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Annelids

Annelids

What are annelids?

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

Three earthworms on top of the soil
Image: Annelids do not have legs or a hard exoskeleton.

This group of invertebrates includes worms, leeches and polychaetes. There are more than 20,000 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.

Close up of a leach on the side of a tree
Image: Leeches move by stretching and contracting their body.

Case study - earthworms

Appearance 

Earthworms' bodies are made up of ring-like segments called annuli. These segments are covered in tiny hairs called setae which the earthworm 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.

An earthworm covered in some soil laying on a wood surface
Image: Earthworms can live for 4 to 8 years.

Habitat

Earthworms 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. 

Earthworm digging into soil
Image: Earthworms have small hairs on each segment that help them move through soil.

Diet

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

Leaf litter on the ground
Image: Earthworms will feed on decaying leaves in leaf litter.

Role in the ecosystem

Earthworms improve soil quality as they consume soil and then recycle organic matter through their waste 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 emerging from soil
Image: Earthworms are an important food source for many animals.

Earthworm anatomy

Earthworm drawing showing a segmented body with a belt-like clitellum around its neck
Image: The head of the earthworm is close to its clittelum.

Close up drawing of an earthworm’s head and belt-like clitellum around its neck
Image: Head and clitellum

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. 

Close up drawing of the segments of an earthworm
Image: Segments

Segments

Earthworms can 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.

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 free from Apple Books.

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