The Collaborative International Dictionary of English v.0.48:

Phylactocarp \Phy*lac"to*carp\, n. [Gr. fyla`ssein to guard +
   karpo`s fruit.] (Zool.)
   A branch of a plumularian hydroid specially modified in
   structure for the protection of the gonothec[ae].
   [1913 Webster] Phylactolaema