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 decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...

s known as sand crabs or mole crabs.

Ecology

Hippoids are adapted 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 ...

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 s ...

es, a habit they share with raninid crabs, and the parallel evolution 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 o ...

, 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 variou ...

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 acco ...

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

; 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 c ...

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 zones or polar zones, of Earth are the regions of the planet that surround its geographical poles (the North and South Poles), lying within the polar circles. These high latitudes are dominated by flo ...

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 as ...

s and allies (Paguroidea), squat lobsters and allies ( Galatheoidea) and the hairy stone crab (''Lomis hirta'', Lomisoidea), Hippoidea is one of the four groups that make up the infraorder Anomura. 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 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 and Oligocene The ...

Stimpson, 1858 *'' Albunea'' 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 Blepharipodidae is a family of sand crabs (Hippoidea), comprising the two genera '' Blepharipoda'' and '' Lophomastix''. They are distinguished from the other families in the superfamily Hippoidea by the form of the gills, which are trichobranchi ...

Boyko, 2002 *'' Blepharipoda'' Randall, 1840 *'' Lophomastix'' Benedict, 1904 ;

Latreille, 1825 *'' Emerita'' Scopoli, 1777 *'' Hippa'' Fabricius, 1787 *'' Mastigochirus'' Miers, 1878

References

External links

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