<P> Most species have long, spirally curved abdomens, which are soft, unlike the hard, calcified abdomens seen in related crustaceans . The vulnerable abdomen is protected from predators by a salvaged empty seashell carried by the hermit crab, into which its whole body can retract . Most frequently, hermit crabs use the shells of sea snails (although the shells of bivalves and scaphopods and even hollow pieces of wood and stone are used by some species). The tip of the hermit crab's abdomen is adapted to clasp strongly onto the columella of the snail shell . Most hermit crabs are nocturnal . </P> <P> Hermit crabs can be divided into two groups: </P> <Ul> <Li> The first group is the marine hermit crabs (with a single species, Clibanarius fonticola, in freshwater). These crabs spend most of their life underwater as aquatic animals, live in varying depths of saltwater from shallow reefs and shorelines to deep sea bottoms and rarely leave for land . As pets, several marine species of hermit crabs are common in the marine aquarium trade . They are commonly kept in reef fish tanks . They breathe through gills but they don't have to carry around their water to do so . Most can survive briefly out of water as long as their gills are damp . However, this ability is not as developed as it is in land hermit crabs . A few species do not use a "mobile home" and inhabit immobile structures left by polychaete worms, vermetid gastropods, corals, and sponges . </Li> <Li> The second group, the land hermit crabs, spend most of their life on land as terrestrial species in tropical areas, though even they require access to both freshwater and saltwater to keep their gills damp or wet to survive and to reproduce . They belong to the family Coenobitidae . Of the approximately 15 terrestrial species of genus Coenobita in the world, the following are commonly kept as pets: Caribbean hermit crab (Coenobita clypeatus), Australian land hermit crab (Coenobita variabilis), and the Ecuadorian hermit crab (Coenobita compressus). Other species, such as Coenobita brevimanus, Coenobita rugosus, Coenobita perlatus or Coenobita cavipes, are less common but growing in availability and popularity as pets . </Li> </Ul> <Li> The first group is the marine hermit crabs (with a single species, Clibanarius fonticola, in freshwater). These crabs spend most of their life underwater as aquatic animals, live in varying depths of saltwater from shallow reefs and shorelines to deep sea bottoms and rarely leave for land . As pets, several marine species of hermit crabs are common in the marine aquarium trade . They are commonly kept in reef fish tanks . They breathe through gills but they don't have to carry around their water to do so . Most can survive briefly out of water as long as their gills are damp . However, this ability is not as developed as it is in land hermit crabs . A few species do not use a "mobile home" and inhabit immobile structures left by polychaete worms, vermetid gastropods, corals, and sponges . </Li>

Where do hermit crabs live in the wild
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