Platyhelminthes phylum includes flat worms which are bilaterally symmetrical, triploblastic and acoelomate, i.e. absent of true internal cavity or coelom. These animals can only be divided into two similar halves by their median longitudinal axis, thus their lateral side are mirror images of each other. These animals also have all three types of germ layer, i.e. ectoderm, mesoderm and endoderm. e.g. Taenia, liver fluke, etc.