CLASSIFICATION
CLASSIFICATION
Hermit crabs hide their soft abdomens in spiral shells cast off by sea snails or other mollusks. With two pairs of walking legs, the crabs drag their shells about with them. The other two pairs of walking legs are reduced and act as struts against the shell's inner wall. As the crab grows, it leaves its old shell and moves into a larger one.
Marine hermit crabs, family Paguridae, are common throughout the world, and land hermits, family Coenobitidae, are restricted to tropical and subtropical waters.
Most hermit crabs have long, soft abdomens that are spirally coiled. They occupy abandoned snail shells by thrusting the abdomen into the shell and holding onto it with the hooks on a pair of leglike organs. They do not kill the original owner of the shell, though they will fight other hermit crabs to determine occupancy of a shell. The hermit crab drags the shell behind as it walks about. As the crab grows larger, it seeks a larger shell.
Crabs inhabit a diversity of places and eat a variety of foods. Most crabs feed on small fish or worms or else scavenge along the shore or sea bottom. The tree-climbing robber crabhowever, feeds on coconut meat, which it obtains by drilling through the "eye" of the coconut with its powerful claws; the tree crab, Aratus pisonii, feeds to some extent on mangrove leaves. Most crabs, however, are scavengers, eating dead or decaying material. There is a commercial diet available for hermit crabs kept as pets, however hermit crabs seem partial to the roots of potted plants, and have been observed to dig up plants kept in their cages.
The crab's reproductive organs are situated near and just below the heart and open to the outside at the base of the last pair of walking legs in the male, and at the base of the middle pair of walking legs in the female. In most species, the female carries the eggs cemented to her undersides and protected by the flexed tail. The developing crabs pass through four stages, two of which (the nauplius and protozoea) occur while still in the egg. Most crabs hatch at the third stage, the zoea; a larva that has several long spines, a long narrow abdomen, and large fringed antennae. The fourth stage of development is the megalops. Crabs grow by shedding, or molting, their hard shells.
Hermit and other land crabs of tropical regions have adapted to life on dry land. However, they must retain some moisture because they do breathe with gills (with must be moist in order to function). In addition, in order to lay their eggs, they journey to the sea so that their young can spend their early lives in salt water. After reproducing, they return inland, and their young follow at a later time.
Crabs are an important food source. Some are canned and others are sold fresh to restaurants. In the United States three main kinds of crabs are caught for their meat. Blue crabs are caught commercially in open water by trawls or are removed from the mud with dredges. The "soft-shell crabs" served in restaurants are freshly molted adults whose carapaces have not hardened. A single king crab can provide as much as 5 pounds (2.3 kilograms) of meat. Various kinds of stone, rock, and sand crabs are gathered along coasts for food, but they are not commercially important. Some hermit crabs have symbiotic relationships with sponges. A hermit crab living in a cast-off snail shell may find that a sponge larva has moved in with it. The larva grows into a sponge whose unpleasant odor and taste discourage the crab's predators. The crab carries the sponge when it moves from place to place, and the sponge is able to filter water from the new sites. The back of another kind of crab is always covered with a growth of sponge, which serves as camouflage.
Compton's New Media, Inc., 1993
Scermino, Daniel. Hermit Crabs as Pets. Palmetto Publishing Co.