Ciliata is a phylum of the subkingdom of protozoa.

The ciliates are single-celled organisms that have cilia, which are tiny hair-like structures that cover part or all of the cell surface. The cilia move in a coordinated way, driven by even tinier molecular motors that are called kinetosomes (natural nanomachines), thus providing ciliates with a means of moving around in their environment. Some of the cilia draw food into a mouth-like gullet through which the ciliate feeds.

Ciliates live wherever there is water, including moist soils as well as ponds, rivers, lakes and oceans. Different ciliates tolerate pollution to different degrees, so the presence or absence of certain ciliates is used as a measure of the degree of pollution in waters.

Structurally, the ciliates differ from other eukaryotes in having more than one nucleus. They have one large macronucleus and one or more micronuclei. The micronucleus contains DNA in the usual form of pairs of chromosomes. The DNA in the macronucleus, however, is just an unorganized mash of short pieces.

When the cell reproduces by asexual division, the micronuclei divide by mitosis in the usual way, but the macronucleus simply pulls itself apart into two pieces, an imperfect operation that leaves the animals defective after a few hundred generations. Ciliates also reproduce through sexual conjugation, in which the micronuclei split by meiosis and are exchanged. As part of sexual reproduction, the macronucleus is often regenerated by the micronucleus, which fixes the problem of generational weakening of the animals.

Cil`i*a"ta (?), n. pl. [NL. See Cilia.] Zool.

One of the orders of Infusoria, characterized by having cilia. In some species the cilia cover the body generally, in others they form a band around the mouth.

© Webster 1913.