Snails and slugs (part of the group known as molluscs) are another of nature's recyclers, digesting material from the forest floor or the microscopic material that collects on foliage to release nutrients for use by other living things. The land snails are a large assemblage and there is a wide variety of diets amongst them. Many feed on decomposing material, algae, leaves, mosses or fungi but there is a carnivorous group which prefers to dine on other snails and invertebrates such as earthworms. The molluscs also include other soft bodied marine animals such as squid, octopus, nudibranchs (sea slugs), clams and oysters.
The mouth of a snail contains a small pad covered with tiny, serrated 'teeth' (called a radula) which enables the snail to scrape off matter as if it was using sandpaper to do the job. The head and foot are continuous and move forward with the aid of glands which produce a layer of mucous over which the foot muscle slides. A few families have an operculum which is stuck to the top of the foot when the foot is extended. When the snail retreats into its shell, the operculum becomes a door which closes fast, sealing moisture inside.
There is a group called semi-slugs which don't have an operculum or even much of a shell - their shells are more like hats on top of their bodies. And lastly, there are the slugs which have no shells at all. If they encounter dry conditions, all they can do is shrink the body into a more compact shape and tuck their antennae under to reduce the amount of skin surface that is exposed to the air. The rainforest environment is normally a very favourable place to support a variety of slugs and semi-slugs.
Wet Tropics diversity
The Wet Tropics area is home to over 220 species of terrestrial snails. At least 86 of these are in the micro-snail group - those with shells less than 5mm in diameter. More than half of these land snails have not been formally described yet.
The greatest snail diversity is in two areas - high altitude mountaintops and areas of limestone outcrops. Outcrops such as those at Chillagoe which are outside the rainforest environment still attract a large number of mollusc species because of their plentiful calcium supply and protection from fires. Snail diversity is higher where the soil contains high levels of calcium and where there is a moist climate.
Elsewhere in this site, we have profiled particular species but when discussing the land snails, hardly anything is known about this group. Discovery, description and identification of species' ranges is where most of the work is being done. Many species are known but full names have not yet been given and little else is known except perhaps if the animal is arboreal (a tree snail) or lives in leaf litter.
Rhynchotrochus macgillivrayi is a very pretty tree snail which can often be seen on the Nandroya Falls track in Wooronooran National Park, Palmerston section.
The shell of Fastosarian brazieri is translucent and the soft mantle actually stretches up and over the outside of the shell. Thus, when the snail is sitting on a piece of old wood or rough tree bark, it is beautifully camouflaged. In this photo, the mantle has been drawn back to reveal the shell. This species is common in the Wet Tropics area and can easily be found in Palmerston, the Goldsborough Valley and in some surburbs of Cairns.