Ancient Cnidaria Fossil

The phylum Coelenterata, also known as Cnidaria, include the marine corals, sea fans, sea pens, sea anemones, hydra, and jellyfish. Hydra 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, their alternative phylum name) are used to capture, hold, and reel in prey as well as aiding in locomotion and defense.