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.
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.
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.
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.
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.
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.
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.
The clitellum of an earthworm is the saddle-like section. The head is close to its clitellum. The segments help the worm move.
Invertebrate explorer digital book
Find out more
Written by teachers, 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.
Content supports living things, Australian animals and class studies on invertebrates.