The phylum Platyhelminthes consists of simple worm-like animals called flatworms. Flatworms live on land, in fresh water, in the ocean, and in or on other animals as parasites (e.g., tapeworms).
Flatworms are more complex than cnidarians. Cnidarians have two layers of cells, the ectoderm and the endoderm; flatworms have a middle layer called the mesoderm between the other two layers.
latworms have a digestive system with only a single opening into the digestive cavity, these flatworms feed through a pharynx. A pharynx is a long, tubular mouthpart that extends from the body.
Flatworms have a surprisingly elaborate system to rid the body of wastes. his network runs the length of the animal on each side and opens to the outside through small pores in the posterior region of the body. Connected to the tubes are tiny cells that move wastes and water from the tissues into the tubes. These cells contain flagella that beat back and forth, creating a current of fluid that constantly moves toward the excretory pores. Under a microscope the flagellar movement looks like a flickering fire, and the structure is called a flame bulb.
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