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Description of Spirostomum minusHeterotrich ciliate, 300-800 x 30-40 microns, usually 400-600 microns. Very flexible and contractile. Shape slim to moderately broadly worm-form, approximately parallel-laterally, 10-20 times longer than broad. Anterior end of the cell rounded. Macronucleus as a chain of beads, consists of 8-50, usually 15-20 ellipsoidal beads which form a more or less long band, which lies in the median. Contractile vacuole at the rear end along the dorsal side. Under the cortex are many, spherical granules arranged in oblong bands to ever 3-4 rows. Cytoplasm transparent, colorless. About 20-30 spiral ciliary rows, with basal bodies in pairs. The adoral membranelle zone reaches from the front end to the body centre (about 35-50 % of the body length) and bends at its posteriod end to the right. With a creeping and winding movement or swims with rotation around the longitudinal axis.