The Collaborative International Dictionary of English v.0.48:

Polyneme \Pol"y*neme\, n. [Poly- + Gr. ? thread.] (Zool.)
   Any one of numerous species of tropical food fishes of the
   family Polynemid[ae]. They have several slender filaments,
   often very long, below the pectoral fin. Some of them yield
   isinglass of good quality. Called also threadfish.
   [1913 Webster]