Nerding out: Sea shells by the sea shore

Emily Shultz
Guest Writer

Photo via

I wouldn’t classify my personal style as gothic. In fact, you can almost always find a bow in my hair and a Lilly Pulitzer planner in my bag. So it could sound surprising that I have an enormous collection of skeletons currently displayed on top of my dresser. Unless I also mentioned that those skeletons use to belong to mollusks, such as snails, clams, oysters and many others. Yeah, I was talking about seashells, scientifically known as the exoskeletons of many marine invertebrates. The hard covering has three distinct layers and are made up of mostly calcium carbonate and 2 percent, or less, protein.

Did you ever wonder where all those seashells that can be found on uncombed beaches, come from? How did they get there? How were they made? When I was a little girl, I was told that the mermaids carved seashells out of rocks found in the bottom of the ocean. I would like to say I didn’t believe it, or that when I reached a capable age I did some research into where seashells actually came from. But that wasn’t the case. It wasn’t until the summer after my freshman year of college as a Marine Biology major, when I was sitting in a lab for a Summer class on Wallops Island, that I found out I was looking at a shell in a egg sack. To be scientifically correct, I wasn’t just looking at a Whelk seashell in a egg sack, it was a marine gastropod mollusk aka a snail. I was most likely the only student sitting there questioning everything they knew about seashells and marine life in general. I tried my best not to act completely dumbfounded when the professor said, “Yes, all seashells are born.” Now when you actually think about it, it’s not that crazy of a concept, all living things have the ability to reproduce and have to come from reproduction. However, shells aren’t alive when you find them on the beach and many people never think of shells before they reach the beach. Therefore, I told myself that it wasn’t that silly of me not to know shells were born…


pearl shell

Photo via

In fact, shells start out as microscopic organisms in an egg sack and grow in conjunction to the invertebrate living inside of them. Because the exoskeleton, the shell, is not shed it gets larger to accommodate the invertebrate’s body growth. Picture this, you are walking along the beach and pick up a pretty large shell. You turn it over in your hand and notice lines or strips on the shell. Those lines or stripes are actually the growth marks. Seashells grow by the invertebrate living inside of it excreting out material, calcium carbonate and a small amount of protein, causing growth outwards at the margins. And why are shells different colors? The color of a shell depends on the diet of the mollusk and the water environment that it lives in. If a mollusk takes in a lot of carotene or ptertodines their shells will often be red, if the shell has brown and black hues the mollusk has taken in melanin.

I was also told that every time a seashell is made a new star is born… I’ll save that topic for another article…


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