The Phylum Cnidaria contains three classes that differ depending on which phase of the life cycle, the polyp or medusa, is expressed. In general, the polyp form is anchored with tentacles pointing upward and the medusa form is free-floating with tentacles pointing downward. Stinging cells, or nematocysts, are characteristic of the Cnidarians. The three classes are:

• Class Hydrozoa-- the polyp phase is dominant and the medusa is reduced or absent from the life cycle. The symmetry is radial. This class includes the fire corals, hydroids, and siphonophores. One hydrozoan, Millepora, the fire coral, is included in this activity.
• Class Scyphozoa-- the medusa stage is dominant and polyps are rarely formed. This class is composed primarily of the jellyfishes.
• Class Anthozoa-- large, often elaborate polyps or colonies of polyps form. A medusa stage is never present. This class includes sea anemones, soft corals and stony corals. The Anthozoa, specifically the Zoantharia (stony corals), are the focus of this activity. 
  
  
  
• List of Corals Included
• Identification Key
• Unknowns from the NMITA database
• NMITA coral identification tool

Last updated on October 17, 1997-jlc.