|Description of Stentor muelleri: Heterotrich ciliate, 500-1000 micrometres long, rarely up to 3 mm. Colorless, but may appear brownish in transmitted light. With zoochlorellae. Very contractile; slenderly trumpet-shaped when extended, with posterior drawn out into a thin stalk; plumply ovoid when contracted. Peristome wide with a domed central area. Often in loose, gelatinous tube. Macronucleus moniliform, with 10-20 beads. Common, widespread. Mainly in freshwater, but also in estuaries.