Caridea

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The Caridea, commonly known as caridean shrimp or true shrimp, from the Greek word καρίς, καρίδος (karís, karídos, “shrimp”), are an infraorder of shrimp within the order Decapoda. This infraorder contains all species of true shrimp. They are found widely around the world in both fresh and salt water. Many other animals with similar names – such as the mud shrimp of Axiidea and the boxer shrimp of Stenopodidea – are not true shrimp, but many have evolved features similar to true shrimp.

BiologyEdit

Carideans are found in every kind of aquatic habitat, with the majority of species being marine. Around a quarter of the described species are found in fresh water, however, including almost all the members of the species-rich family Atyidae and the Palaemonidae subfamily Palaemoninae.<ref name="freshwater">Template:Cite journal</ref> They include several commercially important species, such as Macrobrachium rosenbergii, and are found on every continent except Antarctica.<ref name="freshwater"/> The marine species are found at depths to Template:Convert,<ref name="Chace">Template:Cite book</ref> and from the tropics to the polar regions.

In addition to the great variety in habitat, carideans vary greatly in form, from species a few millimetres long when fully grown,<ref name="SA">Template:Cite book</ref> to those that grow to over Template:Convert long.<ref name="Chace"/> Except where secondarily lost, shrimp have one pair of stalked eyes, although they are sometimes covered by the carapace, which protects the cephalothorax.<ref name="Chace"/> The carapace also surrounds the gills, through which water is pumped by the action of the mouthparts.<ref name="Chace"/>

Most carideans are omnivorous, but some are specialised for particular modes of feeding. Some are filter feeders, using their setose (bristly) legs as a sieve; some scrape algae from rocks. The snapping shrimp of the genus Alpheus snap their claws to create a shock wave that stuns prey. Many cleaner shrimp, which groom reef fish and feed on their parasites and necrotic tissue, are carideans.<ref name="Chace"/> In turn, carideans are eaten by various animals, particularly fish and seabirds, and frequently host bopyrid parasites.<ref name="Chace"/>

LifecycleEdit

Unlike Dendrobranchiates, Carideans brood their eggs rather than releasing them into the water. Caridean larvae undergo all naupliar development within the egg, and eclose as a zoea. The zoea stage feeds on phytoplankton. There can be as few as two zoea stages, (e.g. some freshwater Palaemonidae), or as many as 13, (e.g. some Pandalidae). The post-zoeal larva, often called a decapodid, resembles a miniature adult, but retains some larval characteristics. The decapodid larva will metamorphose a final time into a post-larval juvenile: a young shrimp having all the characteristics of adults.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Most adult carideans are benthic animals living primarily on the sea floor.

Common species include Pandalus borealis (the "pink shrimp"), Crangon crangon (the "brown shrimp") and the snapping shrimp of the genus Alpheus. Depending on the species and location, they grow from about Template:Convert long, and live between 1.0 and 6.5 years.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Commercial fishingEdit

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File:Wild caridean shrimp capture time series.png

Global wild capture, 1950–2010, in tonnes, of caridean shrimp<ref name=faostat>Based on data sourced from the FishStat database, FAO.</ref>

The most significant commercial species among the carideans is Pandalus borealis,<ref>Pandalus borealis (Krøyer, 1838) FAO, Species Fact Sheet. Retrieved September 2012.</ref> followed by Crangon crangon.<ref>Crangon crangon (Linnaeus, 1758) FAO, Species Fact Sheet. Retrieved September 2012.</ref> The wild-capture production of P. borealis is about ten times that of C. crangon. In 1950, the position was reversed, with the capture of C. crangon about ten times that of P. borealis.<ref name=faostat />

In 2010, the global aquaculture of all shrimp and prawn species (3.5 million tonnes) slightly exceeded the global wild capture (3.2 million tonnes).<ref name=faostat /> No carideans were significantly involved in aquaculture, but about 430,000 tonnes were captured in the wild. That is, about 13% of the global wild capture, or about 6% of the total production of all shrimp and prawns, were carideans.<ref name=faostat />

Systematics and related taxaEdit

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Shrimp of the infraorder Caridea are more closely related to lobsters and crabs than they are to the members of the sub-order Dendrobranchiata (prawns).<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Biologists distinguish these two groups based on differences in their gill structures. The gill structure is lamellar in carideans but branching in dendrobranchiates. The easiest practical way to separate true shrimp from dendrobranchiates is to examine the second abdominal segment. The second segment of a carideans overlaps both the first and the third segment, while the second segment of a dendrobranchiate overlaps only the third segment.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> They also differ in that carideans typically have two pairs of chelae (claws), while dendrobranchiates have three.<ref name="Bauer_3_14">Template:Cite book</ref> A third group, the Stenopodidea, contains around 70 species and differs from the other groups in that the third pairs of legs is greatly enlarged.<ref name="Bauer_3_14"/>

Procarididea are the sister group to the Caridea, comprising only eleven species.<ref name="Grave">Template:Cite journal</ref><ref name="Carideorum">Template:Cite journal</ref>

The cladogram below shows Caridea's relationships to other relatives within Decapoda, from analysis by Wolfe et al., 2019.<ref name="Wolfe2019">Template:Cite journal</ref>

Template:Decapoda cladogram

The below cladogram shows the internal relationships of eight selected families within Caridea, with the Atyidae (freshwater shrimp) being the most basal:<ref name="Wolfe2019"/>

