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Crabs vary in size from the pea crab, a few millimeters wide, to the Japanese spider crab, with a leg span up to 4 m (13 ft). [6] Several other groups of crustaceans with similar appearances – such as king crabs and porcelain crabs – are not true crabs, but have evolved features similar to true crabs through a process known as carcinisation .
More than 1,300 described species of freshwater crabs are known, out of a total of 6,700 species of crabs across all environments. [1] The total number of species of freshwater crabs, including undescribed species, is thought to be up to 65% higher, potentially up to 2,155 species, although most of the additional species are currently unknown to science. [1]
A shed carapace of a lady crab, part of the hard exoskeleton Body structure of a typical crustacean – krill. The body of a crustacean is composed of segments, which are grouped into three regions: the cephalon or head, [5] the pereon or thorax, [6] and the pleon or abdomen. [7]
The best way to identify them is through other characteristics, such as the five spines on either side of their eyes, with three in between them. Carcinus maenas is a common littoral crab. It is known by different names around the world. In the British Isles, it is generally referred to as the shore crab, or green shore crab.
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 groups together form the clade Meiura).
Several species of wild crab are the subject of crab fisheries around the coasts of the British Isles. The most important are the brown crab or edible crab, Cancer pagurus (29,193 t), various swimming crabs (3,180 t), the spider crab Maja brachydactyla (1,565 t), the shore crab or green crab Carcinus maenas (553 t) and the velvet crab Necora puber (193 t).
Between 2018 and 2021, there was an unexpected 92% decline in snow crab abundance, or about 10 billion crabs. The crabs had been plentiful in the years prior, puzzling scientists and crabbers alike.
The name "ghost crab" derives from their nocturnality and their generally pale coloration. [1] [2] They are also sometimes called sand crabs, though the name refers to various other crabs that do not belong to the subfamily. Characteristics of the subfamily include one claw being larger than the other, thick and elongated eyestalks, and a box ...