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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 (). [1] [2] Each segment may possess one pair of appendages, although in various groups these may be reduced or missing.
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 .
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]
A hermit crab emerges from its shell, Coenobita perlatus Outside its shell, the soft, curved abdomen of hermit crabs, such as Pagurus bernhardus, is vulnerable. Hermit crab species range in size and shape, from species only a few millimeters long to Coenobita brevimanus (Indos Crab), which can approach the size of a coconut and live 12–70 years.
The molted carapace of a lady crab from Long Beach, New York. In crustaceans, the carapace functions as a protective cover over the cephalothorax (i.e., the fused head and thorax, as distinct from the abdomen behind). Where it projects forward beyond the eyes, this projection is called a rostrum.
The aerial shot enables viewers to see the full body of the crab, including its pinchers and legs. It's estimated that the beast measures 50 feet long. Quinton Winter, who runs a website devoted ...
Horseshoe crabs are arthropods of the family Limulidae and the only surviving xiphosurans. Despite their name, they are not true crabs or even crustaceans; they are chelicerates, more closely related to arachnids like spiders, ticks, and scorpions. The body of a horseshoe crab is divided into three main parts: the cephalothorax, abdomen, and ...
Carcinisation (American English: carcinization) is a form of convergent evolution in which non-crab crustaceans evolve a crab-like body plan. The term was introduced into evolutionary biology by Lancelot Alexander Borradaile , who described it as "the many attempts of Nature to evolve a crab".