Gastropoda: snails and slugs

Helix aspersa (common garden snail)

Characteristics
Slugs and snails belong to a larger group (or Phylum) known as the Mollusca. Molluscs come in many different forms but are predominantly categorised as soft-bodied animals without body segmentation that often have an external shell made of calcareous material.

Snails and slugs are known as gastropods, which mean 'stomach foot'. This describes the way in which the body and internal organs of slugs and snails has been twisted back so that the stomach lies above the large fleshy foot of these animals. The head is at one end of this foot the snail or slug moves by gliding along a surface of mucus or slime that is produced from glands on the foot. All gastropods have a well-developed head with eyes and 1-2 pairs of tentacles.

Life Cycle
Most gastropods are hermaphrodites, which means that each animal has both male and female reproductive organs in the same body. When two individuals snails or slugs meet they exchange bundles of sperm, usually via a dart into the tissue of the other. Eggs are then usually laid in crevices in the soil or under rocks, while some species may give birth to live young.

Feeding
Most gastropods are herbivores and scavengers feeding on fungi, dead animal material and plant matter such as leaves, stems, bulbs and algae. A few are carnivorous and may prey on other snails. All gastropods feed by using a radula, which is a tongue-like structure covered by rows of rasping teeth.

Habitat
Gastropods are found in a variety of habitats across Australia but favour moist environments. Most native species can be found hiding under logs and rocks, in leaf litter or under the bark of trees. During humid weather or times of rainfall they can be seen foraging for food or looking for mates. Slugs are particularly susceptible to drying out and some snails may wait out a dry period by sealing themselves to a hard surface with dried mucus and staying inactive, this is sometimes known as aestivation. In some agricultural areas of South Australia aestivation by introduced snail species causes problems as huge numbers congregate in crops to aestivate over the hotter months contaminating the harvest.