Snails from the Cool Temperate Rainforest of Robertson

Here are some snail images from the same trip on which I helped Bob search for his target Millipede species.
I have received assistance from fellow blogger, "Snail", in tracking down what types of snails these are - at least in general terms. After all, in many cases of "creepie crawlies" identification requires microscopic examination (often of their private parts). So, as an amateur naturalist I would be happy enough to settle for an "approximate" ID. Several I had "sort of guessed" (from Google Image searches), but Snail has done much better than that.

Here is a shallowly curved snail, which is in a group of carnivorous snails. I found this link from Mt Annan Branch of the Royal Botanic Gardens for the Carnivorous Land Snail Austrorhytida capillacea. Here are my own images. Snail has confirmed the identity as "probable".From the underside, you can see how shallow is the shape of its shell, and also how transparent the underside of the shell is. Snail's advice was: "Most of the carnivorous snails (family Rhytidiae) have quite characteristic shells: fine radial ribs on the upper surface and smooth on the underside, with a wide umbilicus." DJW says - So that's why the shell has such a shallow angle about it. It also explains the correctly notes the difference between to upper surface and the lower surface.The next snail is, unfortunately, in the too hard basket. Here it is at about real life size. Tiny!This next one is a cropped image. It is a very tightly curled snail with practically no "angle" on its curl. In other words, it is a flat curl, not a helical shell.
Snail's advice was: "It probably belongs to Charopidae or Punctidae --- both families are widespread in wetter areas. V. common." DJW says - that'll do for me.
Now this is more interesting. When we found these guys, Bob told me that they are in a class of snails known as "semi-slugs". Some in the group have such a reduced shell that it cannot cover the entire animal. Some are reduced to having virtually no shell at all - hence the name. They are in the group of Helicarionids.
Snail was effusive in commenting on this one: "The semi-slug (family Helicarionidae) is probably Helicarion mastersi. I'm a bit vague about the helicarionids because no one has sat down and sorted them out once and for all. Lots of species remain undescribed, so I wouldn't be at all surprised if that turned out to be something unusual. Helicarionds are odd little things. Some species release red slime when irritated. No one's looked at it to see whether it contain repellent chemicals or makes the animal too slippery to hold. (Several camaenids do this as well). Other species thrash about when disturbed. And --- apparently --- another one from SE Qld, I think, sticks itself to the underside of leaves --- by its shell not its foot. The mantle encloses the shell and makes a sort of suction cup. Haven't witnessed this but I've been assured it's true!

Here is another of the same species which I found on a tree trunk.
It was last year, in June, on a really wet day.
The snail was out in the open,
"hoovering" over the fine covering of lichen and algae
on the trunk of the tree.

Snail adds: "Not all helicarionids are semi-slugs, btw, but you can distinguish the fully-shelled species from similar ones in other families by the shape of the rear end. In helicarionids it's pinched vertically into a tail. In the others, it's tapered or flat."

DJW Says: What can I add? That comment on the tail being "pinched vertically" was made without the benefit of Snail seeing this image, which I took last year. It looks right to me.
The Australian Faunal Directory does add the following information: Helicarion mastersi subspecies mastersi. This species is found in closed forest, on coastal NSW, from Sydney to Kiama. Spot on, everybody (I live on the coastal escarpment just above Kiama).

These last group of snails had me most intrigued. When I developed the images on the computer, I realised that what had looked like a rough surface of the shell turned out to be a series of fine barbs or rasp-like protrusions on the shell. I started to get excited about this, but what would I know? - I am not a student of snails.

Click to enlarge all these following images, to see the detail.

Snail came through with the goods on this: "The last one belongs to Camaenidae. Probably Austrochloritis metuenda. I thought at first it was A. brevipila, but the books say that this only occurs from Dorrigo to the Border Ranges. Austrochloritis metuenda is an Illawarra species, so that sounds more likely.Snail continues: "The hairs are amazing. They seem to be part of the periostracum, which is the protein layer that overlies the main calcium carbonate shell. The hairs are quite persistent but once they rub off (usually in long dead shells) you can see that they sit on little bumps on the main shell. I am always impressed at how neatly they're arranged."

You can see what is meant by that comment, if you enlarge this image.
Look at the upper edge of the shell.
You can see between the lines of the hairs or barbs.

In a later email exchange, these comments emerged:
Snail wrote - they are called "periostracal hairs".
I did a Google search on that term, and found a discussion of these hairs on a marine mollusc, where it was suggested that it helps as a defence against predators, or other marine creatures, such as Limpets attaching themselves to the marine snail. That made me think.

Subsequently I wrote back:
DJW: Having seen some of the creatures which share these rotten logs (with these Snails), anything to keep them at bay would help.

Snail replied: "A friend of mine did some work on a similar situation with very small snails in the tropics of Borneo. They aren't hairy but have little vanes that seem to act as a protection against tiny carnivorous slugs that scrape through the shell to get to the juicy snaily goodness inside.

http://snailseyeview.blogspot.com/2006/09/heres-some-real-science-from-deepest.html

"I don't know what might be the equivalent in your neck of the woods. I would have thought that most animals would go for the shell aperture but if the snail is clamped down on something and the predator isn't strong enough to dislodge it, then maybe those hairs would prevent them getting their teeth stuck in."
Here is the under-side of the shell, and if you enlarge the image, you can see the barbs or hairs, shining in the light of the flash.
By the way, the Australian Faunal Directory says this snail is found in tall forests, under logs, NSW South-east Coastal regions. Once again, a pretty accurate record.

Conclusion: What started out as an adventure in search of Millipedes has ended up being a discovery tour on Snails as well as a variety of other arthropods, and even lizards, living in wet logs on the forest floor.
Thanks to Bob for the original inspiration, and to Snail for the expert advice on these Snails. It has been a fun learning experience over the last week. I hope my readers have also enjoyed this journey of discovery.

Denis