Marine Biology

The Importance of a Shell for Crustaceans and Mollusks



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Crustaceans and mollusks are both soft-bodied animals who usually live in shells. Their shells protect them from all kinds of hazards in the wild, like predators and temperature changes. Shells are also sometimes used for storing food and as a means to get around in the water. Each animal has specific purposes for it's shell that help it survive in a natural environment.

A shell says a lot about who an animal is and what it needs; by knowing what different kinds of shells are used for, you can easily see why shells are so important to crustaceans and mollusks.

CRUSTACEANS AND THEIR SHELLS
Crustaceans use their shell as an exoskeleton; they don't have bones inside their bodies, so they need something to protect their soft tissue. Nutrients in the crustacean's diet help a healthy exoskeleton develop - the harder the shell is, the safer they are inside. Crustacean shells differ from mollusk shells, though, because crustaceans are different - they've usually got legs and arms in addition to a central body, and most shelled mollusks do not.

Crabs are an example of crustaceans who use their shells for many things - having a rigid shell helps them capture food, move around the ocean floor, and stay safe from hungry predators.

Shedding is a normal process for crustaceans. Once the shell starts getting too small for the animal inside, a crustacean will start to grow a new one right underneath the one they're already wearing. When the new shell is ready, the old one comes off. The new shell is soft for a few days, which makes the crustacean vulnerable - they generally hide out until it hardens.

Shells are extremely useful for these soft-bodied marine animals - they provide a barrier between the crustacean and whatever wants to eat it, and they provide stability and support for crustacean muscles.

MOLLUSKS AND THEIR SHELLS
Mollusks use their shells for protection, as well. Just like crustaceans, they produce a hard shell that goes on the outside of their bodies (with a few exceptions). However, mollusks have simpler bodies than crustaceans, so their shells are quite a bit different.

Since mollusks don't shed like crustaceans do, their shell has to get bigger as they grow. Usually mollusks just add on to what they already have - calcium in their foods helps new pieces of shell develop. Without this protective covering, many mollusks would be in serious trouble.

Mollusks need their shells for lots of things - shells can help them get around, carry their babies, and dig holes in the sea floor. A solid, hard shell can also let a predator know that they're not going to enjoy trying to eat one of these soft-bodied creatures, too.

Why are shells so important to crustaceans and mollusks? In a nutshell (or clamshell, if you prefer) - without them, the soft bodies inside would have no insurance against becoming a sea turtle's dinner. In addition to predator protection, shells provide ways for crustaceans and mollusks to move, burrow, and eat.

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