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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 .
A number of lineages of crabs have evolved to live predominantly on land. Examples of terrestrial crabs are found in the families Gecarcinidae and Gecarcinucidae, as well as in selected genera from other families, such as Sesarma, [1] although the term "land crab" is often used to mean solely the family Gecarcinidae. [2]
Horseshoe crabs have been described as "living fossils", having changed little since they first appeared in the Triassic. Only four species of horseshoe crab are extant today. Most are marine, though the mangrove horseshoe crab is often found in brackish water. Additionally, certain extinct species transitioned to living in freshwater.
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.
They are known to be cannibalistic, and consume smaller crabs, small reptiles and amphibians, molluscs, fish, and insects if they can catch them. While juvenile and adult crabs spend most of their time on dry land, the females must return to the ocean to release their eggs. The eggs hatch into microscopic larvae, and later on develop into young ...
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 crabs human see or eat are usually only six or so inches across their shells. An aerial image taken in the UK captured a massive crab, and is now garnering a lot of attention online.
The coconut crab (Birgus latro) is a terrestrial species of giant hermit crab, and is also known as the robber crab or palm thief. It is the largest terrestrial arthropod known, with a weight of up to 4.1 kg (9 lb). The distance from the tip of one leg to the tip of another can be as wide as 1 m (3 ft 3 in).