This post explores the biology and ecology of seashells at the beach, including the animals who use them and how they create them. It’s part of a series I’m doing on using everyday situations to help young kids explore science – particularly ecology and biology – more in depth.
As the summer wraps up, many families head out to the beach. While you’re there, use the opportunity to learn about seashells and the creatures that once lived in them.
The scientific context
Seashells provide homes for a variety of animals: oysters, clams, snails, scallops, mussels, and hermit crabs. The shells that wash up on the shore are left over after the animal has died.
Unlike humans, the mollusks that form shells have their skeletons on the outside. These exoskeletons provide a structure for animals’ organs, just like our bones do. (Some insects like grasshoppers also have exoskeletons, which is why their outside is hard.) This is different from turtle shells, which are actually part of and attached to the turtle’s internal skeletons.
Seashells are also made of a very different material than anything human bodies make. Bones are mainly protein with a few minerals, while seashells are mostly minerals.
In addition, seashells grow differently than human bones. Human bones have living cells inside them, allowing them to grow from the inside and heal if they get broken. In contrast, shells have no living cells and can’t repair themselves if they break. Instead, animals with seashells have a special organ that lets out proteins and minerals to form the shell. As the animal grows, it lays down more and more layers across the edges of the shell. The newest section of the shell is actually the part where the animal sticks out its head.
While most animals have shells that grow with them, hermit crabs don’t. They have to scavenge shells left by other animals and move into a new shell when they get too big. In fact, if you have a hermit crab, you can pick out which shell it will use for its home next!
Animals have evolved shells to provide protection from predators. The seashells either completely cover the animals (like with clams) or the animals retreat into them when there is danger (like snails). But some predators have developed ways around this armor. Otters smash clamshells against rocks or use objects to pry them open. Luckily for animals living in seashells, most predators aren’t quite as clever as otters.
Explore it yourself
Seashells are a beautiful doorway into discovering nature at the beach with your child. Here are a few activities you can do:
- Sorting shells by type: With very small children, you can use the many different types of seashells to talk about how they are similar and different. You can sort by shape, color, and size.
- Use them to create “beach art”: We used seashells as turrets for our sandcastles. My son also liked rinsing off the sand and lining them up in row.You can also use them to make spirals, circles, or other shapes in the sand.
- Identify them: You can figure out which kind of animal lived in the shell by examining its shape. These Wikipedia articles on the different types have good photos that can help identify them: bivalve (clam) shells, gastropod (snail) shells, crustatcean (crab, lobster) shells, and horseshoe crab shells. If you really want to get into it, this guide delves into the many different subsets.
While it’s fun to decorate with shells, I don’t recommend bringing them home. In national parks, such as the Cape Cod National Seashore, it’s actually illegal to remove natural features. In other places, it’s just better to leave them there for hermit crabs to use and other people to enjoy.
Questions to Discuss
- What is your favorite shell and why?
- How would it feel to carry your house everywhere with you? What would be the benefits and challenges?
- How do other animals who live in the ocean protect themselves from predators?
Resources for More Information