Spirostomum (Protozoan) Videos

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Some of the largest ciliates belong to the genus Spirostomum, some species large enough to see with the naked eye. These organisms hold the record for the fastest body contractions of any living cell, contracting its length to 25% of its normal size in 6-8 milliseconds. Spirostomum feeds on bacteria and during cold weather forms large clusters of organisms that hibernate together.

Spirostomum belongs to the class Spirotrichea in the phylum Ciliophora; the ciliates, of which there are approximately 8,000 species, are generally considered to be the most evolved and complex of the protozoans. The cell surface is covered with hundreds of hairlike structures called cilia that are arranged in rows. The cilia beat in synchronized waves, propelling the organism through the water. Most ciliates possess an oral cavity, or cytostome, through which food enters the cell. In some ciliates, the cilia around the cytostome have become modified into sheets called membranelles, which create a feeding current and act as a sieve to trap food particles. Ciliates possess two types of nuclei, a large nucleus, or macronucleus, and one or more small nuclei, or micronuclei. Reproduction is primarily asexual, by binary fission, but sexual reproduction also occurs by conjugation, a process by which two organisms exchange nuclear material.