Amy Stewart is the author of “The Drunken Botanist: The Plants That Create the World’s Great Drinks” and a forthcoming novel, “Girl Waits with Gun.”

Spirals in Time
The Secret Life and Curious Afterlife of Seashells

By Helen Scales

Bloomsbury Sigma. 304 pp. $27

By this point in the summer (if you’re doing it right), you’ve probably got a seashell or two shedding sand on your front porch. There’s something about the mindlessness of a day at the beach that lends itself to shell-collecting: You stroll along, you spot one and then another; eventually, you start to compare them, then you look for the best one and pretty soon a few of them come home in your pocket.

Most of us don’t give the shells much thought after that. Mine eventually get broken and then swept off the porch, where I tell myself they’ll make good garden fertilizer. But British marine biologist Helen Scales sees a vast and complicated universe inside a shell. These intricate deposits of calcium carbonate contain within them complex mathematical equations, they shelter surprisingly powerful and inventive creatures and they reveal the planet’s history.

‘Spirals in Time: The Secret Life and Curious Afterlife of Seashells’ by Helen Scales (Bloomsbury USA)

“There is nothing quite like a mollusc,” Scales writes, quoting biologist Colin Tudge, and goes on to prove it in this wide-ranging natural history of shell-dwelling aquatic creatures. She begins with a sort of narrative taxonomy of the phylum Mollusca, which delivers its own weird surprises: We learn that a spiky-shelled sea snail is named Alviniconcha strummeri, after Clash drummer Joe Strummer — yes, you’re going to want to Google a photo of that snail — and we discover that cephalopods, such as the weird and wonderful octopus, are actually a type of mollusc that happens to be missing a shell.

But what about those shells? Spirals like the ones found within the chambered nautilus form a shape known as a logarithmic spiral, in which the gaps between each whorl are spaced incrementally farther apart in a precise mathematical manner. These creatures — these faceless, mushy creatures — build shells according to laws of geometry that humans were unable to fully grasp until the 1960s, when early computers could be programmed to calculate every possible shape of shell that could be produced according to the mathematical formulas underpinning them. Scales describes these computer-generated models as an “imaginary museum of all possible shells,” an idea popularized by Richard Dawkins in his 1997 book, “Climbing Mount Improbable.” Here we can see computer-generated models of shells that exist today, those that are long extinct, and those that have not yet evolved but might someday. It’s a bewitching notion, and my only disappointment was that the Museum of All Possible Shells doesn’t actually exist in, say, Chicago, so that I could book a flight.

Scales goes for the surprising and shocking, as she should. There’s a creature called a geography cone snail (a name straight out of a Hogwarts textbook) that will kill seven out of 10 people who pick it up, and others that spit poison-laden teeth at their prey. Some species of shellfish absorb neurotoxins from algae and induce out-of-body experiences — up to and including death. The poison persists in urine, making it possible that “drinking the urine of someone who ate infected Spondylus would get you high.” You go ahead; I’m good with my beer.

But your biggest reward for reading “Spirals in Time” is the chapter on sea silk. Believe it or not, an enormous, gnarly bivalve called Pinna nobilis grows a “beard” of about 1,000 hairs, each the width of a human hair, and those hairs have been woven into cloth. Stories of Egyptian boats powered by sea silk sails and Roman emperors cloaked in sea silk robes might be an exaggeration, but a sea silk hat from the 14th century has been found in a Parisian basement, and the British Museum has in its collection a sea silk glove that belonged to 17th-century scientist Sir Hans Sloane.

Yes. This is a real thing. And Scales, our intrepid reporter, made it all the way to Sant’Antioco, a little island off the southern tip of Italy, where the craft of sea silk weaving is still practiced in a greatly diminished form. She takes us into the home of a local woman who demonstrates the ancient art of soaking the sea silk to remove the sand and salt, then combing it into long strands and spinning it into thread, which can then be woven or used in embroidery.

In case you’re already envisioning your next Oscars gown made of sea silk woven by Italian women on a remote island, you can forget it: The supply is nearly exhausted, thanks to a ban on harvesting the endangered molluscs. New thread becomes available only when a fisherman happens to pull up a dead specimen.

This was the liveliest chapter of the book, and I only wish Scales had put herself into the narrative in this way more often. As interesting as these creatures are, the book could benefit from a few more human specimens to move things along. As with any obscure corner of the natural world, the story is as much about us as it is about them: Whether we are weaving silk from the beard of a bivalve, planting oysters around a contaminated bay to clean up the water or using cowries as currency in the 18th-century slave trade, the story is always, inevitably, about us.