The Collaborative International Dictionary of English v.0.48:

Sea anemone \Sea" a*nem"o*ne\ (Zool.)
   Any one of numerous species of soft-bodied Anthozoa,
   belonging to the order Actinaria; an actinian.
   [1913 Webster]

   Note: They have the oral disk surrounded by one or more
         circles of simple tapering tentacles, which are often
         very numerous, and when expanded somewhat resemble the
         petals of flowers, with colors varied and often very
         beautiful.
         [1913 Webster]

WordNet (r) 3.0 (2006):

sea anemone
    n 1: marine polyps that resemble flowers but have oral rings of
         tentacles; differ from corals in forming no hard skeleton
         [syn: sea anemone, anemone]