List of animal phyla
Platyhelminthes: the flatworms. Classes: Turbellaria: free-living and aquatic (4,500 species); Trematoda: parasitic flukes of molluscs and vertebrates (~1500 species); Cestoda: tapeworms, parasitic in the digestive tract of vertebrates (3400 species); Monogenea: ectoparasites on the gills and skin of fish (1100 species). Müller's larva is characteristic of the free-living species, but in the parasitic groups development may be direct.