The Shell Seeker

Introduction

Pick up a shell at the beach; any shell at all. Does it speak to you? What is it saying? It’s likely we seek shells because every one tells a story. But not just a single story. A shell is an entire library in the palm of your hand. Most of the shells you find are made by mollusks, the most diverse of all marine animals. It’s estimated that there are 100,000 different species alive today, but that’s probably an underestimate by half. While not all mollusks make shells (think slugs), each of the shells made by every one of these species has its own unique shape, color, size, and texture.

Shells are the story of the eons of evolution that fashioned them into the vast variety of shapes we see in them: from an angel’s wing to a child’s top; from an egg to a comb, a horn, or a pelican’s foot. The creativity of evolution honed these forms, not so that we can marvel at their beauty—although we do—but so the animal who formed them can survive.

A shell is a mollusk’s protection; its defense against drying out and a structure on which to hang its muscles. It may have points and spires that make it hard for predators to gain purchase. It may be thin and angled, so it can slip through sand or bury into the mud, or it may be wide and flanged, so that it doesn’t sink. Every shell shape, no matter how streamlined or intricate, is an architectural story of success.

Shell shapes

You can tell a lot about the story of the animal that lived in a shell with a few quick observations. The most important: is it paired or single?

A paired shell means the animal was a bivalve—one of roughly one seventh of all mollusks. This clam, scallop, mussel, or oyster lived its life sandwiched between two hinged shells. It could crawl around a bit, but was largely stationary, unless it was a scallop. They slam their shells shut with such force it creates a jet, setting them aloft. Bivalves don’t hunt. They eat using tubelike siphons, pumping in water and filtering it with a set of delicate gills, sustaining themselves with a plankton buffet. Bivalves are the ocean’s quiet—but inordinately effective—cleaners.

A single shell means the mollusk was most likely a gastropod. These snails account for three-fourths of the mollusk species and their stories vary wildly. A smooth, egg-shaped cowrie grew up in the tropics, was a vegetarian as a juvenile but might have eaten coral and sponges as an adult. If you find a hole drilled in a shell it was likely bored by a moon snail or a whelk, which have special mouthparts for piercing their prey. The elegant cone snail attacks with a toxic spear. Meanwhile, the corpulent conch grazes algae and hops giddily over the seafloor.

A few cephalopods, relatives of the squid and octopus, also grow a hard cover. In this book we’ll meet two of them, each with their own story of what it takes to swim the seas in a shell.

Shell Life Stories

If you’re holding a shell, turn it around in your hand. See if you can trace its story back to the beginning. Find the tiny bit at the pointy apex if it’s a gastropod or the rounded umbo if it’s a bivalve. That nascent nub of shell cradled the mollusk at the beginning of its life. Imagine what that was like for the animal as it metamorphosed like a butterfly from larva to an adult. For most mollusks, its world changed forever in that moment, leaving its youthful, wandering ways in the plankton and settling on the seafloor, a rock, or a pier.

Look closer at the shell’s changes in colors and striations. Built molecule by molecule, every shell records the chemistry of the oceans in which it lives. Like tree rings, those layers tell us about changes to our world, about hotter summers or cooler winters, about seasons with plenty to eat and seasons without. These records might require scientific tools to read, but the stories are there just the same, embedded in the atomic and crystalline structure of every shell.

Trace a path away from the shell’s point of origin. Look for scars, dents, or encrustations. Perhaps this shell was more than a home for the mollusk that made it. Can you spot the thin, round tube left by a feather worm, the remains of a barnacle, the stains of algae? Can you see a hole drilled by a predator? Can you see the stories of an entire community in the shell?

Even after the animal who created it is gone, a shell’s story is far from over. It may become home for another animal, like a hermit crab. If it becomes incorporated into a reef, it will also bolster coastal protection, keeping our homes safe from storms.

Otherwise, a shell may roll around on the seafloor, breaking into smaller and smaller pieces. Over time, it turns to sand and rebuilds the beach. It creates a sandy habitat for the same kinds of worms, clams, and seaweeds that the animal itself once grazed upon, an endless cycle of renewal.

Or the shell might become buried in the mud. Over the millennia, it becomes a fossil—as many as 100,000 species of fossil mollusks have been identified—its calcium and carbonate replaced by silica and other minerals but maintaining the form of the shell. One day, it may be lifted high onto a mountain, where winds and rain reveal its form again.

Perhaps before the shell becomes part of a reef, returns to sand, or becomes engulfed in mud, a wave lifts it into the water and deposits it on the beach. The tide peels back and leaves it exposed to the air, and that’s when the shell’s story crosses your path. You pick it up and consider the momentary intersection of worlds: one terrestrial and one marine; one alive and one caught up in the great geological cycle of our planet.

Shells Speak to Humans

Shells are also a story of us. The simple act of picking up a shell connects us with humans as far back as we existed, or even earlier. The first known artwork—a few etched lines on the canvas of a freshwater mussel shell—dates back 500,000 years to Homo erectus. We probably began eating the animals that lived inside shells back then too. The first known shell jewelry was strung together and draped across someone’s neck some 100,000 years ago. The first shell instrument was filled with human breath 18,000 years ago. We traded shells for clothing, tools, and food at least 2,000 years ago and the money cowrie became the common currency of the Pacific six centuries ago.

Over time, we associated shells with status, spirituality, and art. Ancient people were obsessed with the blue and purple dyes produced by some mollusks, and the color came to represent royalty. Shells were incorporated into the stories of gods, like Venus rising from the clamshell. Scallops became the metaphor of the pilgrim’s journey. Shells were the muse for artists such as Georgia O’Keeffe and Salvador Dali and inspired entire movements, like Art Deco and Rococo.

In sixteenth-century Europe, wealthy collectors prized the rarest shells brought back from voyages to the Pacific. They were displayed as centerpieces of their personal menageries, curiosity cabinets that signaled social standing. Eventually, those shell collections became the foundations for our modern museums of science, our collective legacy, and our urge to pick up and hold on to the natural world.

It’s hard not to see something of ourselves in the fascinating stories of the animals who build shells. They become a metaphor for our strengths and weaknesses, our challenges and aspirations.

Mussels, which form dense aggregations where young settle on top of the old, recognizing an environment conducive to success, remind us of the importance of connection to each other. Limpets, which wear tiny imprints in the rock where they live, remind us of the comfort of home and a place to call your own. Cone snails, with their fierce venom, warn us not to be fooled by beauty, which can sometimes disguise danger. Circular moon snails, which lay their eggs in circular egg cases called collars in the sand, remind us of the reliable return of tides, seasons, and life.

Pearl oysters reveal how imperfection and struggle produce the most prized of treasures. The massive abalone, with its powerful foot that holds fast to the rocks, teaches us about tenacity and strength, even as their populations dwindle. The mysterious story of sea silk, a golden fabric made from the byssus of the Mediterranean’s noble pen shell, reinforces what it means to try to find balance between what we take and what we leave in the sea.

The great gift of the world’s wondrous variety of shells is that no matter how many you collect, admire, or discover along your way, more of their beautiful story is always waiting to be found.