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MARGINALIA

The Rarest Snail in the World

Do development and scientific study conflict with conservation?

Pat Shipman

Roadblocks

With these tantalizing bits of information in hand, my husband and I decided to find the rarest snail in the world, if we could. Was it still living, or had it gone extinct since Mike last saw it in 1975? Was it really confined to the Evolvulus plant? Was the dwarf species actually more common than it seemed, rare only because of the difficulty of searching the uncut, dry scrubland? To find the snail and answer our questions, we would have to resolve a few problems. Maynard’s description of his collecting site was vague: “on the west end of Little Cayman, on the eastern most of the two paths that cross the island.” There were three modern candidates for these two paths, one of which is now paved, one of which is still a path and the third of which is enormously overgrown. We opted to search the easy places first. Mike had given a good description of the habitat in which he had found C. nanus and we knew a place that sounded ideal.

The second problem was that neither of us knew enough botany. Evolvulus is in the same family as morning glories but “looks nothing like one,” Mike informed us helpfully. In our photocopy of one of Mike’s publications, the picture of Evolvulus was not clear. Maynard had described the plant as “heathlike” and about “18 inches high.” He mentioned that its small gray leaves were about the same color as the snail shells and gave off a strong odor when crushed. A botanical description of the plant mentioned its “scalelike leaves”—a phrase we did not know how to interpret. Google Images produced wildly varying depictions of plants said to be Evolvulus.

The third complication was that we didn’t intend to take live specimens of such a rare species without a permit, so even if we found the snails, we wouldn’t be able to answer all our questions. For example, if C. nanus and C. pannosum were closely related (which a careful DNA study would reveal—if only we had a DNA lab), perhaps the dwarf species had evolved from the larger one. With more samples of Cerion from other islands, genetic analyses could unravel the fascinating story of the spread and subsequent isolation and evolution of Cerion on different land masses.

There are three main ways a snail could travel from island to island: in the beak or talons of some bird, attached to a floating log or other flotsam during hurricanes, or in a boat, as an inadvertent stowaway. The stowaway concept is not as unlikely as it seems. A number of snails crawled into some of Maynard’s collecting barrels full of corals, and he discovered them when he got home to Newton, Massachusetts. Charmingly, the snails woke up after six months’ travel and crawled around his garden, apparently quite happy, until cold weather came. But such unreliable modes of long-distance transportation mean that snails from islands separated by long water crossings rarely meet. These islands tend to evolve their own endemic species of Cerion. A scientist with the right permits and tools might find a fascinating evolutionary history in the DNA of C. nanus and its relatives. After all, the renowned evolutionary biologist Stephen J. Gould started his career by studying the morphology of Cerion and its adaptability in the Bahamas. But first, we simply wanted to find out if the little snail was still alive.




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