Caridea - WikiHQ

The Caridea, commonly known as caridean shrimp or true shrimp (from Ancient Greek 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.

Biology

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. They include several commercially important species, such as Macrobrachium rosenbergii, and are found on every continent except Antarctica. 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, to those that grow to over long. 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 long, and live between 1.0 and 6.5 years.

Commercial fishing

upright=1.4|thumb|Global wild capture, 1950–2010, in tonnes, of caridean shrimp

The most significant commercial species among the carideans is Pandalus borealis, followed by Crangon crangon. 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. 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. They also differ in that carideans typically have two pairs of chelae (claws), while dendrobranchiates have three. A third group, the Stenopodidea, contains around 70 species and differs from the other groups in that the third pair of legs is greatly enlarged.

The cladogram below shows Caridea's relationships to other relatives within Decapoda, from analysis by Wolfe et al., 2019.

The below cladogram shows the internal relationships of eight selected families within Caridea, with the Atyidae (freshwater shrimp) being the most basal:

! Atyoidea

| 120px|Atya gabonensis Atya gabonensis

| valign=top | Contains one family, Atyidae, with 42 genera.

! Campylonotoidea

| valign=top | 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. Using molecular phylogenetics, Bracken et al. proposed that Campylonotoidea may be closer to Atyoidea (above).

! Crangonoidea

| 120px|Crangon crangon Crangon crangon

| valign=top | Contains two families: including the family Crangonidae.

! Galatheacaridoidea

| valign=top | 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. Molecular phylogenetic analyses has indicated that Galatheacaris abyssalis is the larval stage of Eugonatonotus.

! Nematocarcinoidea

| 120px|Rhynchocinetes durbanensis Rhynchocinetes durbanensis

| valign=top | Contains four families. They share the presence of strap-like epipods on at least the first three pairs of pereiopods, and a blunt molar process. One of the families, Rhynchocinetidae, are a group of small, reclusive red-and-white shrimp. This family typically has an upward-hinged foldable rostrum, Pictured is Rhynchocinetes durbanensis.

! Oplophoroidea

| 120px|Hymenodora glacialis Hymenodora glacialis

| valign=top | There is only one family, Oplophoridae, of this pelagic shrimp, which contains 12 genera.

! Processoidea

| valign=top | Contains a single family comprising 65 species in 5 genera.

! Psalidopodoidea

| 120px|Psalidopus huxleyi Psalidopus huxleyi

| valign=top | Contains a single family comprising three species, one in the western Atlantic Ocean, and two in the Indo-Pacific.

! Stylodactyloidea

| valign=top | Contains a single family made up of five genera. A number of extinct genera cannot be placed in any superfamily: