A group of Stentors, large freshwater ciliates sometimes resembling water balloons, use cilia lining their mouths to pull themselves through water. Each possesses a macronucleus that appears as a string of beads. Other structures include food vacuoles and contractile vacuoles. Like many protozoa, Stentors have the ability to change shapes at will, and can range in form from pear shapes to trumpet shapes to spheres. Their bluish-green color comes from the pigment stentorin, which is found in many stentors. These protozoa can be found in lakes, ponds and streams throughout much of the world. Stentors typically range up to 1,000 microns in length. Recorded under Nomarski DIC.