Class: Turbellaria (free-living flatworms)

Life > Eukaryotes > Opisthokonta > Metazoa (animals) > Bilateria > Lophotrochozoa > Platyhelminthes

Some 3000 species of turbellarian have been described. They are typically leaf-shaped worms and, although some may be 600 millimetres or more long, most are less than (often a lot less than) 10 millimetres. Most turbellarians are free living but Notoplana patellarum makes an interesting exception: it lives commensally in the mantle folds of the limpet, Patella oculus, found on rocky shores of the Western Cape.

The digestive system consists of a pharynx leading to a blind-ending gut. There is no anus, so the remains of any food that is ingested has to be ejected via the mouth. Turbellarians eat carrion or actively capture prey, which is swallowed whole or torn to pieces with the pharynx. In the gut, or gastrovascular cavity, endoderm cells engulf food particles by phagocytosis. The nervous system is not much advanced from the nerve net of cnidarians but there is a concentration of sensory cells and nervous tissue and the anterior end of the worm. Two nerve cords that run the length of the body.

They are hermaphroditic and generally reproduce sexually, although some species can also reproduce asexually by forming a “waist” and budding off the posterior part. This back end grows a new front and the original anterior end regenerates a new posterior part. Turbellarians normally move by means of cilia that cover the ventral surface; a few larger forms can swim by rhythmically throwing the edges of the body into folds.

Text © University of Cape Town Zoology staff