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Luanco, Principado de Asturias, Espaa
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Sant Marti Sarroca, Catalonia, Spain
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Ribadelago de Franco, Castille and Leon, Spain
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Portrait of Spirostomum minus, a large heterotrich ciliate. Synonymous with S. intermedium. S. minus is very similar in overall appearance to S. ambiguum but is shorter in length (300-800 microns; this individual is 537 microns long). S. ambiguum is commonly 1000-4000 microns long. Also the peristome occupies about 50% of the body length in S. minus and about 75% of the body length in S. ambiguum. The body is vermiform, cylindrical and highly contractile. Somatic kineties are longitudinal and uniform. The long adoral zone of membranelles is seen along the ventral surface. The macronucleus (seen well here) is moniliform in both. There is a posterior contractile vacuole with a long dorsal collecting canal. From organically enriched standing fresh water near Boise, Idaho. DIC optics.
