Annelids fact sheet

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 long shiny earthworms lying on top of dark soil. Annelids do not have legs or a hard exoskeleton.

Fast facts – Annelids

What are they – Annelids are segmented worms from the phylum Annelida. Their bodies are made of ring-like segments, which is why their name comes from the Latin word annellus meaning “small ring”.

Body features – Annelids do not have legs or a hard exoskeleton.

Examples – This group includes worms, leeches and polychaetes (marine bristle worms). There are more than 20,000 annelid species worldwide.

Where they live – Found all around the world in oceans, freshwater, brackish water and soil.

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 striped leech attached to the side of a tree by one end. 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.

Earthworm partly covered in soil lying on a wooden surface. 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 with a pale band on its body burrowing down into moist soil. 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.

Layer of dead leaves, sticks and twigs forming leaf litter on the ground. 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 on the surface beginning to bury itself back into the soil. Earthworms are an important food source for many animals.

Earthworm anatomy

Head

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

Clitellum

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.

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.

Diagram of an earthworm showing its segmented body, saddle-like clitellum and head end near the clitellum. The clitellum of an earthworm is the saddle-like section. The head is close to its clitellum. The segments help the worm move.

More invertebrate fact sheets

Invertebrate fact sheets – overview
Earthworm fact sheet (single-species follow-up)
Myriapod fact sheet (many-segmented invertebrates like centipedes and millipedes)
Gastropod fact sheet (slugs and snails that also live in moist soil and leaf litter)

Habitats and ecosystems

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Annelids fact sheet

What are annelids?

Fast facts – Annelids