BugWise

We will focus on land living invertebrates that can be categorised into three broad groups:

Worms

An example of an earthworm. Photo: R Mascord © Australian Museum.

• The most familiar worms are the roundworms, the flatworms and the segmented worms.
• Worms are generally cylindrical or flat-like.
• Worms have a fluid-filled body surrounded by muscle and a tough skin (hydrostatic skeleton).
• Worms move by constricting muscles and redistributing internal fluids.

Molluscs

An example of a snail. Photo: © D Nelson.

• On land molluscs are represented by snails and slugs.
• Snails and slugs have various body shapes.
• Snails and slugs have a fluid filled body surrounded by a muscular body. Generally they secrete a hardened shell, which protects the body from fluid loss.
• The shell may take on many different shapes depending on the species.

Arthropods

This true bug (Tylocryptus egenus) looks like a stick. Photo: M Bulbert © Australian Museum.

• Arthropods are incredibly diverse they account for more than 75% of all animal species.
• Arthropod groups include the insects, the arachnids (spiders and relatives), the crustaceans (e.g. slaters, land crabs), and the Myriapods (centipedes and millipedes).
• Arthropods have a body encased by a rigid substance called chitin (exoskeleton). The exoskeleton is likened to a suit of armour, and like armour has many joints to allow a wide range of movements.

Of the arthropods, 80% are made up of the insects. Insects are considered to the most numerous and diverse of all the animals on earth. Within insects there are around 30 broad groups that include many familiar invertebrates such as beetles, butterflies, cicadas, flies, bees and fleas.

Insects are the only invertebrates to master flight and they have a remarkable range of body shapes. Ranging from dome shapes to long stick-like bodies. They may also appear like many natural features such as a leaf or a rock and in some cases they may even look like other animals (called animal mimicry).