Hammerhead Worm (Bipalium vagum)
by Ben Blocker
Dugesia sp. but most likely D. tigrina. Now named Girardia per EOL.org. Found on rocks in slow moving stream. Photo taken while specimens were feeding on a mayfly larva.
The flatworms, known in scientific literature as Platyhelminthes or Plathelminthes (from the Greek πλατύ, platy, meaning "flat" and ἕλμινς (root: ἑλμινθ-), helminth-, meaning worm) are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals. Unlike other bilaterians, they have no body cavity, and no specialized circulatory and respiratory organs, which restricts them to having flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion. The digestive cavity has only one opening...