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Snail crawls out of obscurity
Kevin Bonham (k_bonham@tassie.net.au)

Of the many Tasmanian snails discovered and named in the nineteenth century, one of the most obscure has been the species described by Petterd (1879) as Helix lottah. Petterd wrote that this 2.5 mm wide, very flat snail lived at 'Cataract Hill, near Launceston, on the under surface of large boulders' and also that it was 'extremely rare'. As well as collecting a handful of specimens at Cataract, Petterd also picked some up at Conara. Where could that have been, when Conara is now surrounded by dry woodland? Could it be that the creek gully which the intersection of the Fingal and Midlands Highway crosses was once wet forest? Or was the find further afield, for instance near Hummocky Hills?

Anyway, nothing was seen of lottah for over a century after that and the name gradually fell into disuse, being eventually lumped with the far commoner 'Discocharopa' mimosa (Petterd, 1879). (It actually does look a lot like an albino mimosa but there are minor sculptural and shape differences as well as the different colour.) Then in June 2000 I found a small white juvenile dead snail on the underside of a large rock in a degraded portion of the main creek gully at Cataract Gorge (the one which the Duck Reach track follows up from the kiosk.) Eventually I managed to work out that this grotty specimen was the infamous lottah.

On 6 Sep 2002 I decided to spend an afternoon searching the area for more specimens of this species. There are areas of Cataract Gorge in quite good condition, and areas that are utterly degraded, and this gully is closer to the latter. About 90% of the snails and millipedes I saw in the gully were introduced and natives were distinctly scarce. Nonetheless I managed to find two live and six dead lottah specimens in two hours of searching, showing that the species, while scarce, is still common enough to be found. The specimens were somewhat clustered with one rock having one live and three dead specimens, and another having three dead shells. All specimens were under quite large rocks, typically around 50cm wide.

How has lottah survived when most other native snails in the area have been mostly replaced by exotics? Possibly its specialised habitat preference represents a niche that the exotics haven't yet occupied. The preference for large rocks could represent many things - for instance the snail's flatness and small size could allow it to hide in compact earth under large rocks and thus escape larger predators. It could also be a defence against minor fires. The clustering of specimens in varying states of decay suggests the species may spend much of its life cycle under a single rock.

So lottah was back from obscurity, but imagine my surprise when Karen Richards (Forest Practices Board) then brought me some vials of small snails collected from a property near Notley Gorge while searching unsuccessfully for the (other) Cataract Gorge Snail Pasmaditta jungermanniae (also Petterd, 1879), three days before my lottah find. Yes, these vials contained one live and one dead lottah.

So, in three days, a snail that had not been seen alive for the entire twentieth century was found alive twice by different people, one looking specifically for it and one not, one looking in a known site and one not, each completely unaware of the other's search efforts - an amusing coincidence.

Following are pictures of one of the Cataract Gorge lottah specimens. To distinguish it from other tiny white Tasmanian snails in the same size range, what you're looking for is the protoconch (the early whorls before the shell starts growing its adult sculpture). On lottah the protoconch is larger than for most species (two full turns of the spiral) and rather than having radial or spiral sculpture, it looks dull and granular. The very wide umbilicus (the gap between the whorls underneath the shell) and the very flat shell are two other things to look for.

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