Hippoidea is a superfamily of decapod

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

s known as sand crabs or mole crabs.

Ecology

Hippoids are

adapted In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...

to burrowing into

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class o ...

beach A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc sh ...

es, a habit they share with raninid crabs, and the

parallel evolution Parallel evolution is the similar development of a trait in distinct species that are not closely related, but share a similar original trait in response to similar evolutionary pressure.Zhang, J. and Kumar, S. 1997Detection of convergent and paral ...

of the two groups is striking. In the family Hippidae, the body is almost ovoid, the first pereiopods have no

claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or tarsus ...

s, and the

telson The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on accou ...

is long, none of which are seen in related groups. Unlike most other

decapods The Decapoda or decapods (literally "ten-footed") are an order (biology), order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, Caridea, shrimp and Dendrobranchiata, prawns. Most ...

, sand crabs cannot walk; instead, they use their legs to dig into the sand. Members of the family Hippidae beat their uropods to swim. Apart from the polar regions, hippoids can be found on beaches throughout the world. Larvae of one species have also been found in Antarctic waters, despite the lack of suitable sandy beaches in the Antarctic.

Classification

Alongside

hermit crab 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 as ...

s and allies (Paguroidea),

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, alongsi ...

s and allies (

Galatheoidea The Galatheoidea are a superfamily of decapod crustaceans comprising the porcelain crabs and some squat lobsters. Squat lobsters within the three families of the superfamily Chirostyloidea are not closely related to the squat lobsters within th ...

) and the

hairy stone crab The hairy stone crab (''Lomis hirta'') is a crab-like crustacean that lives in the littoral zone of southern Australia from Bunbury, Western Australia, to the Bass Strait. It is the only species in its family (biology), family. It is wide, slow- ...

(''Lomis hirta'', Lomisoidea), Hippoidea is one of the four groups that make up the infraorder

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 grou ...

. Of the four, Hippoidea is thought to be the most basal, with the other three groups being more closely related to each other than to Hippoidea. The

fossil record A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

of sand crabs is sparse, but extends back to the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

period. Sand crabs are placed in three families (exclusively fossil taxa are marked †): ; Albuneidae Stimpson, 1858 *''

Albunea The Tiburtine Sibyl or Albunea was a Roman sibyl, whose seat was the ancient Etruscan town of Tibur (modern Tivoli). The mythic meeting of Cæsar Augustus with the Sibyl, of whom he inquired whether he should be worshiped as a god, was ofte ...

'' Weber, 1795 *'' Austrolepidopa'' Efford & Haig, 1968 *'' Harryhausenia'' Boyko, 2004 † *'' Italialbunea'' Boyko, 2002 † *'' Lepidopa'' Stimpson, 1858 *'' Leucolepidopa'' Efford, 1969 *'' Paralbunea'' Serène, 1977 *'' Paraleucolepidopa'' Calado, 1996 *'' Praealbunea'' Fraaije, 2002 † *'' Squillalbunea'' Boyko, 2002 *'' Stemonopa'' Efford & Haig, 1968 *'' Zygopa'' Holthuis, 1961 ; Blepharipodidae Boyko, 2002 *'' Blepharipoda'' Randall, 1840 *'' Lophomastix'' Benedict, 1904 ; Hippidae Latreille, 1825 *'' Emerita'' Scopoli, 1777 *''

Hippa ''Hippa'' is a genus of decapod crustaceans in the family Hippidae, containing the following species: *''Hippa adactyla ''Hippa adactyla'' is a species of small, sand-burrowing Decapoda, decapod crustacean found living along the coasts of I ...

'' Fabricius, 1787 *'' Mastigochirus'' Miers, 1878

References

External links

* {{Taxonbar, from=Q1145440 Anomura Extant Maastrichtian first appearances Arthropod superfamilies