Crab

Brachyuracrabstrue crabtrue crabsKaniblue crabsBox crabbrachyuranbrachyuran crabbrachyuran crabs
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) (βραχύς = short, οὐρά / οura = tail ), usually entirely hidden under the thorax.wikipedia
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Crustacean

Crustaceacrustaceanscarcinology
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) (βραχύς = short, οὐρά / οura = tail ), usually entirely hidden under the thorax.
Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such familiar animals as crabs, lobsters, crayfish, shrimps, prawns, krill, woodlice, and barnacles.

Decapoda

decapoddecapodsdecapod crustaceans
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) (βραχύς = short, οὐρά / οura = tail ), usually entirely hidden under the thorax.
The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns, and shrimp.

King crab

LithodidaeKinglithodid
Many other animals with similar names – such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs, and crab lice – are not true crabs.
King crabs are a taxon of crab-like decapod crustaceans chiefly found in cold seas.

Porcelain crab

Porcellanidaeporcelain
Many other animals with similar names – such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs, and crab lice – are not true crabs.
Porcelain crabs are decapod crustaceans in the widespread family Porcellanidae, which superficially resemble true crabs.

Horseshoe crab

horseshoe crabsLimulidaeLimuloidea
Many other animals with similar names – such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs, and crab lice – are not true crabs.
Their popular name is a misnomer, for they are not true crabs.

Pea crab

Pinnotheres pisum
Crabs vary in size from the pea crab, a few millimetres wide, to the Japanese spider crab, with a leg span of up to 4 m.
The pea crab, Pinnotheres pisum, is a small crab in the family Pinnotheridae that lives as a parasite in oysters, clams, mussels, and other species of bivalves.

Exoskeleton

shellshellsexoskeletal
Crabs are generally covered with a thick exoskeleton, composed primarily of highly mineralized chitin, and armed with a single pair of chelae (claws).
Examples of animals with exoskeletons include insects such as grasshoppers and cockroaches, and crustaceans such as crabs and lobsters, as well as the shells of certain sponges and the various groups of shelled molluscs, including those of snails, clams, tusk shells, chitons and nautilus.

Japanese spider crab

Macrocheiradeep sea crabsgiant crabs
Crabs vary in size from the pea crab, a few millimetres wide, to the Japanese spider crab, with a leg span of up to 4 m.
The Japanese spider crab, or Macrocheira kaempferi, is a species of marine crab that lives in the waters around Japan.

Fiddler crab

Ucafiddler crabsCrab
Males often have larger claws, a tendency which is particularly pronounced in the fiddler crabs of the genus Uca (Ocypodidae).
A fiddler crab, sometimes known as a calling crab, may be any of approximately 100 species of semi-terrestrial marine crabs which make up the genus Uca.

Ocypodidae

Males often have larger claws, a tendency which is particularly pronounced in the fiddler crabs of the genus Uca (Ocypodidae).
The Ocypodidae are a family of semiterrestrial crabs that includes the ghost crabs and fiddler crabs.

Freshwater crab

freshwater crabscrabsfreshwater
About 850 species are saltwater crabs, brackish water crabs, freshwater crabs, terrestrial crabs or semi-terrestrial crabs.
Members of the family Aeglidae and Clibanarius fonticola are also restricted to fresh water, but these "crab-like" crustaceans are members of the infraorder Anomura (true crabs are Brachyura).

Terrestrial crab

land crabland crabsterrestrial
About 850 species are saltwater crabs, brackish water crabs, freshwater crabs, terrestrial crabs or semi-terrestrial crabs. Crabs are found in all of the world's oceans, while many crabs live in fresh water and on land, particularly in tropical regions.
A number of lineages of crabs have evolved to live predominantly on land.

Predation

predatorypredatorprey
The radiation of crabs in the Cretaceous and afterward may be linked either to the break-up of Gondwana or to the concurrent radiation of bony fish, crabs' main predators.
Among crustaceans, lobsters, crabs, shrimps and barnacles are predators, and in turn crustaceans are preyed on by nearly all cephalopods (including octopuses, squid and cuttlefish).

Raninidae

raninidraninids
However, some crabs walk forwards or backwards, including raninids, Libinia emarginata and Mictyris platycheles.
Raninidae is a family of unusual crabs, sometimes known as "frog crabs", on account of their frog-like appearance.

