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 Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s within the class

Malacostraca Malacostraca is the second largest of the six classes of pancrustaceans behind insects, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crab ...

, 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 ...

crayfish Crayfish are freshwater crustaceans belonging to the infraorder Astacidea, which also contains lobsters. Taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea. They breathe through feather-like gills. Some spe ...

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

, and

prawns Prawn is a common name for small aquatic crustaceans with an exoskeleton and ten legs (members of the order of decapods), some of which are edible. The term ''prawn''Mortenson, Philip B (2010''This is not a weasel: a close look at nature's most ...

. Most decapods are

scavenger Scavengers are animals that consume Corpse decomposition, dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a he ...

s. 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 crab Hermit crabs are anomuran Decapoda, decapod crustaceans of the superfamily (taxonomy), superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. There are over 800 species of hermit c ...

s, king crabs,

porcelain crab Porcelain crabs are decapod crustaceans in the widespread family Porcellanidae, which superficially resemble true crabs. They have flattened bodies as an adaptation for living in rock crevices. They are delicate, readily losing limbs when attacke ...

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 Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

, ', "ten", and , '' -pod'', "foot") implies, ten of these appendages are considered legs. They are the

pereiopod The anatomy of a decapod consists of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment – often called a somite – may possess one pair of appendages, although in various groups these m ...

s, 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

maxilliped An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...

s 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

pleopod The anatomy of a decapod consists of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment – often called a somite – may possess one pair of appendages, although in various groups these m ...

s. 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 The telson () is the hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segm ...

, form the tail fan. Haeckel Decapoda

Evolution

A 2019

molecular clock The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleot ...

analysis suggested decapods originated in the Late Ordovician around 455 million years ago, with the

Dendrobranchiata Dendrobranchiata is a suborder of Decapoda, decapods, commonly known as prawns. There are 540 extant species in seven families, and a fossil record extending back to the Devonian. They differ from related animals, such as Caridea and Stenopodidea ...

(prawns) being the first group to diverge. The remaining group, called Pleocyemata, then diverged between the swimming

groupings and the crawling/walking group called Reptantia, consisting of

lobsters Lobsters are malacostracans decapod crustaceans of the family Nephropidae or its synonym Homaridae. They have long bodies with muscular tails and live in crevices or burrows on the sea floor. Three of their five pairs of legs have claws, in ...

and

crabs Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek), which typically have a very short projecting tail-like abdomen, usually hidden entirely under the thorax. Their exoskeleton is often thickened and ha ...

. 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 Devonian ( ) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at million years ago ( Ma), to the beginning of the succeeding ...

. 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:

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

Bate, 1888 ** Penaeoidea Rafinesque, 1815 ** Sergestoidea Dana, 1852 *Suborder Pleocyemata Burkenroad, 1963 **Infraorder Stenopodidea Bate, 1888 **Infraorder

Caridea 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 sh ...

Dana, 1852 *** Procaridoidea Chace & Manning, 1972 *** Galatheacaridoidea Vereshchaka, 1997 ***

Pasiphaeoidea Pasiphaeidae is a family (biology), family of Caridea, shrimp. It is the only family in the Taxonomic rank, superfamily Pasiphaeoidea and contains seven extant genera: *''Alainopasiphaea'' Hayashi, 1999 *''Eupasiphae'' Wood-Mason, 1893 *''Glyphus ...

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 ''Physetocaris'' is a monotypic genus of caridean shrimp, containing a single species, ''Physetocaris microphthalma''. Systematics ''Physetocaris microphthalma'' was previously placed in its own family (Physetocarididae) and superfamily (Physe ...

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 The Glypheoidea (containing the glypheoid lobsters), is a group of lobster-like Decapoda, decapod crustaceans which forms an important part of fossil faunas, such as the Solnhofen limestone. These fossils included taxa such as ''Glyphea'' (from wh ...

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 Hippoidea is a superfamily of decapod crustaceans known as mole crabs or sand crabs. Ecology Hippoids are adapted to burrowing into sandy beaches, a habit they share with raninid crabs, and the parallel evolution of the two groups is strikin ...

Latreille, 1825a *** Chirostyloidea Ortmann, 1892 *** Lomisoidea Bouvier, 1895 ***

Paguroidea Hermit crabs are anomuran decapod crustaceans of the superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. There are over 800 species of hermit crab, most of which possess an asy ...

Latreille, 1802 **Infraorder Brachyura Linnaeus, 1758 ***Section

Dromiacea Dromiacea is a group of crabs, ranked as a section. It contains 240 extant and nearly 300 extinct species. Dromiacea is the most basal grouping of Brachyura crabs, diverging the earliest in the evolutionary history, around the Late Triassic o ...

De Haan, 1833 **** Dromioidea De Haan, 1833 ****

Homolodromioidea Homolodromiidae is a family of crabs, the only family in the superfamily Homolodromioidea. In contrast to other crabs, including the closely related Homolidae, there is no strong ''linea homolica'' along which the exoskeleton breaks open during ec ...

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 Eubrachyura is a group of decapod crustaceans ( ranked as a "section") comprising the more derived crabs. It is divided into two subsections, based on the position of the genital openings in the two sexes. In the Heterotremata, the openings are o ...

de Saint Laurent, 1980 ****Subsection

Heterotremata Heterotremata is a clade of crabs, comprising those crabs in which the genital openings are on the sternum in females, but on the legs in males. It comprises 68 families in 28 superfamilies. Evolution Heterotremata is the sister group to Thora ...

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 Leucosioidea is a superfamily of 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 ...

Samouelle, 1819 *****

Majoidea The Majoidea are a Superfamily (taxonomy), superfamily of crabs which includes the various spider crabs. Taxonomy In "''A classification of living and fossil genera of decapod crustaceans''" De Grave and colleagues divided Majoidea into six fam ...

Samouelle, 1819 *****

Orithyioidea ''Orithyia sinica'', sometimes called tiger crab or the tiger face crab, is a "singularly unusual" species of crab, whose characteristics warrant its separation into a separate genus, family and even superfamily, having previously been included ...

Dana, 1852c *****

Palicoidea Palicoidea is a superfamily of crabs, comprising the two families Crossotonotidae and Palicidae. Together, they contain 13 genera, including two genera in the Palicidae known only from fossils. The two families were previously treated as two ...

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 The Ocypodoidea, or ocypoid crabs, are a superfamily of 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#Arthro ...

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