The Collaborative International Dictionary of English v.0.48:

Nematocalyx \Nem`a*to*ca"lyx\, n.; pl. Nematocalyces, E.
   Nematocalyxes. [NL. See Nemato-, and Calyx.] (Zool.)
   One of a peculiar kind of cups, or calicles, found upon
   hydroids of the family Plumularidae. They contain
   nematocysts. See Plumularia.
   [1913 Webster]