Gastropods
What are gastropods?
Gastropods are soft-bodied animals without body segmentation. Some species have an external shell made of calcareous material for protection.
Gastropods belong to the mollusc group. Molluscs include snails, slugs, octopus, shellfish and other species.
Molluscs are the second largest group of invertebrates after arthropods with around 85,000 species.
Gastropods are characterised by having three main body areas – a head, mantle and tail. Snails have an additional area called a visceral mass contained in the shell.
Cockles are a type of mollusc. They are protected by a hard outer shell.
Case study – red triangle slug
Appearance
The red triangle slug is the largest native land slug in Australia. It has a breathing hole in its distinctive red triangle on its back and eyes on stalks.
Red triangle slugs move by gliding along a surface of mucus that is produced from glands on the foot. It can grow up to 14 centimetres long.
Most native Australian slugs only have two eye stalks compared to four on introduced species.
Habitat
Red triangle slugs are found in damp environments in various habitats including city gardens, forests and woodlands.
Red triangle slugs hide in the leaf litter or under bark. They will emerge after rain looking for food.
Diet
The red triangle slug feeds on microscopic algae growing on tree trunks and rocks. It will even eat algae growing on fences, pavers and household walls.
Red triangle slugs create distinctive 'chain-link' patterns as they feed on algae on tree trunks.
Role in the ecosystem
Red triangle slugs are an important food source for birds, bats and lizards.
Blue tongue lizards are one of the animals that prey on red triangle slugs.
Red triangle slug anatomy
Slugs are hermaphrodites. This means they are both male and female.
Head and mantle
Red triangle slugs have a mouth with thousands of tiny teeth called radula. They use their radula to scrape algae off smooth surfaces.
They have two optical tentacles which are retractable with light sensitive eye spots. They are also used for smelling and feeling the surrounding environment.
The respiratory pore, or pneumostome, is used for breathing. It is located in the red triangle mark on their back. This is part of the slug's mantle.
The mantle is made of a thicker flesh than the head. When frightened or not active the slug retracts its head toward the mantle for protection.
The red triangle on the slug is designed to warn off and deter predators.
Tail and foot
The tail of the slug starts at the end of its mantle and continues along its body.
The underside of a slug is called the foot. Slugs move by muscular contraction of the foot.
The breathing hole of the red triangle slug is visible in its red triangle. The red triangle is designed to deter predators.
Invertebrate explorer digital book
Find out more
Written by teachers, the invertebrate explorer digital book explores the incredible world of Australian invertebrates.
Students can use the book to investigate classification, features, adaptations and habitats of a variety of Australian invertebrates through narrated videos, stunning images, interactive activities and detailed text.
Content supports living things, Australian animals and class studies on invertebrates.