The Decapoda or decapods, from Ancient Greek δεκάς ( dekás), meaning "ten", and πούς ( poús), meaning "foot", is a large order of within the class Malacostraca, and includes , , crayfish, Caridea, and Dendrobranchiata. Most decapods are . The order is estimated to contain nearly 15,000 extant species in around 2,700 genera, with around 3,300 fossil species.
Anatomy
Decapods can have as many as 38 appendages,
arranged in one pair per body segment. As the name Decapoda (from the
Greek language δέκα]],
deca-]], "ten", and πούς]] / ποδός,
-pod, "foot") implies, ten of these appendages are considered legs. They are the
, 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
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
. There is one final pair called
, which, with the
telson, form the tail fan.
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 and
Cretaceous periods, which coincides with the rise and spread of modern
coral reefs, 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 below shows the internal relationships of Decapoda, from analysis by Wolfe et al. (2019).[
]
In the cladogram above, the clade Glypheidea is excluded due to lack of sufficient DNA evidence, but is likely the sister taxon to Polychelida, within Reptantia.[
]
Classification
Classification within the order Decapoda depends on the structure of the and legs, and the way in which the 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".
This classification to the level of superfamilies follows De Grave et al.
Order Decapoda Latreille, 1802
-
Suborder Dendrobranchiata Bate, 1888
-
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
-
Infraorder Glypheidea Winckler, 1882
-
Infraorder Axiidea de Saint Laurent, 1979b
-
Infraorder Gebiidea de Saint Laurent, 1979
-
Infraorder Achelata Scholtz & Richter, 1995
-
Infraorder Polychelida Scholtz & Richter, 1995
-
Infraorder Anomura MacLeay, 1838
-
Infraorder Brachyura Linnaeus, 1758
-
Section Dromiacea De Haan, 1833
-
Section Raninoida 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
See also
-
List of Atlantic decapod species
-
Phylogeny of Malacostraca
External links
-
Decapod Crustacea "Tree of Life" page at the Natural History Museum of Los Angeles County
