The Secret, Deadly Life of Seashells

Think seashells are just pretty ocean ornaments? Think again. Shells, and the mollusks that live in them, can be deadly.

Bloomsbury USA/Amazon

Their geometry captivated Sir Christopher Wren, their beauty made them the original blood diamonds, and—along with sharks and bison—they just might hunt and kill you this summer.

I am speaking, of course, about seashells and the creatures that inhabit them, which are the subject of an enlightening and fun new book Spirals in Time: The Secret Life and Curious Afterlife of Seashells by Helen Scales.

The book traces the story of shells on two separate tracks—their role in human history, and their much bigger role in the much grander history of Earth.

“This is not a shell guide or a book on how to find and identify them,” Scales writes. And indeed it is not—Scales is a sly operator. The first 90 percent of the book is full of fascinating anecdotes and nuggets sure to impress your next dinner party. The final chapter, after she has hooked you with these magnificent creations and their unique history and biology, is a call to do more to preserve these creatures that are vital parts of countless ecosystems and a major source of food for humans worldwide.

Mollusks, the creatures that actually build these shells, are an ancient phylum that is estimated to contain 50,000-100,000 known and named living species. The only group containing more species are the arthropods. Not all mollusks make shells—cephalopod mollusks such as octopus, squid, and cuttlefish do not. They can be found pretty much anywhere on the planet, including deserts, miles beneath sea level, and in caves on land nearly a mile deep.

According to Scales, “mollusks first evolved in the ocean at least half a billion years ago.” One of those ancient ones, the Cameroceras, is positively terrifying. Some estimates place this shelled mollusk at more than 30 feet long (Scales uses the double decker bus it would dwarf as a reference).

Weird facts like that are why I am a sucker for books in this genre of histories of a specific item or creature. While they have always existed, they seem to be more popular since Mark Kurklansky’s Salt: A World History came out more than a decade ago.

And Scales’s book is certainly filled with weird facts.

There is the weird biology many of these creatures have developed. Limpets chew their meals off of rocks, and their teeth are apparently made of the strongest biological substance known. In Costa Rica, sea snails have feet that they use essentially as surfboard (and then use those same feet to capture its prey). Or there are the sea butterflies and sea angels, part of the gastropod branch of mollusks. They “bade farewell to the seabed, split their feet into two tiny wings and flitted off into the big blue yonder.” Unfortunately, those sea angels actually hunt and kill sea butterflies in a particularly brutal manner.

Others have developed snorkels, greenhouses (yes they can grow food inside their bodies), and glow-in-the-dark shells. There are vampire snails that suck on the blood of electric rays and some gastropods that shuck other oysters (another mollusk) with a prong from their shells.

For those who already find the male anatomy aggressively present in modern life, steer clear of male argonauts, as they have a detachable penis on the end of one of their eight arms.

Then there is the incredibly deadly variety of cone snail that hunts fish by shooting them with hollow darts loaded with a particularly deadly venom. These same deadly darts can and have been used on humans, to devastating effects.

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Mollusks’ shells, which stay with them and grow from birth until death, is a wonder of Da Vinci Code-esque mathematical profundities and engineering feats. It also can really mess with a mollusk’s sex life. While shell collectors and certain religions revere left-coiling shells, since roughly 90 percent of mollusks have right-coiling ones the left-coilers are screwed, so to speak, because they don’t match up when it comes to mating time.

Human interaction with the mollusk is ancient and varied. The shells have nearly always been a form of decorative jewelry, and for many thousands of years, a form of currency. Perhaps the most notorious of those is the cowrie shell.

In slave markets in West Africa, human flesh could be bought with these beautiful items found in the Indian Ocean. Scales quotes Jan Hogendorn and Marion Johnson’s book The Shell Money of the Slave Trade, which claimed that in the 18th century, 10 billion shells were shipped for this purpose, largely by British traders.

Mollusks have and are still a source of food in all parts of the globe. They have been the source of textiles (sea silk), fertilizer (ammonite), and drugs (to be burnt and consumed with betel nut).

While mollusks have proved themselves to be singularly adaptable creatures throughout their history, one of their major homes, the ocean, faces an uncertain future due to environmental changes. Scales’s book is a timely reminder of just how much we stand to lose if things continue progressing the way they are.