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An underground snail

September 21, 2013

A couple of weeks ago, I wrote about my modern mollusc survey at the archaeological site I have been working on, and mentioned that I had also seen Cecilioides acicula, a snail which lives underground, while excavating. I managed to take a picture of a live animal on my phone:

Live Cecilioides acicula

Cecilioides acicula – not a great photo, but you may just be able to see the white body of the snail protruding from the shell

As a subterranean species, C. acicula is problematic for archaeologists. It can occur in quite large numbers in samples, but is usually regarded as intrusive. I took a level of the spot I found this snail, and found it was living 90 cms under the former ground surface. In the seminal Land Snails in Archaeology (1972, 186), the late Professor John G. Evans reports that they have been seen 2 metres below the ground surface.

The shells are typically translucent, becoming opaque some time after the snail has died. Here are two very translucent (and quite pretty!) shells from a prehistoric sample elsewhere in Somerset – they are clearly a recent intrusion.

Translucent Cecilioides acicula shells

Translucent Cecilioides acicula shells

They are usually described as a medieval introduction to Britain from Europe (eg. Davies 2010, 170). I have only ever seen them in sediments with a good deal of sand or silt in the mix, and Evans (1972, 186) notes that they “are common in areas which have been cultivated recently but often absent from longstanding grassland which would appear to provide suitable habitats”. I’m interested to know more precisely when they arrived, and how they have come to be spread. In post-industrial Britain, it is not hard to envisage them being spread in soil with potted plants, but if they are truly a medieval introduction, was soil being moved around, or did they spread by some other means? Suggestions very welcome!

References

Davies, P., 2010. Land and freshwater molluscs. In T. O’Connor and N.Sykes, eds. Extinctions and Invasions: a social history of the British fauna. Oxford: Windgather Press. pp.175-180.

Evans, J.G., 1972. Land Snails in Archaeology. London: Seminar Press

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