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What are annelids?

Annelids are segmented worms. They are characterised by the ring-like segments around their body. The term annelid comes from the Latin word for ‘little ring’. Annelids are found worldwide in the ocean, in freshwater, in brackish water and in the soil.

This group of invertebrates includes worms, leeches and polychaetes. There are around 9000 species of annelids in the world. Annelids can vary in length from 0.8 millimetres to 3 metres as is the case of the giant Gippsland earthworm.

Case study - worms


Worms' bodies are made up of ring-like segments called annuli. These segments are covered in tiny hairs which the worm uses when moving and burrowing. They have an outer muscular body wall surrounding a digestive tract that begins with the mouth in the first segment.


Worms live in soil and moist leaf litter. During the day they often burrow close to the surface. Earthworms can dig burrows as deep as 2 metres. 


Mainly feeding at night, worms consume soil and decomposing organic matter from plants.

Role in the ecosystem

Worms improve soil quality as they recycle organic matter which makes nutrients and minerals for plants to use. They also aerate the soil and allow for water infiltration as they move and burrow through the soil. Worms are also part of the food chain providing food for birds, reptiles and invertebrates. 

Earthworm anatomy

Head and clitellum

The head of the worm contains the mouth. It also has light and chemical sensitive organs to sense the surrounding environment.

The clitellum is sometimes called a saddle. The clitellum contains the gland cells. These cells are used to create a cocoon or egg that holds the worm embryos. 


Earthworms have between 100 to 150 segments. Each segment contains muscles that help the worm to move.

Each segment has bristle-like hairs called setae which grip the soil to help with movement.

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 free from Apple Books.

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