Caribbean hermit crab
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[Photo] Photograph of Coenobita clypeatus (Caribbean hermit crab) aka "tree-climbing crab", "purple pincher". Photo taken by user AbsolutDan http://en.wikipedia.org/wiki/User:AbsolutDan Date 2005-01-16

The Caribbean hermit crab (Coenobita clypeatus), also known as the tree crab, the tree-climbing crab, the soldier crab, and the purple pincher, is a species of land hermit crab commonly sold in the United States. The last of its common names is due to their distinctive purple claw. They can live to be over 30 years old (and over 40 years in exceptional cases).

The Caribbean hermit crab lives in the Arabian Sea, the Caribbean Sea, southern Florida, Venezuela, and the Bermuda Islands. They are omnivorous scavengers who live in colonies of 100 or more near the inland areas and who like to hide in caves or the roots of a tree. They prefer a relative humidity level between 70% and 78%, and a temperature of 24°C (75°F).

Physical description
Coenobita clypeatus is a member of the phylum Arthropoda and the class Malacostraca. They can be 17 mm in length. The color varies from a pale red to a dark brown or burgundy.

The eyestalks are round and white, with a black or brown stripe on the bottom. The eyes are oval in shape. The abdomen is short and fat. There are four walking legs, four tiny legs to hold the shell in place, a small pincher, a large purple pincher, and four antennae.

Although these hermit crabs live on land, they have gills, rather than lungs. The high relative humidity of their native environments, plus water carried in the shell, allows their modified gills to remain wet and to properly extract oxygen from the air.

Shell usage and shell fights
The land hermit crab uses a shell to protect its delicate body. The shell is sometimes that of a land snail when the crab is young, but usually that of a marine snail. Once deceased, the snail body decomposes and the empty shell eventually washes onto shore. The hermit crab can then occupy the shell. Larger shells are necessary as the crab grows, but that growth is quite slow.

Hermit crabs are very particular about their shells and shell switching is not uncommon as the crab searches for the perfect shell. A desired characteristic of that shell is an opening about the size of the large claw, plus about 2½???3 mm (1/10 in to 1/8 in) all around (more for larger crabs). When threatened, the crab withdraws into the shell and blocks the entrance with the large claw.

Fierce shell fights can occur if the shell supply is not adequate. The loser often dies since many hermit crabs will not release their grip on their shell until they are torn apart. The loss of limbs in shell fights is common, but may not result in death especially since the hermit crab can choose to drop (autotomize) a limb to disengage from the conflict.

Growth and molting
The Caribbean hermit crab, along with all species of hermit crabs, grows through a strenuous and hazardous process called molting where the exoskeleton of the animal is shed and a new, soft exoskeleton is exposed from beneath. A molt may also allow the crab to regrow lost appendages. The smallest Caribbean hermit crabs will molt many times per year while the largest (about the size of a baseball) may only molt once every 18 months.

Before a molt, the hermit crab will attempt to eat enough to survive the molting period. It will obtain sea salt from salt water to aid in shedding the old exoskeleton and will store a supply of water. The crab may even seek out a smaller, tighter shell for easier digging or a larger shell for room to shed. Normally the molt is started by digging down into the moist substrate (with its shell) and creating a little cave. There total darkness triggers the secretion of the molting hormone ecdysone.

Over a period of up to three months (larger crabs require the most time),

the buried, molting crab sheds the old exoskeleton in a process called ecdysis,
lost appendages may be regrown (completely or partially),
the new exoskeleton hardens,
the old exoskeleton is eaten to recover calcium and other nutrients,
the crab regains its strength and returns to the surface.
Sometimes the land hermit crab will molt on the surface where other crabs may eat the shed exoskeleton or even kill the defenseless, molting crab. Circumstances that may cause a surface molt include illness or the lack of a substrate in which the crab can bury itself.

Land hermit crab reproduction
Female land hermit crabs release fertilized eggs into the ocean where the salt water causes them to hatch. The hatchlings live in the ocean until their gills mature enough to be able to extract oxygen from air.

Once on land, the hermit crab begins to drink fresh water, but still requires salt water (sea salt) for functions like molting. After the last developmental molt, the modified gills lose the ability to process water and the crab can drown if trapped under water.

Captive C. clypeatus will not breed in an indoor environment, but have done so in an outdoor enclosure. None of the young lived past 10 days.

http://en.wikipedia.org/wiki/Caribbean_hermit_crab

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