Stentor: A Heterotrich Ciliate.
This is a Stentor, one of the largest of the commonly encountered freshwater protozoans.
The actively feeding mouth end of the extended organism is seen, with the cirri (1) stopped in their metachronal rhythm by the electronic flash which was used to take the picture.
The large relatively clear circular space (2) below the fringe of cirri is a contractile vacuole, through which the cirri on the other side of the peristomal area can be seen. The circular outline of a food vacuole (3) is also seen. The body is covered with rows of fine cilia, not imaged in this picture.
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