Planaria
Planaria are free-living flatworms that live in quiet ponds or bodies of water. In some areas you can even catch a few planarian by attaching a piece of liver to a fish hook and a sinker and dropping it into the water. Wait a few minutes and pull the liver out and you may find tiny little black worms feasting on the meat. Like all flatworms, planaria belong to the Kingdom Animalia, and the Phylum Platyhelminthes. This phylum also contains parasitic flatworms, like the tapeworm and the liver fluke.The body, when elongated, is soft, leaf-shaped, and ciliated. The spade-shaped head has two eyes and sometimes tentacles. The tail is pointed. The mouth is on the ventral, or lower, side, often more than half-way toward the tail. A body cavity, or coelom, is absent. The pharynx, which may be protruded from the mouth, ends in an intestine that is usually blind.
The digestive system
•Eating - scavenging dead matter through pharynx located at center of underside.
•Digestion and circulation - The planarian has a gastrovascular cavity in which digestion occurs.
-The food enters the gastrovascular cavity through the pharynx located at the center of the planarian's underside and is digested into feces and monomers.
-The feces exit through the pharynx and the monomers are absorbed by the tissues from the gastrovascular cavity. The gastrovascular cavity is multiply-branched and so virtually all cells are near one of the branches. Not a true circulatory system - no blood or blood vessels.
•Excretion - Since the planarian's body is so thin, the oxygen and carbon dioxide exchange occurs by diffusion through its skin.
•The liquid waste is collected by unique specialized 'flame cells' and excreted through pores in the epidermis.
•Digestion and circulation - The planarian has a gastrovascular cavity in which digestion occurs.
-The food enters the gastrovascular cavity through the pharynx located at the center of the planarian's underside and is digested into feces and monomers.
-The feces exit through the pharynx and the monomers are absorbed by the tissues from the gastrovascular cavity. The gastrovascular cavity is multiply-branched and so virtually all cells are near one of the branches. Not a true circulatory system - no blood or blood vessels.
•Excretion - Since the planarian's body is so thin, the oxygen and carbon dioxide exchange occurs by diffusion through its skin.
•The liquid waste is collected by unique specialized 'flame cells' and excreted through pores in the epidermis.