| 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
|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
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
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."