Snow Crabs

Which of the following ocean creatures has an exoskeleton?

And the answer: snow crabs.

Photo Courtesy: The Fish Site.

An exoskeleton is the external skeleton that supports and protects an animal's body. It's different from an endoskeleton, the type that humans have, which supports from the inside. Animals with exoskeletons include insects such as grasshoppers and ants, and crustaceans like crabs and lobsters.

Exoskeletons are excellent forms of defense for smaller animals such as arthropods (insects and spiders) and crustaceans (lobsters, shrimp, snails and crabs). Most have several segments, each one with a somewhat separate piece of an exoskeleton, so the animal's head and body parts can move separately. The defense is extremely effective – it helps to support the animal's body while functioning somewhat like a portable raincoat that prevents the creature from getting wet or drying out.

You may be wondering: why are humans stuck with measly bones if creatures with exoskeletons get a shield and system of support all at once? Well, for that we must look to gravity: an equivalent external skeleton on a larger creature would be extremely heavy. So heavy that we would barely be able to move or function. Instead, our marrow-filled, light, regenerable bones keep us mobile while holding us together – and get it all done from the inside.

Exoskeletons are generally composed of chitin (a complex polysaccharide that is chemically similar to cellulose) and calcium carbonate (common in rocks and eggshells). As animals with exoskeletons age, their soft inside parts grow but their firm exoskeletons do not. When an animal’s body gets too big for the exoskeleton, it splits open and falls away in a process called molting. Consequently, the animal’s body forms a new exoskeleton.

To learn more about the bones supporting the life on Earth (inside and out), check out the video below.

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Rita Moreno
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