Source : Webster's Revised Unabridged Dictionary (1913)

Dreissena \Dreis"se*na\, n. [NL. Named after Dreyssen, a Belgian
   physician.] (Zo["o]l.)
   A genus of bivalve shells of which one species ({D.
   polymorpha}) is often so abundant as to be very troublesome
   in the fresh waters of Europe.