Crab Anatomy
All About The Crab Anatomy
When it comes to crab anatomy, one thing that most crabs have in common is five pairs of legs. The front two of these are their claws, next are their three walking legs, and then their two swimming legs. The claws are what are used for feeding themselves, burrowing, defending themselves, sending other crabs out of their territory, and mating. The claws are also what will pinch a human should you get in their way.
In crab anatomy, the body of the crab itself is a hard, rigid surface called the exoskeleton. This is called a “chitinous skin,” and it covers the crab’s entire body. As the crab grows, and about once a year as an adult, this hard body will go through a process called molting, or shedding of the exoskeleton. For a little while, the crab will look translucent, like you can see through him. Then he will absorb water, his body will start to swell out and the outside will harden once again. When people talk of a soft-shell crab, it is one that is soft because they are in this state of molting.
The head and thorax of a crab is covered and protected by a layer called a carapace. They can also pull their legs into this covering, and to passing predators they will look like a hard rock and not a crab. The front of the carapace has two eyes, two antennae and the crab’s mouth. Crabs can actually shovel food into their mouth very fast. Depending on the type of crab, some eat just plants (herbivores), others eat just animals (carnivores), and the rest eat both plants and animals (omnivores).
Under the carapace, the crab also has gills. It can process oxygen only if these gills are wet, and that is true for both land and water crabs. That is one of the reasons pet crabs must have very high humidity levels, else they would not be able to breathe. When the shell is taken off a crab while eating it, the gills are discarded and not eaten.
Crabs have an abdomen that actually curves under their body and protects the organs used for reproduction. The female crab has a much wider abdomen than the male. Mating takes place while the female is molting and has a soft shell. The male does not stick around to help with the eggs but will sometimes stay to protect the female until her body has again hardened. She stores the eggs under her abdomen until they are ready to hatch.
Every species of crab has differing amounts of eggs--there can be anywhere from a dozen to over a hundred. When hatched, larvae live on plankton until they age sufficiently to molt and have their first hard body. When they are young, crabs go through this molting process several times a year, but after they reach adulthood, it becomes more of a once a year shedding.