''Eurypanopeus depressus'', the flatback mud crab or depressed mud crab, is a true crab belonging to the infraorder Brachyura and the family Panopeidae. It is native to the western Atlantic Ocean and is often found in estuaries and lagoons, commonly living in close association with oysters.

Description

The flatback mud crab is a small species of crab up to long with a noticeably flattened, oval

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

, with four blunt teeth on either side. In colour, this crab is dark olive brown or olive grey, often somewhat mottled, with dark brown limbs. One chela (claw) is much bigger than the other and the underside of the body and the limbs are a pale colour.

Distribution and habitat

The flatback mud crab is found in the sub-tropical and temperate waters of the western Atlantic Ocean. Its range extends from Massachusetts to Florida and Texas, the Caribbean Sea, Bermuda, the Dutch West Indies and Uruguay. It occurs in the intertidal zone and the shallow sub-littoral zone, down to depths of about . It is tolerant of water of low salinities and occurs in estuaries. It is common in the

Indian River Lagoon The Indian River Lagoon is a grouping of three lagoons: the Mosquito Lagoon, the Banana River, and the Indian River, on the Atlantic Coast of Florida; one of the most biodiverse estuaries in the Northern Hemisphere and is home to more than 4,300 ...

. It is generally associated with oysters, hiding between them and inside their valves.

Ecology

This crab has an omnivorous diet which includes

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

, oyster spats, polychaete worms, sponges,

amphipod Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descr ...

s and other small crustaceans. When fully submerged it moves about on the substrate but when exposed by the retreating tide it conceals itself, being particularly associated with beds of the eastern oyster (''Crassostrea virginica''). It cannot withstand desiccation so it chooses moist places in which to hide. It shares its habitat with the black-fingered mud crab (''Panopeus herbstii''). The flatback mud crab is sometimes

parasitised Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

by '' Loxothylacus panopaei'', a species of parasitic

barnacle A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in eros ...

that develops inside a

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman * Michel Host ...

crab, extruding a brood sac that the crab then carries under its abdomen and treats as it would its own eggs.

References

{{Taxonbar, from=Q6498741 Xanthoidea Crustaceans of the Atlantic Ocean Crustaceans described in 1869