Includes anemones, zoanthids, corals, gorgonians, sea pens, sea whips, hydroids, sea firs, hydrocorals and a variety of forms casually called “jellyfish” or “jellies.”
Central to each cnidarian is a digestive system with one opening—yes, the mouth is also the anus! Ringing the opening is a circle of tentacles that have a definitive radial symmetry. The tentacles are festooned with millions of cells called cnidocytes, each of which has a tiny, harpoon-like mechanism. Prey capture is a common function of these specialized cells, many of which contain an associated toxin.
A cnidarian has one of two body types: the polyp or the medusa. The polyp, an example of which is shown in photograph A—rose anemone (CN8)—features a ring of tentacles and mouth/anus configuration atop a columnar body and exists either as a solitary entity or as part of a group with countless others.
In the case of sea anemones, these groups of polyps are clones, and members can be referred to as clone-mates. In the medusa body type, an example of which is shown in photograph B—sea nettle (CN91), a ring of tentacles and mouth/anus layout hang beneath a bell-shaped or pancake-shaped sac. This body form is usually free floating. Some cnidarian “rascals” have life cycles that alternate these two forms. More than 500 cnidarian species live in the Pacific Northwest.

Further Reading
Wrobel, David and Claudia Mills, 1998, Pacific Coast Pelagic Invertebrates, Monterey CA: Sea Challengers, 108 pp.