The Collaborative International Dictionary of English v.0.48:

Hydranth \Hy"dranth\, n. [Hydra + Gr. ? a flower.] (Zool.)
   One of the nutritive zooids of a hydroid colony. Also applied
   to the proboscis or manubrium of a hydroid medusa. See
   Illust. of Hydroidea.
   [1913 Webster]