Hermit crab

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iHermit crab
A land hermit crab in Corcovado National Park, Costa Rica.
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Subphylum: Crustacea Class: Malacostraca Order: Decapoda Suborder: Pleocyemata Infraorder: Anomura Superfamily: Paguroidea Latreille, 1802
Families
Coenobitidae Diogenidae Lithodidae Paguridae Parapaguridae Pylochelidae Pylojacquesidae

Hermit crabs are decapod crustaceans of the superfamily Paguroidea ^[1], not closely related to true crabs. Most hermit crabs salvage empty seashells to shelter and protect their soft abdomens, from which they derive the name "hermit". There are about five hundred known species of hermit crabs in the world, most of which are aquatic, living at a range of depths from shallow coral reefs and shorelines to deep bottoms, although some species are terrestrial. A number of species, most notably king crabs, have abandoned seashells for a free-living life; these species have forms similar to true crabs and are known as carcinised hermit crabs. Hermit crabs live in the wild in colonies of 100 or more, and do not thrive in smaller numbers.

Contents 1 Shell competition 2 Development 3 Fossil record 4 Some notable species 5 Hermit crabs as pets 6 References 7 External links

[edit] Shell competition

As hermit crabs grow, they must exchange their shell for a larger one. Since intact gastropod shells are not an unlimited resource, there is frequently strong competition for the available shells, with hermit crabs fighting over shells. The availability of empty shells depends on the abundance of the gastropods and hermit crabs, but most importantly on the frequency of organisms that predate on gastropods but leave the shells intact ^[2]. A hermit crab with a shell which is too tight cannot grow as fast as hermit crabs with well-fitting shells, and is more likely to be eaten ^[3].

[edit] Development

The various species range in size from the Pacific hermit crab, which rarely grows larger than a peach to Coenobita brevamanus which can approach the size of a coconut. Terrestrial hermit crabs begin their lives in the sea but, through a series of moults, develop the ability to breathe air. After the last developmental moult, the young hermit crab will drown if left in water for an indefinite period of time. Their link with the sea is never entirely broken, however, as hermit crabs carry a small amount of water in their shells at all times to keep their abdomen moist and their modified gills hydrated. It is believed that C. brevamanus is the species of Coenobita best adapted to life on land (aside, of course, from Birgus latro).

[edit] Fossil record

The fossil record of in situ hermit crabs using gastropod shells stretches back to the Late Cretaceous. Before that time, at least some hermit crabs used ammonites' shells instead, as shown by a specimen of Palaeopagurus vandenengeli from the Speeton Clay, Yorkshire, UK from the Lower Cretaceous ^[4].

[edit] Some notable species

• Birgus latro, coconut crab
• Ciliopagurus strigatus, Halloween hermit crab
• Coenobita cavipes
• Coenobita clypeatus, Caribbean hermit crab
• Coenobita compressus, Ecuadorian hermit crab
• Coenobita perlatus, strawberry land hermit crab
• Coenobita variabilis, Australian land hermit crab
• Pagurus bernhardus
• Pagurus pollicaris, flat-clawed hermit crab

[edit] Hermit crabs as pets

There are several species of hermit crabs that are common in the marine aquarium trade. These omnivorous or herbivorous species are useful in the household aquarium as scavengers, eating algae and other debris.

The scarlet hermit crab, or red reef hermit crab, Paguristes cadenati, is a handsome and interesting species with a bright red body and yellow eyestalks, and stays rather small (about 2–5 cm / 1–2 inches across). Smaller species of a similar passive nature include the zebra hermit crab (brown legs with white bands), the red-tip crab and blue-legged crab.

In Europe, the common hermit crab, Pagurus bernhardus, is popular.

While most species available in pet stores are small like those listed above, and are simply scavengers, others may grow quite large (some on the Pacific coast can grow to 30 cm / 12 inches) and may eat coral, clams and other crustaceans.

Most marine hermit crabs will appreciate a salinity of between 1.023 and 1.025, and temperatures between 4–14°C (temperate species) and 24–27°C (tropical species), with a good bed, algae to graze on and a variety of shells to change into. They will happily switch shells frequently if given the opportunity - an interesting display to watch.

There are approximately 15 terrestrial species in the world, and, of those, the following are commonly kept as pets: Caribbean hermit crab, Coenobita clypeatus, and the Pacific hermit crab, Coenobita compressus. Other species such as Coenobita brevamanus, Coenobita rugosus, Coenobita perlatus or Coenobita cavipes are less common but growing in availability and popularity as pets.

[edit] References

1. ^ Paguroidea (TSN 345098). Integrated Taxonomic Information System. Accessed on August 12, 2006.
2. ^ Tricarico E. & F. Gherardi (2006). Shell acquisition by hermit crabs: which tactic is more efficient?. Behavioral Ecology and Sociobiology 60 (4): 492–500.
3. ^ Angel, J. E. (2000). Effects of shell fit on the biology of the hermit crab Pagurus longicarpus (Say). Journal of Experimental Marine Biology and Ecology 243 (2): 169–184.
4. ^ Fraaije, R. H. (2003). The oldest in situ hermit crab from the Lower Cretaceous of Speeton, UK. Palaeontology 46: 53–57.

[edit] External links