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Hermit crab

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Hermit crab
A hermit crab from Costa Rica.
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Mandibulata
Class: Crustacea
Subclass: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Anomura
Superfamily: Paguroidea
Latreille, 1802

The hermit crab is a type of crab that does not have a very hard shell. Not a true crab, they uses other animals' old shells for protection; they especially like old whelk shells. As the hermit crab grows in size, it must find a larger shell.


The hermit crab is a crustacean, but it is very different from other crustaceans. While most crustaceans are covered from head to tail with a hard exoskeleton, the hermit crab is missing part of its exoskeleton. The back part where its abdomen is located, is soft and squishy. Thus, the minute a hermit crab molts into an adult, it sets out to find a shell in which to live.

To get into the shell, the hermit crab squeezes in backwards, securing itself with its four back legs. The back legs have hooks that anchor the hermit crab into the shell without difficulty. The next four legs are used for walking, while the front two are its chelipeds. The chelipeds are not equal in size: one is big and other is small. The larger one is used for grabbing prey and guarding the entrance to its shell. All together, hermit crabs have a total of ten legs, including the chelipeds and the rear legs used to anchor to the shell.

There are about 500 different species of hermit crabs around the world, and they have different colors, often with patterns like stripes and dots on their bodies. Most hermit crab species live on the ocean floor, but many live on land. Female terrestrial (land based) hermit crabs must return to the sea to breed.


Hermit crabs are omnivores (eating plants and animals) and scavengers (eating dead animals that they find).[1] They eat worms, plankton, and organic debris.

Fossil Record

Hermit crabs first appeared in the Cretaceous period, before the Dinosaurs became extinct (died out). Fossils have been found where they have used Ammonite shells.


The reproductive (sexual) organs of hermit crabs are located near and just below the animal's heart and open to the outside at the base of the last pair of walking legs in the male. In the female, they are located at the base of the middle pair of walking legs. The eggs are carried and hatched in a mass attached to the abdomen inside the shell. The number of eggs is usually large, but depends on the animal's size.

As pets

Basic needs to keep pet Hermit Crabs:

  • Humidity gauges (humidity: 75-85% relative)
  • Temperature gauges (temperature: 70-75 °F)
  • Substrate: sand, coconut fiber (must be deep and soft enough to dig in so that crabs can moult)
  • Minimum of a 5 gallon tank for one crab; and 10 gallon tank for about 20 crabs
  • Shells (shells are changed during growth)
  • Separate moulting tank[dubious – discuss]
  • Fresh water dish
  • Salt water pool for submerging (aquarium salt)


  1. Exploring Creation with Zoology 2 by Jeannie K. Fulbright