The Collaborative International Dictionary of English v.0.48:

ameba \ameba\ n.
   1. 1 naked freshwater or marine or parasitic protozoa that
      form temporary pseudopods for feeding and locomotion. Same
      as amoeba.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

ameba
    n 1: naked freshwater or marine or parasitic protozoa that form
         temporary pseudopods for feeding and locomotion [syn:
         ameba, amoeba]