Other invertebrates

Other invertebrate groups include:

  • annelids
  • nematodes
  • molluscs

Unlike arthropods, these invertebrates do not have jointed legs.


Annelids are segmented worms with soft bodies. Most of the worm’s body consists of identical segments, giving it a ‘ringed’ appearance.

Earthworms are annelids


Nematodes are tiny, thin worms without segments. Many species are free-living but others are parasites that cause disease. For example, hookworms can infect humans.

Light micrograph of a soil-dwelling bisexual nematode worm which feeds on bacteria
Caenorhabditis elegans is a free-living nematode about 1 mm long


Molluscs usually have a broad muscular foot and may also have a shell. Examples of molluscs include snails, slugs, squids and octopuses.

Clams in water
Clams are molluscs that live in the sea