Hippoidea is a

superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...

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 ...

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 of s ...

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 shel ...

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 Hippidae is a family of decapod crustaceans, currently known by the English name as either mole crab or sand crab, and by an earlier English name as sand bug. They are closely related to the family Albuneidae, with which they are usually joined ...

, the body is almost

ovoid An oval () is a closed curve in a plane which resembles the outline of an egg. The term is not very specific, but in some areas (projective geometry, technical drawing, etc.) it is given a more precise definition, which may include either one or ...

, the first

pereiopod The decapod (crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various g ...

s 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 of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, shrimp and prawns. Most decapods are scavengers. The order is estim ...

, sand crabs cannot

walk Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined by an 'inverted pendulum' gait in which the body vaults ov ...

; instead, they use their

legs A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element ...

to dig into the sand. Members of the family

beat their

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 to swim. Apart from the

polar region The polar regions, also called the frigid geographical zone, zones or polar zones, of Earth are the regions of the planet that surround its geographical poles (the North Pole, North and South Poles), lying within the polar circles. These high l ...

s, 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 a ...

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, alongside ...

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 the ...

) 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. It is wide, slow-moving, and covere ...

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

Anomura Anomura (sometimes Anomala) is a group of Decapoda, 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 ...

. 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 in ...

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 th ...

period. Sand crabs are placed in three families (exclusively fossil taxa are marked †): ;

Albuneidae Albuneidae is a little-known family of specialized burrowing sand crabs. There are 50 extant species as well as nine fossil species that have been described. Fossil specimens have been described from the Cretaceous, Miocene The Miocene ( ) i ...

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 ;

Latreille, 1825 *'' Emerita'' Scopoli, 1777 *''

Hippa ''Hippa'' is a genus of decapod crustaceans in the family Hippidae, containing the following species: *''Hippa adactyla'' Fabricius, 1787 *''Hippa admirabilis'' Thallwitz, 1892 *''Hippa alcimede'' de Man, 1902 *''Hippa australis'' Hale, 1927 ...

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

References

External links

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