What structures and behaviors can be observed in planarians?
Planarians belong to the Turbellaria, the only free-living class in the phylum Platyhelminthes (flatworms). The term planarian encompasses all triclad turbellarians. An intestine that has three branches distinguishes the triclads. The brown planarian, Dugesia tigrina, has pigmented eye spots near the anterior end giving it a cross-eyed appearance. Planarians can regenerate significant portions of the body if cut into two or more pieces. Planarians move by gliding on the mucus they secrete. They prey on animals that become entangled in their mucus trail. Planarians are found in brooks, streams, ponds, and lakes. Planarians may be purchased through a science supply house or captured in the field. One method for collecting planarians is to place small chunks of fresh, raw liver on the bottom of a stream for pond near shore for a few hours. After retrieving the liver, flush specimens into a dish with a stream of water from a water bottle. Planarians have participated in NASA experiments in
