Flatworms are the simplest of the worm groups. There are about 20,000 species in this group. Flatworms are found many places and can be free living or parasitic. A parasite lives off another living thing called a host and can be harmful. One of the best known flatworms is the tapeworm. Find out more!

Flatworms are bilaterally symmetrical and dorsoventrally flattened meaning ‘they look like a ribbon’. Their bodies have 3 layers of tissues with organs and organelles however, they contain no internal cavity.

Flatworms possess a ‘blind gut’, they have a mouth but no opening at the lower end of the alimentary canal through which solid waste is eliminated from the body. Instead, they have what are called ‘Protonephridial excretory organs’.

They reproduce as hermaphrodites. Most species occur in all major habitats and are parasites of other animals feeding mostly on small animals and other smaller life forms.

Also, they are found in marine and fresh water. Flatworms are not related to sea slugs or other molluscs. Although very thin and delicate, flatworms are active carnivores and scavengers, using their proboscis to feed on dead or injured animals and colonial animals such as bryozoans and soft-corals.

Flatworms can quickly glide along the bottom by using the fine hairlike cilia which cover their body. When disturbed they can swim for a considerable period of time by throwing the sides of their body into undulating waves.