Chances are that you’ve probably picked up a shell while walking on a beach and wondered, “Where did this come from and what made this pattern?” or "Who lived inside here?" Each shell is a mystery we can unravel. But you'll have to read on to find out how!
Our first clue is that shells are made almost entirely out of calcium carbonate or chitin. There are no living cells in a shell such as blood vessels and nerves. This means that a creature with a seashell can not feel anything that hits the shell. This is not true for a turtle, though, which has a shell but is part of their internal skeleton.
Humans don’t have chitin in their bodies but in animals that have it, it helps generate a hard outer shell or armor for protection. And I mean good protection. Most shells have three layers so the creatures that lived in a shell had lots of protection from predators.
To understand what type of creature would need outside protection, think about which creatures would need it most for survival. In the world of living creatures, there are two main categories. You can be a vertebrate like humans, cats, birds, and reptiles, which means you have a backbone. Or you can be an invertebrate, which means you don’t have a backbone for support and so you might need some extra protection on the outside, such as, shall we say...a shell!
Invertebrates that would be found in the ocean and other bodies of water include mollusks (a group of soft-bodied animals that includes snails, clams, scallops, oysters, and sea slugs), horseshoe crabs, cephalopods (cuttlefish, squids, and octopuses), sea urchins and other invertebrates. All of these animals have different types of shells! Cool fact is that most cephalopods have internal shells!
But with a sea of shells on most beaches, how can you tell what creature once lived inside? The answer is that you can tell what creature formed a shell by looking at its pattern and shape. Invertebrates have evolved to have the type of shell that helps them best survive in their environment. For example, some shells help protect the invertebrate against predators, while others are designed to make it easier for the invertebrate to dig down fast with its foot (yes some have muscular feet) to get away. The color of the shell depends mainly on the invertebrate’s diet.
In fact, different types of shells have different names depending on what creature made the shell.
You know those swirly horn-like shells you always find? Those shells have been made by a sea snail such as the costate horn snail, ladder horn snail, barring horn snail, and many more species!
Also, that sand dollar you found when you went to the beach IS ACTUALLY THE EXOSKELETON OF A LIVING CREATURE. The creature will use tiny spines to move around and catch food and when it dies its skeleton will wash up on the shore, that's why there are so many of them.
Also, the sand dollar will stand straight up to catch food that is washed into them, but in a storm, it will lie flat so it doesn’t get blown away. That explains why they are so perfectly flat!
Cute hermit crabs are tricky. They take the shell of a gastropod, aka a sea snail, and use it to protect their soft stomachs. So sometimes the animal just takes another shell and doesn’t make their own.
The shape and design of shells are what makes us pick them up to look at, maybe collect or even turn them into jewelry in the first place (please don't do this!). What makes a shell such a beautiful, swirling thing? The reason is that the shell was a constantly evolving piece of work! Invertebrates like snails and other mollusks have to make space for their growing body or they will be too cramped in their shell. So they have to gradually enlarge and extend their shells by adding new layers of the shell, which give it the swirly, curly pattern. When you look at a shell, the newest part of the seashell is around the opening where the animal (used to) poke out.
And what about the question of why we find shells on the beach in the first place? I mean, don’t the animals need these suits of armor for something as important as survival? The fact is that a shell is the old home and protection of a creature. It has outgrown it (or it may have died). When a mollusk dies, the soft body disappears but its shell remains and eventually washes up on the shore. This is how seashells end up on the beach. Also, once a creature grows out of a shell, it will find another shell to live in and then eventually grow out of that one. Once they grow out of a shell they will leave it behind and if it’s not picked up by another creature it will wash up on the beach. And that is why you see so many on the beach.
Another mystery of shells is why there are different types of shells on different beaches. Turns out the answer is quite simple. Different species of snails, mollusks, etc prefer different habitats. So if a beach has a lot of one kind of shell on it, that means that a certain species likes that kind of habitat.
The beach with the most shells in the world is called Sanibel Island in Florida. It has so many shells that it’s literally called the shell capital of the world. It is also a barrier island that runs east to west.
Now that we have uncovered the mystery of shells, it’s your turn to do some shell investigations! The next time you are around shells, pick one up and look closely at it. Try to figure out what species used to live in it? Pick four shells to observe!
The study of seashells is part of conchology.
Did you know the oldest hermit crab shell is 130 million years old?
Also, the shells you see in shops are not found on beaches, they are from an animal that was killed by a human for its shell. So maybe if you see someone buying one you should warn them that they are killing a living creature.
What you can do to help shells
#1 Try not to collect them because then another creature can’t have it. Take a photo or make a drawing instead!
#2 Definitely don't buy shells because every time you buy a shell from a store you kill an animal!
I hope you enjoyed reading about shells! Thanks for reading!
—Calvin (age 11)