Both of these groups differ from the rest of the Metazoa in substantial ways. Unlike many multicellular animals, the bodies of these organisms are frequently not tightly integrated into a single functional unit. These animals are also frequently sessile as adults. The immature forms are often free-swimming larvae that settle onto a suitable substrate when they reach maturity.
All species have a 'worm' form.
There are both free-living and parasitic flatworms. The free living ones live in marine or fresh water or they inhabit terrestrial moist habitats. There are about 13,000 species of flatworms. Today we will examine preserved and live specimens of these organisms using the dissecting and compound microscope. We will observe their feeding behavior and compare their anatomical and structural features.