∞ generated and posted on 2016.09.03 ∞

Members of animal phylum Platyhelminthes.

Flatworms are triploblastic. This is unlike the diploblastic cnidarians. Like the cnidarians, however, flatworms possess only single opening to what is known as their gastrovascular cavity. Flatworms, unlike many other animals, lack a coelom, that is, a body cavity (the gastrovascular cavity, by contrast, technically is not a body cavity but instead a volume that is open to the outside world).

Though numerous free-living flatworms exist, most prominently the beautiful marine flatworms, a number of parasitic forms exist as well including tapeworms and also what are known as flukes. The latter are the cause of the disease schistosomiasis or (perhaps confusingly) snail fever (confusing since snails are not flatworms but instead serve as intermediate hosts for flukes).