pages=463–472|doi=10.1007/s12542-017-0370-8|bibcode=2017PalZ...91..463W |s2cid=90922613|issn=0031-0220|url-access=subscription}}</ref><ref name=":1">{{Cite journal |last=Geyer |first=Gerd |last2=Hegna |first2=Thomas A. |last3=Kelber |first3=Klaus-Peter |date=2024 |title=The end of the ‘living fossil’ tale? A new look at Triassic specimens assigned to the tadpole shrimp Triops cancriformis (Notostraca) and associated phyllopods from the Vosges region (eastern France) |url=https://onlinelibrary.wiley.com/doi/full/10.1002/spp2.1589 |journal=Papers in Palaeontology |volume=10 |issue=5 |at=e1589 |doi=10.1002/spp2.1589 |doi-access=free |url-access=subscription }}</ref>
* ''[[Brachygastriops]]'' Dabeigou Formation, China, Late Jurassic or Early Cretaceous
* ''[[Chenops]]'' [[Yixian Formation]], China, Early Cretaceous ([[Aptian]])
* ''[[Dikelocephala]]'',  Lower Triassic of North China
* ''[[Discocephala]]'', Lower Triassic of North China
* ''[[Heidiops]]'', Lower Permian of the [[Lodève Basin]], France<ref name=":2">{{Cite journal |last=Werneburg |first=R. |last2=Schneider |first2=J. W. |date=2023 |title=New branchiopod crustaceans from the late Carboniferous and early Permian of the Thuringian Forest Basin, Germany, with a review of Permian notostracans from the Lodève basin, France |url=https://www.researchgate.net/publication/365839036_New_branchiopod_crustaceans_from_the_late_Carboniferous_and_early_Permian_of_the_Thuringian_Forest_Basin_Germany_with_a_review_of_Permian_notostracans_from_the_Lodeve_basin_France |journal=Semana |volume=37 |pages=57–103}}</ref>
* ''[[Jeholops]]'' Yixian Formation, China, Early Cretaceous (Aptian)
* ''[[Lynceites]]'' Germany, Canada, Carboniferous
* ''[[Prolepidurus]]'', Late Jurassic?-Lower Cretaceous, [[Transbaikal]], Russia
* ''[[Strudops]]'' Strud locality, Belgium, late Devonian (Fammenian)
* ''[[Thuringiops]]'', Upper [[Oberhof Formation]], [[Thuringian Forest Basin]], Carboniferous Germany<ref name=":2" />
* ''[[Weichangiops]]'' [[Dabeigou Formation]], China, Late Jurassic or Early Cretaceous
* ''[[Xinjiangiops]]'' Kelamayi Formation, China, Middle Triassic

''Incertae sedis'' species

* ''"Notostraca" oleseni'' Yixian Formation, China, Early Cretaceous (Aptian)<ref name=":0">{{Cite journal|last1=Wagner|first1=Philipp|last2=Haug|first2=Joachim T.|last3=Haug|first3=Carolin|date=December 2019|title=A new calmanostracan crustacean species from the Cretaceous Yixian Formation and a simple approach for differentiating fossil tadpole shrimps and their relatives|journal=Zoological Letters|language=en|volume=5|issue=1|pages=20|doi=10.1186/s40851-019-0136-0|issn=2056-306X|pmc=6582493|pmid=31245037 |doi-access=free }}</ref>
* ''"Calmanostraca" hassbergella'' Hassberge Formation, Germany, Late Triassic (Carnian)<ref name=":0" />

==See also==
* [[Trilobite]]

==References==
{{Reflist|32em}}

==External links==
{{Commons category}}
{{Wikispecies}}
* {{ARKive|3=''Triops cancriformis''}}
* {{cite web |url=http://www.ipm.ucdavis.edu/PMG/r682500111.html |title=Tadpole shrimp. Scientific name: ''Triops longicaudatus'' |work=UC Pest Management Guidelines |publisher=[[University of California, Davis]] |date=February 2009 |author1=L. D. Godfrey  |author2=L. A. Espino |name-list-style=amp }}

{{Branchiopoda}}
{{Taxonbar|from=Q3344541}}
{{Authority control}}

[[Category:Notostraca| ]]
[[Category:Freshwater crustaceans]]
[[Category:Cisuralian taxonomic orders]]
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