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  Cerion - a very special snail in The Bahamas

Cerion is a snail of many shapes. It varies from long and narrow to almost 'golf-ball' shaped. In the past scientists have identified some 600 species of Cerion. Stephen Jay Gould only ever found two distinct forms in the Bahamas at  one location - one large and one small. These were found on Inagua. 

He found thicker ribbed solid coloured shells on rocky coasts exposed to surf. In sheltered bays and inland  he found thin ribless mottled shells. With less exposure to the elements, and the possibility of greater predation by birds, the smooth shells were ideally suited to their different environment.

This page comes as the result of a happy coincidence when I received the photos of the snail Cerion on this page. They were taken by Patrick Wilson of Alaska who loves to visit the southernmost island of Inagua , taking  photographs of its diverse scenery and wildlife.

Many years ago, I was fortunate to have met the eminent biologist, the late Stephen Jay Gould - a prolific writer with more than 300 articles in 'Natural History' magazine and the author of more than 30 popular books on Science. Professor Gould was an evolutionary theorist at Harvard University. He stayed at my house in Nassau several times while en route to Inagua where he was studying Cerion. His enthusiasm for such a lowly organism was infectious over dinner, and from that time I have always looked at snails in a different light. 

Stephen Jay Gould 
1941 - 2002

Early in his career, Stephen Jay Gould worked with Niles Eldredge. Eldredge worked with fossils while Gould carried out much of his work on the living land snail Cerion. He studied this species all over the Bahamas and the Caribbean. Together they formulated the 'punctuated equilibrium' theory which modified Darwin's theory of evolution. Darwin suggested that  evolution was a slow, gradual process.  Gould and Eldridge propose a somewhat different idea, that evolution takes place in short, sudden leaps, between which are long periods of stability. Of course the word 'sudden' must be used in context - it means possibly thousands of years rather than millions.

A Cerion snail on a Prickly Pear
 ( Opuntia ) cactus on Inagua

Professor Gould's work in the Bahamas - particularly in Inagua with Cerion, provided further evidence for the punctuated evolution  theory.

Although much of the evidence for the punctuated equilibrium theory came from fossils, Gould explained  in an interview :  " The fossil record is ninety or more percent invertebrates. I like snails because that's what I work on, and I like Cerion because that's where my expertise is. I'm mostly interested in creatures that can teach us things about how evolution works. And dinosaurs aren't, for the most part, great at that."

The discovery of Cerion was fortuitous, and occurred as he walked along a beach on Inagua: "I was enormously lucky," Gould said. "It's rare to find such a continuous record unbroken by time and erosion."


R. Attrill 2006