Phylum Cnidaria includes classes hydrozoa and scyphozoa.  Like all cnidarians, hydrozoans and scyphozoans are animals that have tentacles which have cnidocytes.  Hydrozoans include hydra, obelia, and portuguese man-o-war.   Most members of hydrozoa include both the polyp and medusa stage.

     Class scyphozoa includes jellyfish.  The medusa is the most prominent form; the polyp is restricted to the small larval stage.
 

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6.	7. Obelia	8. Portuguese  man-o-war	9.	10. jellyfish