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Gastropods

Gastropods

What are gastropods?

Gastropods are soft-bodied animals without body segmentation. Some species have an external shell made of calcareous material for protection. 

Garden snail
Image: Gastropods are characterised by having three main body areas - a head, mantle and tail. Slugs have an additional area called a visceral mass contained in the shell.
Shells
Image: Cockles are a type of mollusc. They are protected by a hard outer shell.

Gastropods belong to the mollusc group. Molluscs include snails, slugs, octopus, shellfish and other species. 

Molluscs are the second largest group of invertebrates after athropods with around 85 000 species.

Case study: Red triangle slug

Appearance 

The red triangle slug is the largest land slug in Australia. It has a breathing hole in its distinctive red triangle on its back and eyes on stalks. It moves by gliding along a surface of mucus that is produced from glands on the foot. It can grow up to 14cm long.

Red triangle slug
Image: 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 slug habitat
Image: 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 mould growing on fences, pavers and household walls. 

Red triangle slug feeding trails
Image: Red triangle slugs create distinctive patterns as they feed on algae on trees.

Role in the ecosystem

Red triangle slugs are an important food source for birds, bats and lizards. 

Water dragon
Image: Water dragons are one of the animals that prey on red triangle slugs.

Red triangle slug anatomy

Red triangle slug
Image: Slugs are hermaphrodites. This means they are both male and female.

The head and mantle of a slug.
Image: Head and mantle

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 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 slugs 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.

Tail and foot of a red triangle slug
Image: Tail and foot

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.

Invertebrate explorer book
Image: Invertebrate explorer digital book

Find out more

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.

This book was designed by teachers to support the NSW Science and Technology K-6 syllabus and NSW English K-6 syllabus.

Content supports living world, Australian animals and class studies on invertebrates.

Download for free from Apple Books.

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