The Decapoda or decapods, from

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

δεκάς (''dekás''), meaning "ten", and πούς (''poús''), meaning "foot", is a large order of crustaceans within the class Malacostraca, and includes

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

lobster Lobsters are Malacostraca, malacostracans Decapoda, decapod crustaceans of the family (biology), family Nephropidae or its Synonym (taxonomy), synonym Homaridae. They have long bodies with muscular tails and live in crevices or burrows on th ...

s, crayfish, shrimp, and prawns. Most decapods are scavengers. The order is estimated to contain nearly 15,000 extant species in around 2,700 genera, with around 3,300 fossil species. Nearly half of these species are crabs, with the shrimp (about 3,000 species) and

Anomura Anomura (sometimes Anomala) is a group of decapod crustaceans, including hermit crabs and others. Although the names of many anomurans include the word ''crab'', all true crabs are in the sister group to the Anomura, the Brachyura (the two groups ...

including hermit crabs, king crabs, porcelain crabs,

squat lobster Squat lobsters are dorsoventrally flattened crustaceans with long tails held curled beneath the cephalothorax. They are found in the two superfamilies Galatheoidea and Chirostyloidea, which form part of the decapod infraorder Anomura, alongs ...

s (about 2500 species) making up the bulk of the remainder. The earliest fossils of the group date to the

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

Anatomy

Decapods can have as many as 38 appendages, arranged in one pair per body segment. As the name Decapoda (from the Greek , ', "ten", and , '' -pod'', "foot") implies, ten of these appendages are considered legs. They are the pereiopods, found on the last five thoracic segments. In many decapods, one pair of these "legs" has enlarged pincers, called chelae, with the legs being called chelipeds. In front of the pereiopods are three pairs of maxillipeds that function as feeding appendages. The head has five pairs of appendages, including mouthparts, antennae, and antennules. There are five more pairs of appendages on the abdomen. They are called pleopods. There is one final pair called

uropod Uropods are posterior appendages found on a wide variety of crustaceans. They typically have functions in locomotion. Definition Uropods are often defined as the appendages of the last body segment of a crustacean. An alternative definition sugge ...

s, which, with the telson, form the tail fan. Haeckel Decapoda

Evolution

A 2019 molecular clock analysis suggested decapods originated in the Late Ordovician around 455 million years ago, with the Dendrobranchiata (prawns) being the first group to diverge. The remaining group, called Pleocyemata, then diverged between the swimming shrimp groupings and the crawling/walking group called Reptantia, consisting of lobsters and crabs. High species diversification can be traced to the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

and

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

periods, which coincides with the rise and spread of modern

coral reefs A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. ...

, a key habitat for the decapods. Despite the inferred early origin, the oldest fossils of the group such as '' Palaeopalaemon'' only date to the Late Devonian. The

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

below shows the internal relationships of Decapoda, from analysis by Wolfe ''et al.'' (2019). In the cladogram above, the

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

Glypheidea is excluded due to lack of sufficient DNA evidence, but is likely the

sister clade In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to Polychelida, within Reptantia.

Classification

Classification within the order Decapoda depends on the structure of the

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

s and legs, and the way in which the

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e develop, giving rise to two suborders: Dendrobranchiata and Pleocyemata. The Dendrobranchiata consist of prawns, including many species colloquially referred to as "shrimp", such as the "white shrimp", '' Litopenaeus setiferus''. The Pleocyemata include the remaining groups, including "true shrimp". Those groups that usually walk rather than swim (Pleocyemata, excluding Stenopodidea and Caridea) form a clade called Reptantia. This classification to the level of superfamilies follows De Grave ''et al.'' Penaeus vannamei 01

