The Collaborative International Dictionary of English v.0.48:

Glass-sponge \Glass"-sponge`\, n. (Zool.)
   A siliceous sponge, of the genus Hyalonema, and allied
   genera; -- so called from their glassy fibers or spicules; --
   called also vitreous sponge. See Glass-rope, and
   Euplectella.
   [1913 Webster]