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TaxonomyEdit

The infraorder Caridea is divided into 15 superfamilies:<ref name="Grave"/>

Superfamily	Image	Description
Alpheoidea	Lysmata debelius Lysmata amboinensis	Contains four families, including Alpheidae, the family of pistol or snapping shrimp, and Hippolytidae a family of cleaner shrimp.<ref name="Carideorum"/><ref>Template:Cite WoRMS</ref>
Atyoidea	Atya gabonensis Atya gabonensis	Contains one family, Atyidae, with 42 genera.<ref name="Grave"/> They are present in all tropical and most temperate waters. Adults of this family are almost always confined to fresh water.
Bresilioidea	Rimicaris kairei Rimicaris kairei	Likely to be an artificial group, containing five families<ref name="Grave"/> which may or may not be related.<ref name="M&D">Template:Cite book</ref>
Campylonotoidea		Contains two families. Fenner Chace considered it to be a sister group to the much larger superfamily Palaemonoidea (below) with which it shares the absence of endopods on the pereiopods, and a first pereiopod that is thinner than the second.<ref>Template:Cite book</ref> Using molecular phylogenetics, Bracken et al. proposed that Campylonotoidea may be closer to Atyoidea (above).<ref name="Grave"/><ref name="Bracken">Template:Cite book</ref>
Crangonoidea	Crangon crangon Crangon crangon	Contains two families: including the family Crangonidae.<ref name="Grave"/> Crangon crangon is abundant around the European coast has a sandy brown colour which it can change to match its environment. It lives in shallow water which can be slightly brackish, and it feeds nocturnally. During the day, it stays buried in the sand to escape predatory birds and fish, with only its antennae protruding.<ref name="ARKive">{{#invoke:citation/CS1\|citation	CitationClass=web }}</ref>
Galatheacaridoidea		Contains only one species, the rare Galatheacaris abyssalis. Described in 1997 on the basis of what was then a single specimen, it was seen to be so different from previously known shrimp species that a new family Galatheacarididae and superfamily Galatheacaridoidea were erected for it.<ref>Template:Cite journal</ref> Molecular phylogenetic analyses has indicated that Galatheacaris abyssalis is the larval stage of Eugonatonotus.<ref>Template:Cite journal</ref>
Nematocarcinoidea	Rhynchocinetes durbanensis Rhynchocinetes durbanensis	Contains four families.<ref name="Carideorum"/><ref>{{#invoke:citation/CS1\|citation	CitationClass=web }}</ref> They share the presence of strap-like epipods on at least the first three pairs of pereiopods, and a blunt molar process.<ref>Template:Cite book</ref> One of the families, Rhynchocinetidae, are a group of small, reclusive red-and-white shrimp. This family typically has an upward-hinged foldable rostrum,<ref name="AFD"/> hence its taxon name "Rhynchocinetidae", which means "movable beak".<ref name="AFD">{{#invoke:citation/CS1\|citation	CitationClass=web }}</ref> Pictured is Rhynchocinetes durbanensis.
Oplophoroidea	Hymenodora glacialis Hymenodora glacialis	There is only one family, Oplophoridae, of this pelagic shrimp, which contains 12 genera.<ref name="Grave"/>
Palaemonoidea	Palaemon elegans Palaemon elegans	Contains 8 families and nearly 1,000 species.<ref name="Grave"/> The position of the family Typhlocarididae is unclear, although the monophyly of a group containing the remaining seven families is well supported.<ref name="Bracken"/>
Pandaloidea	Heterocarpus ensifer Heterocarpus ensifer	Contains two families. The larger family Pandalidae has 23 genera and about 200 species, including some of commercial significance.<ref name="Grave"/>
Pasiphaeoidea		Contains one family with seven extant genera.<ref name="Grave"/>
Physetocaridoidea		Contains a single family with only one rare species, Physetocaris microphthalma.<ref name="Grave"/> Adult Physetocaris microphthalma have no eyes, and cannot form a claw because they are missing the last segment of the first pereiopod. They also have reduced gills and mouthparts, and no exopods on the pereiopods.<ref name="Bauer">Template:Cite book</ref>
Processoidea		Contains a single family comprising 65 species in 5 genera.<ref name="Grave"/> These small nocturnal shrimp live mostly in shallow seas, particularly on grass flats. The first pereiopods are usually asymmetrical, with a claw on one but not the other. The rostrum is generally a simple projection from the front of the carapace, with two teeth, one at the tip, and one further back.<ref>Template:Cite journal</ref>
Psalidopodoidea	Psalidopus huxleyi Psalidopus huxleyi	Contains a single family comprising three species, one in the western Atlantic Ocean, and two in the Indo-Pacific.<ref name="Grave"/><ref>Template:Cite journal</ref><ref name="tosaensis">Template:Cite journal</ref>
Stylodactyloidea		Contains a single family made up of five genera.<ref name="Grave"/>

Fossil recordEdit

The fossil record of the Caridean is sparse, with only 57 exclusively fossil species known.<ref name="Grave"/> The earliest of these cannot be assigned to any family, but date from the Lower Jurassic and Cretaceous.<ref>Template:Cite journal</ref> A number of extinct genera cannot be placed in any superfamily:<ref name="Grave"/> Template:Div col