Snail of the Week

Late yesterday afternoon I spent an hour or so poking around at the base of trees just to the east of Alice Springs at two small gaps in the MacDonnell Ranges. The whole district – indeed almost the whole of central Australia – has had unprecedented rains this year so it is a good season for many taxa – including the land snails.

My mate Mark Carter is a local tour guide – and a great one at that – who also has an interest in snails in general and the land snails of central Australia in particular. So yesterday we went for a drive – only about 10 kilometres from the Alice Springs CBD – and within a few minutes found two very rare species that have very restricted distributions and about which we know bugger all. And these two are not alone, because there is a paucity of research into the numbers, distribution and variety of our land snails in this country.

Some of these issues are discussed in a valuable piece of research titled Between a rock and a dry place: land snails in arid Australia by Cameron Slatyer, Winston Ponder, Daniel Rosauer and Lyndell Davis (published in Animals of Arid Australia: out on their own? 2007. Royal Zoological Society of New South Wales, Mosman, NSW). There the authors note in conclusion that:

Arid and semi-arid land snails have been found in a wide region of inland Australia. Diversity of land snails in terms of both endemism and richness in such environments were found to be strongly correlated with areas of sharp topographic relief and to a lesser extent, limestone outcrops. It is suggested that the relict nature of land snail species in arid and semi-arid Australia, their dependence on high soil moisture and their relative ease of collection and identification, in combination, make them excellent indicators for arid and semi-arid refugia. A number of important areas for land snail conservation were identified based on species richness, endemism and richness at generic or family level. These were (in order of priority) West MacDonnell Ranges, Flinders Ranges, Musgrave Ranges, Lawn Hill-Camooweal area, Peterman Ranges, Burrup Peninsula, Cape Range, Shark Bay and Fitzroy Crossing.

So, back to the Jessie Gap Hairy Snail. The Northern Territory Parks and Wildlife Commission has this interesting Factsheet that tells us that Semotrachia jessiena is:

…a small to medium-sized (shell diameter 10-12mm) camaenid land snail, with nearly flat spire…Like the related S. emilia in nearby Emily Gap, this snail has been found only under a single small group of fig trees, this time in Jessie Gap in the MacDonnell Ranges, east of Alice Springs.

…

There is no published information on the ecology of this species, other than that the collected specimens were found while aestivating on small rocks in litter under a small patch of figs. This site is in well-shaded rubble moistened by seepage at the side of a near permanent pool (Solem 1993).

Just over the road from Jessie Gap Mark and I spent some time poking around under some scattered Mulga trees, looking for another rare – and undescribed – land snail that lives in a very delicate moist environment at the base of these trees. We were looking for a local Succinea sp. (Amber Snail). This genus has a worldwide distribution but the exact species we have around Alice is unclear – there may be several. After poking around for a while at the base of one of the trees we found three individuals munching down on the cryptogams that live a very tenuous existence in the shade of undisturbed (by cattle, people etc) soil at the base of the Mulgas.

Mark told me that cryptogams (no, not crytograms, which a type of puzzle which consists of a short piece of encrypted text) are:

…tiny soil crust plants like cyanobacteria, fungi, lichens, bryophytes. These communities are pretty important in deserts worldwide but (of course) there is not much known about them. For more information see https://www.soilcrust.org/crust101.htm. When these habitats are wet they are sometime described as having a biofilm. The Semotrachia also eat this film but usually when it grows on rocks or wood rather than soil. Fires trash these mini-plant communities – bushfires are the main threat to snails here – it directly cooks the animals and destroys their food. In the long run I’d like get around to trying to identify some of the main crust plants they eat but that might be impossible. I’m told there hasn’t been a lichenologist through central Australia in living memory so I suspect few species here are named.

That’s all from me for now – if you want to have a look at these snails – and more – for yourself get in touch with Mark Carter at DesertLife – the Red Centre wildlife specialist by calling him on +61(0)447358045 or sending him an email at mark@desertlife.com.au. DesertLife’s website is here.

Here is another pic of the little Succinea spp.