The Importance Of Being A Mollusk
One animal has eyes and can change color at will. Another spends its life rooted to one location at the bottom of the ocean. The third spends its days chewing lettuce in a garden. These animals seem vastly different, yet all three are mollusks, a category of animal that includes an astonishing range of organisms.
Having colonized land and ocean, garden and tidepool, mollusks exemplify how life adapts, evolves, moves into new niches. In 2004, for instance, the Marine Ecology Progress Series journal reported that blue mussels had been discovered in Svalbard, a chain of islands in Norway. Since blue mussels thrive in warmer temperatures, marine biologists believed that their presence in Arctic waters indicated climate change. At the same time, mollusks contain within themselves chemical compounds that can be used to make medicine. Seaslugs and cone shells, for instance, produce toxins that have been useful in the development of cancer-fighting drugs.
The word “mollusk” stems from a Greek word meaning “soft,” and seems to be one of the only characteristics shared by all mollusks. In general, the phylum Mollusca is defined by a body plan. Mollusks have mantles, a fold of soft tissue on the dorsal, or top, side of the organism. Mantles produce both shells and dorsal plates by secreting calcium carbonate, a molecule formed when atoms of oxygen, calcium, and carbon combine in precise proportions. (Though it might sound exotic, calcium carbonate is the same substance in Rolaids.) The mantles of some mollusks also produce a complex protein – a kind of molecule that serves many purposes in all living creatures – called “conchiolin,” which forms a tough superstructure that houses the calcium carbonate shell.
Of course, every rule has an exception, and the world of mollusks is no different. Sometimes, mollusk mantles do not produce shells at all. Think of a slug’s back, and the slimy, shimmery part that seems different from the rest of the slug’s body. That is the mantle without a shell. A slug is a snail that has broken the rules.
In addition, most mollusks have a mantle cavity, an open space that, depending where the mollusk lives, allows fresh water, saltwater, or air to flow through it. The animal’s anus and genitals open into the cavity, so as water or air passes through, it transports waste material away from the animal, and allows mollusk eggs and sperm to mix.
A good place to plumb the world of mollusks is the Natural History Museum of Los Angeles County (NHMLAC). Set on a sprawling campus south of the University of Southern California, the NHMLAC has the largest collection of mollusks in California, and the third-largest collection in the United States (only behind the Smithsonian and Philadelphia’s Academy of Natural Sciences). Less than one percent of the museum’s mollusk collection is on view at any one time, and the total collection numbers over 500,000 lots. A lot is generally a group of specimens from any one location, so the total number of individual specimens is far higher.
One hot day, I visit the museum to talk with Lindsey Groves, collections manager of the museum’s mollusk department. I duck into the staff entrance early to escape the heat, and a few minutes later Groves walks down from his office to meet me. He is wearing jeans, sneakers, and a plaid, long-sleeved shirt, and has a full head of white hair that covers his ears. A trim, white mustache sits under his nose. His museum name badge is tattered.
I want to ask him how he became a mollusk maven. Why does he think learning about octopi make anyone’s life any better? Why would I need to know anything else about a scallop besides how well it’s been cooked?
Growing up in the San Fernando Valley, Groves notes that his parents encouraged him to learn about the natural world.
“This led to bringing home lots and lots of objects for further study and appreciation,” he said. “This collection of collections included rocks, minerals, fossils, coins, stamps, insects, bones, baseball cards, and, of course shells. So it is befitting that I now manage one of the largest shell collections in the US and the world.”
In other words, he had become a museum collections manager before he finished high school.
As a lover of mollusks, Groves is not alone. Throughout history, mankind has periodically felt the call of the mollusk. In seventeenth-century Holland, shell-collecting became a mania. One collector stipulated on his death-bed that his shell collection be kept in a chest secured by three different locks, whose keys would be kept by three different men. Only when all three men were present could the chest be opened for a potential buyer. Shell collectors began hiring touch-up painters to touch up the flaws in their shells. Shell auctioneers did well, too, since as collectors died, their collections would come onto the market, waiting to be snatched up by new shell enthusiasts.
