What is Planaria?
{{italictitle}} {{Taxobox | name = ''Planaria'' | image = Planaria Geoplanidae, 3 cm (02).JPG | image_width = 240px | image_caption = | regnum = [[Animalia]] | phylum = [[Platyhelminthes]] | classis = [[Turbellaria]] | ordo = Tricladida | familia = Planariidae | genus = '''Planaria''' | genus_authority = Müller OF, 1776}} '''''Planaria''''' is a small aquatic [[genus]] of [[flatworm]]. The term is also used for other similar flatworms. They are fresh water animals which move in a smooth wave-like manner. Planaria are free-living. They can live in fresh water or very damp soil, depending on the type. ''Planaria'' are [[hermaphrodite]]: they produce both [[Ovum|eggs]] and [[sperm]]. To reproduce, a planarian releases eggs and sperm into the water, where the eggs get fertilized. Planaria can repair damage by [[Regeneration|regenerating]] any part of their body. ''Planaria'' are the one of most simple creatures to develop a nervous system. Their nervous system consists of [[ganglia]] under the [[eyespot]]s and a cord of nerves that run down the body, under the [[gut]] (ventral nerve cord). The three pairs of ganglia under the eyespots make a inverted U shape that have nerves sticking out to the outside of the head so that the head of the planarian is more sensitive than the rest of the body. If the light hits the animal near the eyespots, they usually move away into darker water. The digestive system of ''Planaria'' consist of a mouth a pharynx and a gut cavity. Its mouth is on the underside of the body. Digestive [[enzyme]]s are released from the mouth onto the food to soften it, Then the half digested food is sucked up the pharynx and into the stomach. From there the [[nutrient]]s diffuse into the rest of the body. There are no circulatory or [[respiratory system]]s. Oxygen enters and [[carbon dioxide]] leaves the planarian's body by diffusing through the body wall. ''Planaria'' do not have a [[skeleton]]. They have an extendable crumpled muscle that allows them to move. Also, planarians have three l