Portunidae

swimming crabPortunitesswimming crabs
Some crabs, notably the Portunidae and Matutidae, are also capable of swimming, the Portunidae especially so as their last pair of walking legs is flattened into swimming paddles.
Portunidae is a family of crabs which contains the swimming crabs.

Libinia emarginata

portly spider crabCommon Spider Crabspider crab
However, some crabs walk forwards or backwards, including raninids, Libinia emarginata and Mictyris platycheles.
Libinia emarginata, the portly spider crab, common spider crab or nine-spined spider crab, is a species of stenohaline crab that lives on the Atlantic coast of North America.

Matutidae

matutid
Some crabs, notably the Portunidae and Matutidae, are also capable of swimming, the Portunidae especially so as their last pair of walking legs is flattened into swimming paddles.
Matutidae is a family of crabs, sometimes called moon crabs, adapted for swimming or digging.

Mictyris platycheles

However, some crabs walk forwards or backwards, including raninids, Libinia emarginata and Mictyris platycheles.
Mictyris platycheles is a species of crab found on mudflats on the east coast of Australia from Tasmania and Victoria to Queensland.

Crustacean larva

larvaezoeanauplius
When development is complete, the female releases the newly hatched larvae into the water, where they are part of the plankton.
Any organs which are absent from the adults do not generally appear in the larvae, although there are a few exceptions, such as the vestige of the fourth pereiopod in the larvae of Lucifer, and some pleopods in certain Anomura and crabs.

Callinectes sapidus

blue crabblue crabsAtlantic blue crab
Other commercially important taxa include Portunus pelagicus, several species in the genus Chionoecetes, the blue crab (Callinectes sapidus), Charybdis spp., Cancer pagurus, the Dungeness crab (Metacarcinus magister), and Scylla serrata, each of which yields more than 20,000 tonnes annually.
Callinectes sapidus (from the Greek calli- = "beautiful", nectes = "swimmer", and Latin sapidus = "savory"), the Blue Crab, Atlantic Blue Crab, or regionally as the Chesapeake blue crab, is a species of crab native to the waters of the western Atlantic Ocean and the Gulf of Mexico, and introduced internationally.

Hermit crab

hermit crabsPaguroideahermit-crabbed
Many other animals with similar names – such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs, and crab lice – are not true crabs.

Portunus armatus

Portunus pelagicusblue crabblue swimmer crabs
Other commercially important taxa include Portunus pelagicus, several species in the genus Chionoecetes, the blue crab (Callinectes sapidus), Charybdis spp., Cancer pagurus, the Dungeness crab (Metacarcinus magister), and Scylla serrata, each of which yields more than 20,000 tonnes annually.
Portunus armatus (formerly Portunus pelagicus ), also known as the flower crab, blue crab, blue swimmer crab, blue manna crab or sand crab, rajungan in Indonesian, and alimasag in Tagalog, Kapampangan, and Pangasinan, is a large crab found in the intertidal estuaries around most of Australia and east to New Caledonia.

Dungeness crab

Metacarcinus magisterCancer magistercrab
Other commercially important taxa include Portunus pelagicus, several species in the genus Chionoecetes, the blue crab (Callinectes sapidus), Charybdis spp., Cancer pagurus, the Dungeness crab (Metacarcinus magister), and Scylla serrata, each of which yields more than 20,000 tonnes annually.
The Dungeness crab, Metacarcinus magister (the naming convention recognised by WoRMS) or Cancer magister (the naming convention recognised by ITIS), is a species of crab that inhabits eelgrass beds and water bottoms on the west coast of North America.

Chionoecetes

snow crabTanner crabMatsuba crab
Other commercially important taxa include Portunus pelagicus, several species in the genus Chionoecetes, the blue crab (Callinectes sapidus), Charybdis spp., Cancer pagurus, the Dungeness crab (Metacarcinus magister), and Scylla serrata, each of which yields more than 20,000 tonnes annually.
Chionoecetes is a genus of crabs that live in the northern Pacific and Atlantic Oceans.

Portunus trituberculatus

horse crabblue crabcrab
One species, Portunus trituberculatus, accounts for one-fifth of that total.
Portunus trituberculatus, the gazami crab, Japanese blue crab or horse crab, is the most widely fished species of crab in the world.