Anatomy

Hermit crabs are unique and entertaining pets. They have an interesting anatomy that helps explain many of their actions and behaviors.

Abdomen
A crab’s abdomen does not have a hard exoskeleton. It leaves a crab vulnerable which is why a hermit crab covers its abdomen with a shell.

Antennae
The antennae are the hermit crab’s sense organs and allow him to gather information about his surroundings. Their are two long and two short antennae on its head. The long pair is used to touch and feel. The short pair is used to smell and taste.

Cephalthorax
The cephalthorax is the head and thorax of the crab which are fused together. The top of the cephalthorax has a hard protective exoskeleton. The eyes, mouth, and antennae are on the head and the legs attach to the thorax.

Exoskeleton
The exoskeleton is made of layers of protein and chitin. Parts of the exoskeleton are hard and other parts are thin to allow movement. A hermit crab’s exoskeleton provides defenses against predators and aids in preventing water loss.

Eyes
A crab’s eyes are attached to eye stalks that can move. The eyes have many lenses so a hermit crab sees many pieces of an image.

Gills
A crab has gills that are located in a branchial chamber. The gills and chamber act like a lung and must remain moist in order for a crab to breath. Even though hermit crab’s have gills, they can drown if kept underwater.

Hairs
Crab’s have hairs between the joints of the legs. They are not true hars and are actually extensions of the exoskeleton.

Legs
A hermit crab has five pairs of legs with different functions. The first pair of legs have the large claws which are used for climbing, fighting, and covering the shell opening. The second pair of legs are used for walking and detecting food. The third pair of legs are also used for walking. The fourth and fifth pair are small legs that are used to hold a crab inside his shell.

Maxillipeds
Around a crab’s mouth are several small appendages called maxillipeds. The maxillipeds are used to hold and tear food as well as for grooming.

Pleopods
The small appendages located on the left side of the abdomen are called pleopods. A female hermit crabs attaches her eggs to the small hairs on the pleopods.

Uropods
Uropods are small appendages located at the end of the abdomen. They are used to hook onto the shell and help the crab grip the shell.