Hermit Crab Anatomy: External and Internal Organs

I’ve always found hermit crabs to be intriguing little creatures. From my childhood memories of watching them scuttle across the sandy beach to adopting a few as pets in later years, their unique anatomy never ceased to amaze me.

It is with great pleasure that I share with you my personal experiences and findings on hermit crab anatomy, focusing on the Coenobita clypeatus, which is commonly referred to as the purple pincher crab, PP, or Caribbean crab.

The External Anatomical Features

Hermit crabs have an assortment of external features, each with its own function. Let’s take a look at some of the essential parts that make up their unique anatomy.

Antennae and Antennules

One of the first things I noticed about hermit crabs is their pairs of antennae. The longer outer pair, often referred to as “feelers,” help the crab navigate its surroundings through touch. The inner “bent” pair, known as antennules, enable the crab to taste and smell. I discovered this firsthand when I started hand-feeding my pet crabs!

Compound Eyes

Hermit crabs’ compound eyes are another fascinating facet of their anatomy. Comprised of faceted lenses and located on movable stalks, these eyes are especially adept at detecting fine movements. This feature, combined with their curious nature, makes hermit crabs excellent explorers.

Maxillipeds and Chelipeds

Hermit crabs use their maxillipeds, or mouthparts, to manipulate food and for grooming. My pet crabs often clean each other, which I find to be a delightful sight.

The chelipeds, or claws, have various functions depending on their size. The larger left claw is mainly used for defense and to seal off the shell opening effectively. Meanwhile, the smaller right claw is essential for feeding and scooping water up to the maxillipeds.

Pereiopods (Legs)

Technically, hermit crabs have ten legs, including their chelipeds. Among these are:

  • 2nd and 3rd pair: Walking legs used for movement
  • 4th pair: Stubby legs that help the crab move in and out of its shell
  • 5th pair: Gill grooming appendages vital for cleaning the gills and removing excrement from the shell


Though not immediately apparent, setae, or sensory hairs on the exoskeleton, are another essential component of a hermit crab’s anatomy. These hairs help them gather information about their environment.

The Internal Anatomical Features

Hermit crabs’ unique anatomy is not limited to their external appearance. I’ve learned that they have several fascinating internal structures and functions as well.


Unlike many other types of crabs, hermit crabs have modified gills housed in the brachial chamber, located between the 4th and 5th periopods. These gills must be kept moist, a unique adaptation to their predominantly terrestrial lifestyle.

Abdomen and Pleopods

The abdomen, or tail, is the soft portion of the hermit crab, protected within a shell. It houses their digestive and reproductive organs. I learned that female hermit crabs have pleopods, feathery appendages on the left side of the abdomen used for carrying eggs.

Uropods and Telson

In my experience with hermit crabs, one of the most fascinating features is their uropods, appendages at the tip of their abdomen, which help secure them within their shells. The telson, or the tip of the tail, ends in the anus.

The Importance of Shells

A vital aspect of hermit crab anatomy is their dependence on shells for protection. Their soft abdomens make them vulnerable to predators, and a suitable shell is essential for their survival. As a hermit crab enthusiast, I’ve always been interested in providing my pets with the best possible shells.


By far, the most intriguing aspect of hermit crab anatomy is their ability to molt, shedding their exoskeleton to grow. In my experience, molting is a crucial time for hermit crabs, and they require optimal conditions for a successful molt.

It is essential to provide hermit crabs with the necessary humidity, temperature, and substrate. I’ve also learned to be patient, as molting can take several days or even weeks, depending on the crab’s size.

Final Thoughts

Hermit crabs’ unique anatomy continues to fascinate me. From their curious external features to their incredible internal organs and molting ability, these little creatures are a marvel of nature. I hope my personal journey in exploring hermit crab anatomy has been as insightful and enjoyable for you as it has been for me.

avatar Noah
I’m Noah, chief editor at VIVO Pets and the proud owner of a playful, energetic husky (Max). I’ve been a volunteer at Rex Animal Rescue for over 2 years. I love learning and writing about different animals that can be kept as pets. read more...

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