Bermuda land snail

Bermuda Land Snail
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
Subclass:	Orthogastropoda
Superorder:	Heterobranchia
Order:	Pulmonata
Family:	Zonitidae
Genus:	Poecilozonites

The Bermuda land snail is an endemic species of pulmonate land snail that scientists believe colonised the mid-Atlantic island of Bermuda at least 300,000 years ago. It makes up 95% of Bermuda's terrestrial fossils. Only one other large pulmonate Succinea has been found - as a fossil.

Research

The major contributor to the natural history of Poecilozonites is Harvard paleontologist Stephen Jay Gould who did his doctorate and early academic research on Bermuda's snails. Dr. Gould described to the Gazette of first visiting Bermuda as a deckhand on a Woods Hole Research Institute boat in 1959. "I was a geology major. I had a look around and found all these wonderful fossil snails in all their variety. The geology of Bermuda had already been worked out by then and I thought these snails would become a pretty good PhD."

Poecilozonites is a member of the Zonitidae family and is likely to have colonised Bermuda from North America as one specimen via flotsam. Gould cites research which uses the "probability of self-impregnation" as the justification of this view.

Gould claims the proto-poecilozonites "underwent a vigorous and presumably rapid adaptive radiation" and diversified into three subgenera and 15 species, ranging in size from P. nelsoni (max dia. 46 mm) to the subspecies' of P. Gastrelasmus and P. Discozonites which were found to rarely exceed 5 mm. Although extinction of various species occurred in prehistoric times, with the introduction of predators by man in the 1500s, namely hogs, dogs, cats, and rats, the snail suffered, but has apparently hung on.

It was the introduction of the predator snails Euglandina and Gonaxis in the 1950s and 1960s and the increased use of pesticides that led to the presumed extinction of the surviving Poecilozonites' species by the 1970s.

The apparently accidental introduction of the edible snail, Otala in the mid-1920s set the die for the destruction of Poecilozonites as by the 1950s, Otala had become a pest and measures were taken to control their numbers. By the time of Gould's research in the mid-1960s, P. bermudensis and P. circumfirmatus were still common. He wrote of talking to an elderly woman who remembered a time when the shells were collected and burned for lime. By the mid 1970s, a Bermuda Biological Station scientist remembers opening his kitchen door and seeing none other than Gould exclaim "If I could only find one alive!"

In "Eight Little Piggies," a book from 1993, Gould wrote: "I don't even think Euglandina has even dented Otala but it devastated the native Poecilozonites. I used to find them by the thousands throughout the Island. When I returned in 1973... I could not find a single animal alive. Last year (1991) I relocated one species, the smallest and most cryptic, but the large P. bermudensis, the major subject of my research, is probably extinct."

In 1999, Gould was quoted in the Royal Gazette:

"(Poecilozonites) are part of a class that are uniquely found on islands. Islands have these strange fauna because of their isolation. Back when I was studying them, we did not know where they came from or their closest relative. That can be done now with genetic research. Poecilozonites had a very impressive radiation in Bermuda. By far one of the largest for a species. It is a wonderful example of an experiment in local evolution. It's just that people did not realise that with the Euglandina, it would eat other snails too. Not just Otala, which by then had become a pest. No one ever said that Poecilozonites ever caused them trouble. It certainly is a tragic story."

In 2002, a Bermuda Aquarium, Museum and Zoo summer intern was sent out to Gould's old sites and is understood to have found a clutch of survivors. Several dozen snails have been sent to London to aid their propagation.

References

• Gould, Stephen Jay Allometry in Pleistocene land snails from Bermuda: The influence of size upon shape, Journal of Paleontology, v. 40 p. 1131-1141.
• Gould, Stephen Jay (December, 1969) An Evolutionary Microcosm: Pleistocene and recent history of the land snail P. (Poecilozonites) in Bermuda, Bulletin of the Museum of Comparative Zoology, v. 138(7) P. 407-532.
• Gould, Stephen Jay (September 1969) Land Snail Communities and Pleistocene Climates in Bermuda: a Multivariate Analysis of Microgastropod Diversity, Proceedings of the North American Paleontological Convention, p. 486-521.