Hermit crabs are fascinating little creatures that have captured people’s imaginations for ages. But if you’ve never seen one up close, you may be wondering – what does a hermit crab look like? In this guide, we’ll explore everything about the unique appearance of these charismatic crustaceans.
The Basic Hermit Crab Body Plan
Hermit crabs belong to the crustacean family which includes crabs lobsters, and shrimp. Like all crustaceans, they have a hard exoskeleton, jointed legs, and antennae. Hermit crabs have ten legs – five pairs. The front pair of legs has large claws for defense and feeding.
Hermit crabs come in many sizes, ranging from a tiny 1/4 inch up to the size of a coconut! Most of the 1100+ species are quite small though, between 1 to 3 inches long. Their bodies are asymmetrical, with one claw larger than the other.
A Soft Abdomen Tucked Inside a Shell
The defining feature of hermit crabs is their soft, vulnerable abdomen. Unlike other crabs, hermit crabs cannot fully retract their abdomens into a hard shell. So they borrow empty seashells or other hollow objects to protect this soft part of their bodies.
Their abdomens are specially adapted to clasp onto the inner spiral of snail shells. They use their tail and hindmost legs to secure themselves inside the portable shelter of the shell. Without this borrowed armor they would be easy prey for predators.
Modified Gill Structures
Hermit crabs also have modified gill structures compared to other aquatic crustaceans. Their gills serve a dual purpose – in addition to breathing, they must keep the crab’s abdomen moist. So hermit crab gills have vascularized areas that absorb water.
This adaptation allows hermit crabs to spend time out of water. As long as they periodically dip into water, they can survive on land by keeping the gills and shell interior damp. Some species even reproduce on land near coastal areas.
Stalked Eyes and Antennae
Hermit crabs have stalked eyes that give them excellent vision. Their eyes can rotate 360 degrees for a wide field of view. Two pairs of antennae help the crabs smell, taste, and sense their environment.
A longer pair of antennae detects vibrations and allows the crab to feel around. A shorter pair, covered in sensory hairs, picks up scents and tastes. The antennae help the crabs find food, mates, and shells.
Color and Markings
Hermit crab species exhibit all sorts of colors and patterns. Some are muted and camouflaged in grays, greens, browns or black, while others sport vivid orange or red claws. Some have striking stripes or banding. Color can also indicate a recent molt – newly molted crabs appear bright blue before their new exoskeleton hardens and darkens.
Their hard shells camouflage well on land, and provide warning coloration advertising their claws’ crushing power. But soft or colorful abdomens tucked inside the shells help camouflage in aquatic areas while mating and reproducing.
Important Adaptations
- Asymmetrical body with one large claw
- Ten legs, including large front claws
- Stalked, rotating eyes
- Two pairs of sensing antennae
- Armored front half, soft abdomen
- Modified gills that also absorb water
- Ability to use shells or objects as mobile shelters
So next time you come across a little crab scuttling around with a seashell on its back, you’ll know exactly what a fascinating hermit crab looks like! Their specialized bodies allow them to survive both on land and in water in a portable fortress – one small crab within its adopted mobile home.
