Class: Turbellaria (free-living flatworms)
Metazoa (animals) > Bilateria > Lophotrochozoa >
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.