Turbellaria., a class of worm known as the Planarians (g.v.). They are classified as follows :-
1. RHABDOCOELIDA: small worms, with cylindrical or flat, bodies.
1. Acoela, primitive forms, without intestine, and usually without nervous system.
2. Rhabdocoela, forms with a straight intestine, e.g. the parasitic Anoplodium.
3. Alloiocoela, forms with a lobed intestine.
II. DENDROCOELIDA, large worms with branched intestines.
1. Tricladida, including the best known forms, Planaria, Bipalium, etc.
2. Polycladida, forms with a leaf-like body, e.g. Cotylea.