The Collaborative International Dictionary of English v.0.48:

Paragnathus \Pa*rag"na*thus\ (p[.a]*r[a^]g"n[.a]*th[u^]s), n.;
   pl. Paragnathi (p[.a]*r[a^]g"n[.a]*th[imac]). [NL. See
   Para-, and Gnathic.] (Zool.)
   (a) One of the two lobes which form the lower lip, or
       metastome, of Crustacea.
   (b) One of the small, horny, toothlike jaws of certain
       annelids.
       [1913 Webster]