Source : Webster's Revised Unabridged Dictionary (1913)

Rostellum \Ros*tel"lum\, n.; pl. {Rostella}. [L. See {Rostel}.]
   A small beaklike process or extension of some part; a small
   rostrum; as, the rostellum of the stigma of violets, or of
   the operculum of many mosses; the rostellum on the head of a
   tapeworm.

Source : WordNet®

rostella
     See {rostellum}