water snail

from The Collaborative International Dictionary of English v.0.48

Water snail \Wa"ter snail`\
   1. (Zool.) Any aquatic pulmonate gastropod belonging to
      {Planorbis}, {Limnaea}, and allied genera; a pond snail.
      [1913 Webster]

   2. (Mech.) The Archimedean screw. [R.]
      [1913 Webster]