Mollusks even enchanted Oliver Wendell Holmes, one of the 19th-century Fireside Poets, a group whose members included William Cullen Bryant and Henry Wadsworth Longfellow. Holmes wrote “The Chambered Nautilus,” about a mollusk of ancient lineage that lives in a chunky cream-and-red shell, and may have shared the oceans with aquatic dinosaurs. He refers to the nautilus as the “ship of pearl, which, poets feign / Sail the unshadowed main.” Mollusks tend to have many lovers, seducing biologists and poets alike.
After our introduction in the lobby, Groves takes me to his office on the museum’s third floor. As we walk to the door, I think not of marine biology, but of film noir: the wooden door has a frosted-glass window with “Malacology” stenciled in the middle. I almost expect to see Humphrey Bogart inside, feet on the desk, examining a snail. Inside, however, is no private investigator. Instead, I see a room dedicated to mollusk-study.
Groves’s desk is tucked into one corner of the room; on top of the desk are a computer and microscope. Marine biology journals sit on shelves extending from floor to ceiling. Cabinets upon cabinets are filled with mollusk specimens. Groves opens one of the cabinet drawers, revealing boxes of tiny shells, and glass vials with specimens gathered from Pacific expeditions. Some of the larger shells retain small imprints of muscles left behind by the long-dead creatures that lived inside them. They look like brown smudges, or smears of old chewing gum.
Groves stresses that mollusks are “more than just pretty shells.”
“Mollusks are vital components of the ecosystem,” he tells me. Since some mollusk species are particularly susceptible to pollutants, one can measure the impact of human activity on the environment by monitoring mollusk populations.
When a population of mollusks disappears, Groves says, “you can be fairly certain that high levels of these chemicals have been reached, and may indicate that commercial species may not be healthy to consume.”
In addition to helping malacologists gauge the health of the environment, mollusks provide clues to the history of life on Earth.
“Mollusks are studied to help understand the evolution of life,” Groves says, “as mollusks first appeared in the Cambrian Period (about 490 to 500 million years ago) and are an integral part of the fossil record.”
As we talk, Groves takes down a glass jar from a shelf behind me. In it is a chiton, an oval-shaped mollusk that is armor-plated like an alligator. Chitons live in the sea, and belong to a class of mollusk called Polyplacophora, but to me it looks like a prehistoric pad of steel wool, something Fred Flintstone might have used to scrub his pots. It has an otherworldy weirdness: Where is the mouth? Which end is the front?
When alive, Groves explains, a chiton inches along on a single muscular foot; when bothered, it can curl into a ball with its protective plates on the outside. Chitons eat algae scraped from rocks by their radula, an organ like a tongue, but with hard, tooth-like structures on top.
Mollusks comprise such a hugely diverse class of animals that Groves has a hard time explaining what, exactly, differentiates them from other things that crawl or swim in the sea.
“They aren’t easy to define,” he says, understatedly.
Some mollusks, like the magnificent Syrinx aruanus, a member of the gastropod class, look like the traditional seashell. The Syrinx, though, is the largest snail in the world, and can reach weights of up to 18 kilograms. Try taking that home from a beach vacation. Other mollusks – the aplacophora – lack shells completely. The squid, another mollusk, also lacks a shell. Instead, it has a cuttlebone, a hard structure buried deep within its body. The scaphopods look like tiny tusks. And, the bivalves range from the oyster, which can fit comfortably in the hand, to the giant clam, which can weigh 400 pounds.
Aside from the 400-pound behemoths, and fortunately for malacologists, most mollusks fit in jars and boxes. Soft-tissue specimens must be preserved, however, and how mollusk specimens are preserved turns out to be crucial to malacology. Stored properly, a specimen can yield data for legions of malacologists. Stored improperly, a specimen can fall apart, turning to mush.
