Hermit Crab, any crab of the Paguridae and Coenobitidae families (class Crustacea Decapoda order). These crabs are superfamily Paguroidea anomuran decapod crustaceans who adapted to occupy empty scavenged mollusc shells in order to protect their fragile exoskeletons. There are over 800 species of hermit crabs worldwide, and the majorities are ocean dwellers though people are likely most acquainted with the dozen semi-terrestrial species, called land hermit crabs, which are often kept as pets. There’s just one freshwater decapod crustacean, Clibanarius fonticola, which is native to Vanuatu.
Hermit crabs use empty snail shells (e.g., whelk or periwinkle) or other hollow objects as a protective shelter for partial body containment. They must occupy shelter that other organisms produce, or risk being defenseless against nature and its occupants. Their bodies lack a hard-guarded carapace; they are extremely vulnerable to predators without a shell.
Hermit crabs are omnivorous foragers, eating tiny mussels and shellfishes, pieces of dead creatures, and macroalgae. The solid relationship between recluse crabs and their havens has altogether affected their science. Just about 800 species convey portable havens (regularly calcified snail shells); this defensive versatility adds to the decent variety and a huge number of shellfish found in practically all marine conditions. On the front of their bodies, instead, hermit crabs have a hard exoskeleton but a soft tail on the other half, which they protect using other animals’ discarded shells, like whelks.
Hermit crabs, in distribution worldwide, occur in sandy or muddy-bottomed marine waters, and sometimes on land and in trees. The tip of the abdomen of the hermit crabs is adapted to clasp strongly onto the snail shell columella. The greatest numbers of hermit crabs are nocturnal. Hermit crabs have a curled tail with a hook that allows their bodies to suit inside these borrowed shells. Sometimes when a brand new shell turns up, hermit crabs will form a line, biggest to smallest, to determine which animal fits the new shell. The following smallest will take that crab’s hand-me-down home, and so on.
There are two antennae pairs, and five leg pairs. The first pair of legs is modified to form chelae, or the right one is usually larger pincers which are shaped to cover the entrance of the shell when the animal is within. The crab walks on its second and third pair of legs and uses their shorter fourth and fifth pairs to grip the snail shell’s central column. Hermit crabs vary in their mating habits. The Caribbean hermit crab, for example, lives in wetlands, but when it’s time to mate, will head for the seashore in huge masses.
Hermit crab species go fit as a fiddle, from species with a carapace just a couple of millimeters long to Coenobita brevimanus, which can live 12–70 years and can move toward the size of a coconut. The shell-less loner crab Birgus latro (coconut crab) is the world’s biggest earthbound invertebrate. Stomach extremities on the female convey the eggs, which are held there until they bring forth; the youthful go into the water as swimming hatchlings. The hatchlings in the long run transform into little crabs, at which time they should look for their own shells.
Hermit crabs are mostly seen as a “throwaway pet” that will live for just a few months, but if treated properly species such as Coenobita clypeatus have a 20-year lifespan and some have lived more than 32 years. As the crab grows and becomes too big for its shell, it has to locate and shift into one bigger one. The availability of suitable shells is often limited, so competition among hermit crabs for shells of the proper size and in good condition is intense.
A 2020 study within the Journal of Hazardous Materials found that around 570,000 hermit crabs die annually from getting caught in plastic debris on two tropical islands within the South Pacific. Hermit crabs are more closely associated with squat lobsters and porcelain crabs than they’re to true crabs (Brachyura). Pagurus pollicaris, an oversized decapod of the Atlantic coastal waters of North America, is reddish-brown and about 10 to 12 cm (4 to five inches) long. P. longicarpus, a far smaller decapod crustacean, occurs in shallow U.S. Atlantic coastal waters.
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