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Flatworms are the simplest of the worm groups. There are about 20,000 species in this group. They are found many places and can be free living or parasitic. A parasite lives off of another living thing called a host and can be harmful. One of the best known flatworms is the tapeworm. The tapeworm can get into a person's digestive tract and grow to enormous lengths. The tapeworm then eats off the host and is dangerous to the host as it grows and consumes more of the host and its food.
Flatworms are found in marine and fresh water.
|Muscular-Skeletal||A flatworm has no skeleton. It has tiny bristles called cilia that help it move as well as two layers of muscles under its skin. It has three cell layers called the endoderm, the mesoderm and the ectoderm. They also have the beginnings of a head region.|
|Digestion||A flatworm has a combination digestive/excretory system. It takes food in and gets rid of wastes through the same opening.|
|Nervous||A flatworm has a very simple nervous system with two nerve cords running down either side. It has two simple brains called ganglia, which are simple bundles of nerves. . It has two eyespots that help it sense light.|
|Circulation||A flatworm has a gastrovascular cavity with one opening. It eats small worms, insects and microscopic matter.|
|Respiration||A flatworm takes in oxygen, but has no formal respiratory system.|
|Reproduction||A flatworm reproduces by splitting in two. When a flatworm is split up it immediately forms a new flatworm.|
|Excretion||A flatworm gets rid of wastes through the same opening it takes in food.|
|Symmetry||A flatworm has bilateral symmetry.|
|Appearance||A flatworm can be microscopic or many feet long and is generally very thin.|
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