Heterotremata
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Heterotremata is a
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 ...
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 hidden entirely under the Thorax (arthropo ...
s, comprising those crabs in which the genital openings are on the
sternum The sternum (: sternums or sterna) or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major bl ...
in females, but on the legs in males. It comprises 68 families in 28 superfamilies.


Evolution

Heterotremata is the
sister group 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 Thoracotremata within the clade Eubrachyura, having diverged during the
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 ...
period. Eubrachyura itself is a subset of the larger clade Brachyura, which consists of all "true crabs". A summary of the high-level internal relationships within Brachyura can be shown in 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: The internal relationships within Heterotremata are less certain, with many of the superfamilies found to be invalid. The proposed
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 is from analysis by Tsang ''et al'', 2014:


Superfamilies

* Aethroidea * Bellioidea * Bythograeoidea * Calappoidea * Cancroidea * Carpilioidea * Cheiragonoidea * Corystoidea * Dairoidea * Dorippoidea * Eriphioidea * Gecarcinucoidea * Goneplacoidea * Hexapodoidea *
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 ...
*
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 ...
*
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 ...
*
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 ...
* Parthenopoidea * Pilumnoidea * Portunoidea * Potamoidea * Pseudothelphusoidea * Pseudozioidea * Retroplumoidea * Trapezioidea * Trichodactyloidea * Xanthoidea However, recent studies have found the following superfamilies and
families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...
to not be
monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...
, but rather
paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
or
polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...
: *The superfamilies Calappoidea, Eriphioidea, and Goneplacoidea are polyphyletic *The superfamily Potamoidea is paraphyletic with respect to Gecarcinucoidea, which is resolved by placing
Gecarcinucidae The Gecarcinucidae are a family of true freshwater crabs. They are found throughout South Asia, Southeast Asia and New Guinea, with a single genus found in Australia. Taxonomy The family Parathelphusidae is now demoted to the rank of subfamily ...
within Potamoidea *The
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 ...
families Epialtidae, Mithracidae and
Majidae Majidae is a family (biology), family of crabs, comprising around 200 Ocean, marine species inside 52 genera, with a carapace that is longer than it is broad, and which forms a point at the front. The arthropod leg, legs can be very long in some ...
are polyphyletic with respect to each other *The Xanthoidea family
Xanthidae Xanthidae is a family (biology), family of crabs known as gorilla crabs, mud crabs, pebble crabs or rubble crabs. Xanthid crabs are often brightly coloured and are highly poisonous, containing toxins which are not destroyed by cooking and for wh ...
is paraphyletic with respect to
Panopeidae The Panopeidae are a family (biology), family containing 26 genera of morphologically similar crabs, often known as "mud crabs". Their center of diversity, centers of diversity are the Atlantic Ocean and eastern Pacific Ocean. Distribution Most ...


References


External links

* {{Taxonbar, from=Q902172 Crabs