Bermuda land snail

Bermuda land snails

Preserved specimen of †P. nelsoni at Naturalis Biodiversity Center.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
Subclass:	Heterobranchia
Order:	Stylommatophora
Family:	Gastrodontidae
Genus:	Poecilozonites O. Boettger, 1884
Species
See text.

Bermuda land snails, scientific name Poecilozonites, are an endemic genus of pulmonate land snail in the family Gastrodontidae (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005). 12 species are known from the fossil record, and 4 of these species (bermudensis, nelsoni, circumfirmatus, reinianus) survived into modern times, but due to the highly negative effects of human development, the extant species has been reduced down to only bermudensis and circumfirmatus.^[1]

Scientists believe that Poecilozonites colonised the mid-Atlantic island of Bermuda at least 300,000 years ago. Poecilozonites makes up 95% of Bermuda's terrestrial fossils. Only one other large pulmonate, Succinea, has been found as a fossil.

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I'm Robert Cameron and I've come down to this riverbank today to show you how to do a banded nail hunt. What we have to do is, firstly, learn to recognise the species we're interested in, to tell them apart from other species and how to go looking for them. So we'll make a start. These snails can be found in lots of different habitats, like hedges or woods, but something like this, a riverbank, with some nettles and reeds, is absolutely ideal for them. They really like this kind of place. But I think we'll be lucky and find something here. So this is a good habitat to look at. If you're lucky, snails sometimes are sitting on the vegetation and if you peer gently... Don't knock the vegetation too hard or they may fall off. And we just go along having a look. Yes, look. Under these reeds there's quite a number. I can see both the species we're interested in straight off. We'll have a look at them in more detail later. But you can see how they're clustering on the undersides of the leaves. Of course, not all the snails will be climbing up the vegetation. Some of them will be sitting on the ground and it's also perfectly possible to use empty shells, so long as they're nice and fresh. So I'm going to have a scout around on the ground, underneath the vegetation, and see what I can find. Here's one live one I've found immediately. And here...just on the edge, there are some dead shells. But you can see they're quite brightly coloured so we can score them very easily. Indeed, you can keep the dead shells as a collection for yourself, if you want. The two species we're interested in are Cepaea hortensis and Cepaea nemoralis. I've just found a Cepaea hortensis here and I know it's a Cepaea hortensis because it's a shell with a white lip to the mouth. But here is a Cepaea nemoralis, the other species we're interested in. You can see, very obviously, that it's got a black lip or very dark brown round the mouth of the shell. That's the most reliable way of telling the two species apart. One problem that we have is that, of course, there are not only the adult-shelled snails I showed you just now. Of course, there are babies. Because the babies don't have a lip, we can't tell which species they are. So when you record for the snail hunt, we want you to only look at the adults that have got a complete lip. If you look closely, I've got two babies here and you can see that apart from being smaller, the shell just ends sharply. There's no lip, either white or black, to be seen. Of course, when you go snail hunting, you're not only going to find the two snails we're really interested in. There are lots of others around and some of them look quite similar. Now I want to tell you something about the varieties and how to score them. The varieties are of two sorts. Firstly, we look at the shell colour and then we look at whether or not there are bands on the shell. Now, as it happens, all these three shells, snails in my hand, are unbanded. You can see the shell is purely one colour all over. The categories we want you to put them in is: Is it a yellow, like this one? Pink, like this one? Or brown, like this one? The other aspects of variation in these snails that we want you to look at is their bands. And here I have the three major varieties that we're asking you to record. Unbanded, which you've seen before when I showed you all the unbanded shells. Single-banded or mid-banded, with one band in the middle. And many-banded, with lots of bands. Once you've collected your snails, we want to record them. You'll have seen the recording sheet on the website. And I collect at least all the live snails up and we can put them back where they came from because they're not doing any harm to anybody and we want to preserve the populations. So I just scatter them back... ...where I'd found them. So we've completed our record card. Now we want to enter it. So we go to the website, we look at "Enter a record," we complete the record sheet, following the instructions and we send it off. And very soon you'll get an acknowledgement back from the MegaLab Centre telling you about your record and about the nearest records to it.

Research

The major contributor to the natural history of Poecilozonites was Harvard paleontologist Stephen Jay Gould who did his doctorate and early academic research on Bermuda's snails. On December 21, 1999, Dr. Gould described to The Royal Gazette of first visiting Bermuda as a deckhand on a Woods Hole Research Center 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 Gastrodontidae 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.^{[clarification needed]} Although extinction of various species occurred in prehistoric times, with the introduction of predators by man in the 16th century, 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."

(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.
— Stephen Jay Gould^[2]

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

Poecilozonites circumfirmatus is protected in Bermuda under the Protected Species Act (2003) and a Protected Species Recovery Plan was published for it in 2010 by the Bermuda Government, Department of Conservation Services.

In 2014 it was reported in The Royal Gazette that a live colony of Poecilozonites bermudensi (greater Bermuda land snail) had been found in an overgrown alley in Hamilton. The colony was apparently isolated from the rest of the island, including the effects of invasive species, by colonizing the alley early on.^[3] A captive breeding program was carried out at Chester Zoo and the Zoological Society of London in the UK, resulting in the release of more than 4,000 snails into nature reserves on the island by June 2019.^[4]

In 2020, Chester Zoo also reintroduced 800 lesser Bermuda land snails to the island, which were thought to have been extinct from the island since 2004.^[5] The IUCN Red List considers both extant species to be Critically Endangered, with P. circumfirmatus being possibly extinct in the wild.^[6]^[7]

Species

Species in the genus Poecilozonites include:^[8]^[9]

Subgenus Poecilozonites:
- Greater Bermuda land snail (Poecilozonites bermudensis)
- †Poecilozonites cupula
- †Poecilozonites dalli
- †Poecilozonites nelsoni
  - †P. n. callosus
  - †P. n. nelsoni
Subgenus Gastrelasmus:
- †Poecilozonites acussitimus
- Lesser Bermuda land snail (Poecilozonites circumfirmatus)
- †Poecilozonites discrepans
†Poecilozonites reinianus

References

^ "Poecilozonites Land Snails". The Department of Environment and Natural Resources. Retrieved 2018-01-12.
^ The Royal Gazette, 1999
^ "Bermuda: 'Extinct' snail found living in alley". BBC News. 27 October 2014.
^ Helen Briggs (13 June 2019). "Bermuda land snail: An animal 'back from the dead'". BBC. Retrieved 13 June 2019.
^ "Chester Zoo conservationists save tiny snails from extinction". ITV News. 2020-03-10. Retrieved 2020-11-25.
^ Ovaska, K. & Outerbridge, M. 2019. Poecilozonites bermudensis. The IUCN Red List of Threatened Species 2019: e.T77145002A77145257. https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T77145002A77145257.en. Accessed on 18 April 2023.
^ Ovaska, K. & Outerbridge, M. 2019. Poecilozonites circumfirmatus. The IUCN Red List of Threatened Species 2019: e.T77149902A77151067. https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T77149902A77151067.en. Accessed on 18 April 2023.
^ Gulick, Addison (1904). "The Fossil Land Shells of Bermuda". Proceedings of the Academy of Natural Sciences of Philadelphia. 56 (2): 406–425. JSTOR 4062982.
^ "Poecilozonites bermudenis". mczbase.mcz.harvard.edu. Retrieved 2018-01-12.

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.
The Royal Gazette, December 21, 1999, p. 1, 7,8
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This page was last edited on 18 April 2023, at 17:33

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