Wondering Where Do Seashells Come From?
Shells Such as Conches and Cowries Come From Animals Called Mollusks
Collecting seashells is a popular childhood pastime that many adults indulge in too. Yet few people stop to think about where seashells come from. Those lovely pieces gathered once belonged to somebody and acted as someone’s shield and home. That somebody would be a mollusk.
What are Mollusks?
Mollusca is one of the largest phyla in the animal kingdom holding about 130,000 species. Animals in the Mollusca phylum are all invertebrates with soft fleshy bodies. These include land snails, octopi, squids, and shell-making creatures such as oysters, scallops and sea snails. Not all mollusks make shells but all shells come from mollusks.
How do Mollusks Make Seashells?
Seashells are made from calcium carbonate. Aquarium owners with shell-making creatures in their tanks would be wise to provide the creatures with calcium, for as mollusks grow so do their shells. In the ocean the chemicals a mollusk needs to make its shell with are dissolved in the sea water. Each mollusk has a structure called a mantle which is a flap of tissue on part of its body. The surface cells of this tissue produce a protein and carbohydrate coating which hardens and becomes the shell. Thus, seashells come from a mollusk's mantle.
Different Mollusks Make Shells of Different Types
In general shells fall into two categories – the flat seashells come from bivalve mollusks and the coiled shells which come from gastropod mollusks. Bivalve mollusks have two shells hinged together such as clams and oysters have. The edge of their shells is the youngest part and the inner side is called nacre or mother-of-pearl. Gastropods such as cowries or conches make the beautiful coiled shells that are prized by so many. In these seashells the youngest part is at the opening, with layers getting successively older farther from the opening. Cowries spread their mantles over the entire shell and deposit an iridescent layer over the entire outer surface of the shell. Young cowries actually have a coiled shell but the nacre coating adults deposit make their surfaces smooth and hides the coiling.
Why Do Mollusks Need Shells?
Mollusks use shells for protection from predators. Many mollusks can withdraw completely or partially into their shell for protection. Shells can also protect against the elements, protecting mollusks from wave damage or drying out from the sun.
Be Careful About Seashell Collecting
When a mollusk dies it leaves behind its shell. Unfortunately shells found in souvenir shops could come from mollusks that were collected and killed. Such shells are best left alone. Shells found on a beach should be checked for inhabitants before becoming part of a collection so that a creature is not deprived of life and home. In fact, it would be far better to just leave the shell where it was found. Remember the old maxim "take only pictures, leave only footprints". The collective impact of many shell collectors can alter the face of a beach.
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