Blue crab on market in Piraeus - Callinectes sapidus Rathbun 20020819-317

Order Decapoda Latreille, 1802 *Suborder Dendrobranchiata Bate, 1888 ** Penaeoidea Rafinesque, 1815 ** Sergestoidea Dana, 1852 *Suborder Pleocyemata Burkenroad, 1963 **Infraorder Stenopodidea Bate, 1888 **Infraorder Caridea Dana, 1852 *** Procaridoidea Chace & Manning, 1972 *** Galatheacaridoidea Vereshchaka, 1997 *** Pasiphaeoidea Dana, 1852 *** Oplophoroidea Dana, 1852 *** Atyoidea De Haan, 1849 *** Bresilioidea Calman, 1896 *** Nematocarcinoidea Smith, 1884 *** Psalidopodoidea Wood-....., 1874 *** Stylodactyloidea Bate, 1888 *** Campylonotoidea Sollaud, 1913 *** Palaemonoidea Rafinesque, 1815 *** Alpheoidea Rafinesque, 1815 *** Processoidea Ortmann, 1896 *** Pandaloidea Haworth, 1825 *** Physetocaridoidea Chace, 1940 *** Crangonoidea Haworth, 1825 **Infraorder Astacidea Latreille, 1802 *** Enoplometopoidea de Saint Laurent, 1988 *** Nephropoidea Dana, 1852 *** Astacoidea Latreille, 1802 *** Parastacoidea Huxley, 1879 **Infraorder Glypheidea Winckler, 1882 *** Glypheoidea Winckler, 1882 **Infraorder Axiidea de Saint Laurent, 1979b **Infraorder

Gebiidea Gebiidea is an infraorder of Decapoda, decapod crustaceans. Gebiidea and Axiidea are divergent infraoders of the former infraorder Thalassinidea. These infraorders have converged Ecology, ecologically and Morphology (biology), morphologically as ...

de Saint Laurent, 1979 **Infraorder Achelata Scholtz & Richter, 1995 **Infraorder Polychelida Scholtz & Richter, 1995 **Infraorder

MacLeay, 1838 *** Aegloidea Dana, 1852 *** Galatheoidea Samouelle, 1819 *** Hippoidea Latreille, 1825a *** Chirostyloidea Ortmann, 1892 *** Lomisoidea Bouvier, 1895 *** Paguroidea Latreille, 1802 **Infraorder Brachyura Linnaeus, 1758 ***Section Dromiacea De Haan, 1833 **** Dromioidea De Haan, 1833 **** Homolodromioidea Alcock, 1900 **** Homoloidea De Haan, 1839 ***Section

Raninoida Raninoida is a taxonomic section of the crabs, containing a single superfamily, Raninoidea. This group of crabs is unlike most, with the abdomen not being folded under the thorax. It comprises 46 extant species, and nearly 200 species known o ...

De Haan, 1839 ***Section Cyclodorippoida Ortmann, 1892 ***Section Eubrachyura de Saint Laurent, 1980 ****Subsection Heterotremata Guinot, 1977 ***** Aethroidea Dana, 1851 ***** Bellioidea Dana, 1852 ***** Bythograeoidea Williams, 1980 ***** Calappoidea De Haan, 1833 ***** Cancroidea Latreille, 1802 ***** Carpilioidea Ortmann, 1893 ***** Cheiragonoidea Ortmann, 1893 ***** Corystoidea Samouelle, 1819 ***** Dairoidea Serène, 1965 ***** Dorippoidea MacLeay, 1838 ***** Eriphioidea MacLeay, 1838 ***** Gecarcinucoidea Rathbun, 1904 ***** Goneplacoidea MacLeay, 1838 ***** Hexapodoidea Miers, 1886 ***** Leucosioidea Samouelle, 1819 ***** Majoidea Samouelle, 1819 ***** Orithyioidea Dana, 1852c ***** Palicoidea Bouvier, 1898 ***** Parthenopoidea MacLeay, ***** Pilumnoidea Samouelle, 1819 ***** Portunoidea Rafinesque, 1815 ***** Potamoidea Ortmann, 1896 ***** Pseudothelphusoidea Ortmann, 1893 ***** Pseudozioidea Alcock, 1898 ***** Retroplumoidea Gill, 1894 ***** Trapezioidea Miers, 1886 ***** Trichodactyloidea H. Milne-Edwards, 1853 ***** Xanthoidea MacLeay, 1838 ****Subsection Thoracotremata Guinot, 1977 ***** Cryptochiroidea Paul'son, 1875 ***** Grapsoidea MacLeay, 1838 ***** Ocypodoidea Rafinesque, 1815 ***** Pinnotheroidea De Haan, 1833

References

External links

*
Decapod Crustacea
"Tree of Life" page at the

Natural History Museum of Los Angeles County Nature is an inherent character or constitution, particularly of the ecosphere or the universe as a whole. In this general sense nature refers to the laws, elements and phenomena of the physical world, including life. Although humans are par ...

{{Authority control Crustacean orders Extant Devonian first appearances Taxa named by Pierre André Latreille

Anatomy

Evolution

Classification

See also

References

External links