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 are driven by tiny molecular motors that are called kinetosomes (natural nanomachines). The cilia move in a coordinated way that propels the organism around in its environment.

Some of the cilia draw food into a mouth-like gullet by which the animal feeds. Bacteria, algae, other small protists, rotting plant stuff serve as food. The ciia create a water current that pushes food into the ciliate cell as little bubbles called food vacuoles. The cell absorbs the food and turns it into energy to power the cell-machine and material for cell growth.

Ciliates live wherever there is water, including moist soils as well as puddles, ponds, rivers, lakes and oceans. Different ciliates tolerate pollution differently, so their presence or absence can serve as a measure of pollution in waters. The ones you are most likely to see when looking at pond water under a microscope are the stentor, the paramecium, and the vorticella.

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.

Domain: Eukarya
Kingdom: Protista
Subkingdom: Protozoa
Phylum: Ciliata (Ciliaphora)

Life & Ecology