Hermit crabs are a fascinating type of crustacean found in oceans and on land around the world. Their most distinctive feature is their asymmetrical abdomen that is adapted to live inside empty seashells or other hollow objects. Here’s an overview of what hermit crabs look like both inside and outside of their mobile shelters.
Shell-Dwelling Appearance
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When fully retracted into a shell, only the front claws and legs of a hermit crab are visible protruding from the shell opening. The crab uses its clawed legs to clasp onto the inside of the shell.
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The soft abdomen is spirally curved to fit into the spiral shape of a snail shell The tip of the abdomen has a modified shape that allows it to firmly grip the columella of the shell
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Hermit crabs come in many sizes, from species that are only a few millimeters long up to the coconut crab which can be almost 1 meter across. However, they all share the same asymmetrical shape adapted for shell-dwelling.
Shell-Less Appearance
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Without a shell the soft abdomen of a hermit crab is completely exposed. It has a curved asymmetrical shape unlike the symmetrical, calcified abdomens of true crabs.
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The abdomen is the most vulnerable part of the hermit crab which is why they seek shelter. It has a long, narrow segmented form which can be brightly colored or patterned on some species.
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The front legs have large, well-developed claws or pincers. The next pair of legs are simple walking legs, followed by even smaller hind legs on the abdomen. The eyes are on movable stalks.
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Hermit crabs can breathe both on land and underwater using gill structures which must stay moist in order for them to function properly. Terrestrial hermit crabs require access to water to keep their gills damp.
Variations Between Species
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There are over 800 species of hermit crabs that vary in colors, claw shapes, leg structures, and other morphological details. Some have hairy or spiny limbs.
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The terrestrial hermit crabs in the family Coenobitidae have more clubbed front legs with blunt claws adapted for walking on land as opposed to grasping shells.
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Marine hermit crabs may have specialized back legs or other appendages adapted for clinging to sea anemones or other marine life that lives symbiotically with them.
So while hermit crabs have adapted in diverse ways to thrive in aquatic and terrestrial environments, they are united by their telltale asymmetrical shape that allows them to retract into scavenged shells or other hollow objects for protection. Carefully observing a hermit crab without its shell reveals the most about its evolutionary adaptations.
What if they can’t find big enough shell?
If they find themselves in a shell that is too small, and if nothing larger is available, common hermits have the rare ability to decrease in size from moult to moult.
Why does a hermit crab change its shell?
Lacking a protective exoskeleton, a hermit crab uses the vacated shell of a mollusc as a temporary safe house, but must find a series of bigger homes as it grows. Finding a shell exactly the right size can prove difficult, and can result in bizarre house-swap chains.
If a crab locates one that’s not the right size, it will wait nearby until another crab looking for a new shell arrives. When that crab sheds its old home and takes the empty shell, our first crab moves in to that newly vacated one, casting off its own, which is then adopted by a smaller crab… and so on. The number of house- swaps each crab undertakes in its life varies depending on water temperature, habitat and species.
What’s Inside a Hermit Crab Shell?
FAQ
Can you eat a hermit crab?
Yes, hermit crabs are generally considered edible. While not a common food source, some cultures do consume them, particularly the coconut crab.
Do hermit crabs like to be held?
It can greatly stress them out and lead to harm, including them pinching you. They are natural animals of prey and could think you are a predator. You can build trust with your hermit crabs over lots and lots of time and proper care, but even then should rarely ever be held.Oct 28, 2024
Where do hermit crabs mostly live?
Native Habitat
Land hermit crabs live close to the shoreline and must have access to both land and water. They use pools and crevices of sea water to wet their gills and the interiors of their shells, and they reproduce and spend their early stages in water. Other hermit crab species are entirely aquatic.
Do pet hermit crabs bite?
While they don’t bite, remember that they can pinch! This isn’t pleasant and can cause panic in children, so always make sure hermit crabs are handled safely with this in mind.