Flatworms have a cephalized nervous system that consists of head ganglion, usually attached to longitudinal nerve cords that are interconnected across the body by transverse branches. Movement in some flatworms is controlled by longitudinal, circular, and oblique layers of muscle. Others move along slime trails by the beating of epidermal cilia. The development of directional movement is correlated with cephalization. In some flatworms, the process of cephalization has included the development in the head region of light-sensitive organs called ocelli.
Most flatworms can reproduce sexually or asexually.
Most are monoecious. Most of these have developed ways of avoiding self-fertilization. Flatworms include a large number of parasitic forms, some of which are extremely damaging to human populations. Animal Diversity . Brusca, R. C., and G. J. Brusca.