Unsurprisingly, these snails are hard to spot. To find them, Barna Páll-Gergely, a land snail taxonomist at the Eötvös Loránd Research Network in Budapest, Hungary, and his colleagues gathered soil samples from caves and placed them in a bucket of water. They then removed the floating debris, dried it, sieved it and examined it under a microscope. “I cleaned the shells under the microscope with very precise brushes used by nail artists,” says Páll-Gergely.
The snails probably didn’t live in the caves though, says Páll-Gergely. “We assume that the sediment had fallen in through crevices in the rock, because it contains bleached, opaque shells of surface-dwelling terrestrial gastropods. The living snails presumably live deep in limestone crevices close to or on root systems.”
The researchers also discovered a not-quite-so-tiny snail in Laos, naming it Angustopila coprologos, after the Ancient Greek word for “dung gatherer”. Standing a mighty 0.51 mm tall, it seems to arrange tiny granules of mud – possibly its own faeces – in a pattern of radial lines on the surface of its shell.
The snails’ miniature size does give them advantages. “It is probable that by being small, these snails can reach food particles no other species can consume and enter very narrow rock crevices,” says Páll-Gergely. They could also avoid predation by being smaller than the things their predators normally look for, he says.
Is A. psammion likely to be the smallest land snail possible? Finding anything smaller will be increasingly difficult, says Páll-Gergely.
There are smaller known snails in the sea – the record holder there is Ammonicera minortalis, with a diameter of between 0.34 mm and 0.46 mm, he says. That is probably close to the lower limit, which is determined by the number of neurons a newborn snail must have to be functional, and the shell of the adult snail being large enough to accommodate at least one egg.
Journal reference: Contributions to Zoology, DOI: 10.1163/18759866-bja10025
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