Hermit Crab

Description:

Decapod Crustacean of the superfamily Paguroidea. This species has no shell, as is common with most crabs. It has a soft abdomen, which is normally protected by a shell. To protect the abdomen, this crab takes empty seashells, into which it can enter and hold for protection of its body as a whole. That pictured is a larger size than most I have seen.

Habitat:

This crab was spotted on a night dive on a coral reef at the north end of the Turks and Caicos Islands. I took a quick photo just before surfacing, at about 50 ft, which turned out to be the best photo of the day.

Notes:

The second photo above shows a hermit with a smaller shell. Per the attached Wikipedia article..."As hermit crabs grow, they require larger shells. Since suitable shells are sometimes a limited resource, vigorous competition often occurs among hermit crabs for shells. The availability of empty shells at any given place depends on the relative abundance of gastropods and hermit crabs, matched for size. An equally important issue is the population of organisms that prey upon gastropods and leave the shells intact. Hermit crabs kept together may fight or kill a competitor to gain access to the shell they favor. However, if the crabs vary significantly in size, the occurrence of fights over empty shells will decrease or remain nonexistent. Hermit crabs with too-small shells cannot grow as fast as those with well-fitting shells, and are more likely to be eaten if they cannot retract completely into the shell. As the hermit crab grows in size, it must find a larger shell and abandon the previous one. Several hermit crab species, both terrestrial and marine, have been observed forming a vacancy chain to exchange shells. When an individual crab finds a new empty shell it will leave its own shell and inspect the vacant shell for size. If the shell is found to be too large, the crab goes back to its own shell and then waits by the vacant shell for anything up to 8 hours. As new crabs arrive they also inspect the shell and, if it is too big, wait with the others, forming a group of up to 20 individuals, holding onto each other in a line from the largest to the smallest crab. As soon as a crab arrives that is the right size for the vacant shell and claims it, leaving its old shell vacant, then all the crabs in the queue swiftly exchange shells in sequence, each one moving up to the next size. Hermit crabs often "gang up" on one of their species with what they perceive to be a better shell, and pry its shell away from it before competing for it until one takes it over."