There are no ganglia in any of the classes of flatworms, but two photoreceptors are present on most worms. They also have longitudinal nerve cords present. Respiration Because of their flat bodies, flatworms have a large surface area to volume ratio, allowing them to breathe by diffusion through the skin. Classification Flatworms are divided into three groups, the Turbellaria, which are free living worms, Dugesia, which live in water or moist soil of all kinds, and Trematoda, which is a group made up entirely of parasites, including the fluke, a parasite found in humans. Flatworm Notes Flatworms are much more complex that sponges or jellyfish and more animal-like.
Flatworms have a nervous, digestive and reproductive systems.
Flatworms are bilaterally symmetric. This means they have identical left and right halves as in humans. Flatworms have brains. Platyhelminthes are the flatworms. Flatworms include tapeworms, flukes, planaria and their allies.