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How Seashells are Made
Have you ever wondered how seashells are created? Those beautiful, perfectly formed little things on the beach? How they seem to just be put on the earth to glitter and shine in the sunlight for you? Well, read on to find out.
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It seems impossible that the shells strewn on the beach ever were part of a living creature. But it’s true. The shell is formed by the mollusk itself. By excreting calcium and protein from its mantle, it forms a hard case around itself which it uses for protection. As the shells get larger so as to accommodate the growing mollusk, three different layers are created: an outer layer of protein, a middle layer of calcium, and finally the inner, pearly coat of nacre (Also known as ‘Mother-of-pearl”).
The shell gets bigger as the mollusk adds the protein-calcium mix at the edges, or margins. With some shells, whorls and chambers form. If you cut those empty shells in half, you’d see big spaces in between the spirals (whorls). Those are called “chambers.” However, other shells don't have any whorls or chambers, such as an oyster's. Instead, these particular mollusks grow a flat, shiny shell, with hinges on one end that hold it shut.
Below: A beautiful spiral shell.
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But there’s another big question. We know how shells are made now—but how do they get their colours? The seashells on the beach aren’t all just plain grey or white. They gleam with all the colours of the rainbow, right? The whorls, the chambers, the protein-mix…that’s all alright, but just how do they get so beautiful?
Shells gain their prettiness from the world around them. If a mollusk was living on orange coral, then the shell would turn that shade of orange. If it was living on sand, it would be some sort of yellowish colour. That’s quite handy for a mollusk who doesn’t want to be noticed by any predators.
What predators, you ask?
Well, quite a few animals are interested in the soft animal inside the shell. Shell-borers, for one, drill through the hard outer layer to get to the poor mollusk encased in it. Starfish also prey on these creatures. By wrapping their arms around the shell, they break it open and feed on the animal. Otters dive down, swim back up with the mollusk in their paws, and then break it open using their belly as a table. Also, oysters, clams and mussels are commonly farmed for pearls, the process of which sadly involves the killing of many mollusks.
Now, for the breeding process. When just hatched, most aquatic mollusks are just little free-swimming larvae called trochophore.
These tiny critters are very basic. Spherical or pear-shaped, they use rings of minuscule hairs called cilia to swim, and have a few simple functions. They have both female and male genes, (which means they can mate with any other mollusk) and once the pair have done just that, the eggs are fertilized, and the process repeats again.
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< Left: a trochophore. You can see the cilia (tiny hairs) in a ring around it.
So, if you’re picking up shells on a beach…spare a thought or two for the little critters who once lived inside them!
