Ancient Cnidaria Fossil

The phylum Coelenterata, also known as Cnidaria, includes the marine corals, sea fans, sea pens, sea anemones, hydras, and jellyfish. Hydras also have freshwater representatives and are the exception in the coelenterate taxon since they do not exhibit a medusa or "jellyfish" life stage. Specialized stinging cells known as nematocysts or cnidae (thus, the alternative phylum name) are used to capture, hold, and reel in prey, as well as to assist in locomotion and defense.