Annelida and segmentation

The idea

Annelids have cylindrical bodies divided into segments, a body cavity and organ system level organisation; segmentation gives flexibility and precise control of movement, aided by muscles and a nerve cord.

An earthworm moves

An earthworm stretches and shortens as it moves through soil.

What feature of its body do you think helps it move so well?

• Its body is divided into segments
• It has a hard shell
• It has a hook and a sucker

Features of an annelid

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Segments help movement

Dividing the body into segments gives flexibility and finer control of movement. Muscles move the body and a nerve cord controls and coordinates it.

Annelids have cylindrical bodies divided into segments, a body cavity and organ system level organisation; segmentation gives flexibility and precise control of movement, aided by muscles and a nerve cord.

Notes

Annelids have segmented cylindrical bodies, a body cavity and organ systems; segmentation gives flexibility and precise control of movement, with muscles and a nerve cord.

Check yourself

Which animal is given as an example of an annelid?

What does segmentation give an annelid?

What helps annelids in locomotion?

What helps annelids in control and coordination?

• Hydra. Hydra is a cnidarian.
• Earthworm — correct. Yes!
• Starfish. The starfish is an echinoderm.
• A hard external skeleton. A hard external skeleton is a feature of arthropods.
• Pores for water flow. Pores for water flow are a feature of sponges.
• Greater flexibility and more precise control of movement — correct. Yes!
• Muscles — correct. Yes!
• A nerve cord. The nerve cord helps in control and coordination.
• Hooks and suckers. Hooks and suckers help parasitic flatworms attach to hosts.
• Muscles. Muscles help them in locomotion.
• A nerve cord — correct. Yes!
• Tentacles. Tentacles are used by cnidarians to capture prey.