The eat-or-be-eaten dynamic is one of the reasons shells evolved in the first place, more than 500 million years ago. Calcium, the basic building material, is a major component of seawater, and turning it into housing had obvious protective advantages. Largely for purposes of self-defense, shellfish quickly moved beyond mere shelter to develop a dazzling array of knobs, ribs, spines, teeth, corrugations and thickened edges, all of which serve to make breaking and entering more difficult for predators. This shell-building boom became so widespread, according to a 2003 paper in Science, that the exploitation of calcium carbonate by shellfish may have altered the earth's atmosphere, helping to create the relatively mild conditions in which humans eventually evolved.
Some shellfish also developed chemical defenses. Harasewych opened a museum locker and pulled out a drawerful of slit shells, gorgeous conical whorls of pink and white. "When they're attacked, they secrete large quantities of white mucus," he said. "We're doing work on the chemistry right now. Crabs appear to be repelled by it." Slit shells can repair predator damage, he said, indicating a five-inch-long scar where one shell had patched itself after being attacked by a crab. (Humans also attack, but not so often. A photograph on the cabinet door showed Harasewych in the kitchen with Yoshihiro Goto, the Japanese industrialist who donated much of the museum's slit shell collection. The two celebrated the gift, Harasewych noted, by preparing a slit shell dinner with special knives and sauces. Don't try this at home. "I've eaten well over 400 species of mollusk, and there are maybe a few dozen I'd eat again," said Harasewych. This one was "pretty foul.")
Some shellfish have even evolved to attract and exploit would-be predators. The United States happens to lead the world in biodiversity of freshwater mussels, a generally dull-looking, bad-tasting bunch—but with an astonishing knack for using fish as their incubators. One mussel species trolls a gluey lure in the water as much as a meter away from the mother shell. When a hungry fish snaps up this Trojan horse—it's actually a string of larvae—the larvae break loose and attach themselves to the fish's gills. For the next few weeks, part of the fish's energy goes to feeding these hitchhikers. In another mussel, the edge of the fleshy mantle looks and even twitches like a minnow. But when a fish tries to grab it, the mussel blasts the fish's gaping mouth with larvae. Yet another species, the snuffbox mussel from Pennsylvania's Allegheny River, actually has inward-curving teeth on the shell edge to hold a fish in a headlock while it covers its gills with larvae. Then it lets the bamboozled fish stagger off to brood baby snuffboxes.
A pretty shell, like a pretty face, clearly isn't everything.
Collectors these days tend to be interested in both beauty and behavior, which they sometimes discover firsthand. At the Academy of Natural Sciences in Philadelphia not long ago, collectors at a shell show swapped stories about the perils of fieldwork. A retired doctor had been bitten by a soft-shelled turtle while feeling for freshwater mussels. A diver had suffered an excruciating sting from a bristle worm. A retired pilot said he had had his middle finger ripped down both sides by a moray eel off the coast of Gabon, but added, "It's kind of worth it for a new species."
"New to science?" someone asked.
"The heck with science," he replied. "New to me."
Then the conversation turned to methods for separating mollusks from their shells. One low-tech approach is to leave the shells out for fire ants to clean, but high-tech works too. "Microwave cleaning is the greatest," one collector volunteered. Pressure builds up in the shell, he said, till it "blows the meat right out the aperture"—Phwap!—"like a cap gun."
So much for spiritual repose.
Downstairs at the museum, dealers had laid out a roomful of tables with thousands of microwaved, bleached, oiled and polished specimens. They included some of the most spectacular of the roughly 100,000 mollusk species now known, and they were liable to have come from almost anywhere on earth. A dealer named Richard Goldberg pointed out that animals with shells have been found living in the Marianas Trench, 36,000 feet deep, and in a Himalayan lake 15,000 feet above sea level. Though people tend to think of them as "sea shells," some species can survive even under a cactus in the desert. Goldberg added that he became interested in land snails after years as a seashell collector when a friend dared him to find shells in a New York City backyard. Goldberg turned over a few rocks and came up not just with three tiny land snails, but with three distinct species.