Groves explains that most specimens today are preserved in 95 percent ethyl alcohol, the pure form of alcohol found in thermometers and medicine cabinets. Ethyl alcohol, or ethanol, is clear, and maintains the structural integrity of the mollusk. Older specimens, however, were preserved in formalin, a solution of formaldehyde in water. Formaldehyde has been used as a tissue preservative for decades, but because formaldehyde eats away at calcium carbonate, the specimens’ shells have a tendency to fall apart. The formaldehyde preservative also degrades the specimen’s DNA, making genetic research impossible. Even more important for marine biologists to know, it is a carcinogen.
Next door to Groves’s office is a room filled with preserved, mostly dry, specimens. They are housed in storage cabinets that line the walls on three sides, and Groves begins opening drawer after drawer of dried mollusks. The first drawer contains chambered nautilus shells, lined up in neat rows. The drawer below it is filled with nothing but squid beaks. Groves lets me hold the hard, black objects, and feel the sharp edges.
“That one could give you quite a nip,” he says.
Below the squid beaks is a drawer containing the egg case of the paper nautilus, a small octopus that creates a curved structure reminiscent of the chambered nautilus, but much thinner. I pick up an egg case: it feels as light and airy as balsa wood.
But these treasures are nothing compared to the wonders kept behind a door at the end of a corridor outside Groves’s office. This is the door to the storage room, where metal storage cabinets are stacked four high and ten deep, and crowd out everything else in the space. I immediately think of the final scene in Indiana Jones and the Raiders of the Lost Ark, when the camera pans out to show an enormous warehouse filled with untold treasures. But, in this room, the treasures are shells, remnants of marine creatures that long ago were scooped up by marine biologists or private enthusiasts.
Groves begins unlocking cabinets and sliding out drawers, each filled with more specimens of twisty shells and labeled glass vials. The unmistakable scent of formaldehyde wafts from each drawer he opens, and I ask him about it. Doesn’t it bother him? He shrugs.
“We get used to the smell,” he says.
As I follow Groves around the crowded room, I realize that, sometimes, the wonder of mollusks lies not in what they contribute to medicine, or how they illuminate evolution. Sometimes people fall in love with mollusks because of their eeriness, their alienness, their tentacles and hard outer casings filled with whorls and covered with delicate patterns. We walk around to the other side of the room, where Groves opens a cabinet and pulls out a heavy jar, one foot tall, containing a preserved octopus.
“The kids love this one,” he says, referring to children of friends who he sometimes shows around. “We aren’t sure what kind of octopus it is, but we are afraid to open the jar to find out. It’s so old it might break.”
Mollusks show tremendous diversity even within each of their subgroups. Think of the stereotypical octopus, with eight long arms and a bulbous head, hiding among rocks or a coral reef. In truth, there are many other kinds of octopi in the ocean. In another cabinet, Groves shows me a species of octopus that looks short and squat, like one of the enemy ghosts in Pac-Man. Its tentacles are only a couple of centimeters long, and two horn-like protuberances jut out from the top of its head. This octopus lives at the bottom of the ocean, 1,000 feet down, and moves along the sand, instead of swimming through the water as other octopi sometimes do; its stubby tentacles are well adapted to the bottom-dwelling lifestyle. Other octopi have been known to deceive predators by walking along the sea floor on two tentacles, looking very much not like an octopus.
Deception also occurs in the world of shell-dealing. Groves notes that dealers will sometimes alter their wares to increase the chance of sale. To illustrate his case, he pulls out a Syrinx, a creamy-colored shell as long as a person’s forearm.
“Here, you can see where the seller cut away a part of the shell that might have been cracked, or otherwise imperfect,” he says. He points out the edge of the outermost whorl, which looks too perfectly straight and smooth to have occurred naturally. “But, it’s still a nice shell.”
After spending a day with Lindsey Groves, I understand more fully how well mollusks have adapted to their environments, and how much variety phylum Mollusca contains. I also have a better appreciation of conservation. Who knows where the next miracle drug will come from? Maybe a small snail living on the sands in the middle of the Atlantic will contain within its body a chemical that slows the advance of Alzheimer’s disease. After all, penicillin – a potent antibiotic and one of the most significant medical products of the past 100 years – comes from mold.
Mollusks demonstrate that, along with countless examples of beauty, Nature is filled with potentially useful biochemistry. More than just a pretty shell, indeed.