A planarian is a flatworm found in marine and freshwater, identified by its triangular head with two light-sensitive eyespots. Planaria have flat, tail-like bodies, with extendable pharynxes for sucking in food. Reproduction is hermaphroditic or by asexual splitting, or regeneration. Length: about 2.5 cm (1 in). Phylum Platyhelminthes; class Turbellaria; genera include Dugesia and Polycelis.