Ciliates (Phylum: Ciliophora)
The capacity to control motility in fine gradations and to swim in complex patterns is a decided advantage for aquatic organisms, especially for those that invade intricate spaces in search of food or pursue motile prey. The ciliates possess a marked vari
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General Morphology The capacity to control motility in fine gradations and to swim in complex patterns is a decided advantage for aquatic organisms, especially for those that invade intricate spaces in search of food or pursue motile prey. The ciliates possess a marked variety of motile systems based on ciliary motion. Thus, the organisms are able to move through the environment in search of prey often with remarkable agility and swiftness, or when sedentary, to create a flow of water carrying food to the organism. The arrangement of the hairlike organelles on the cell surface and the degree of coordinated action made possible by close proximity of the cilia varies considerably among groups. In some species, much of the cell surface is covered by rows of cilia (eg, Figure 6.1). These are called holotrichs, as the entire surface is usually rather uniformly ciliated. In other species, specialized groups of cilia are clustered at sites on the surface of the cell, either as somewhat loosely arranged tufts or organized into cirri (Figure 6.2c). A cirrus is a composite group of cilia (few to hundreds of cilia), often tapering toward the distal end and acting in unison. They typically are found in localized regions on the cell surface. When the cirri are largely localized on the ventral and anterior surfaces the ciliates are categorized as hypotrichs, signifying that the cirri are positioned beneath the cell. In other species, cilia are arranged in spirals (eg, in the spirotrichs) or in ribbonlike assemblages near the anterior (sometimes broader end) of the cell. Although many ciliates exhibit rapid and impressive locomotion, others such as the suctorians (eg, Figure 19.5) are sedentary and lack cilia during most of their life cycle. These feeding (trophont) stages are anchored to the substratum by a stalk or other form of holdfast. They snare prey on tentacles projecting from the cell surface. Ciliated stages occur during reproduction, and aid dispersal. While the cilia are clearly one of the distinctive features of the Ciliophora, the nuclei, rather than the cilia, provide the main distinguishing feature from other protozoa. There are two types of nuclei: (1) the macronucleus (one or more), regulating metabolism; and (2) small micronuclei, mediating sexual recombination and reproduction of the cell. The macronuclei arise by polyploidy from O. R. Anderson, Comparative Protozoology © Springer Science+Business Media New York 1988
General Morphology
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FIGURE 6.1. Comparative morphology of some common ciliates. (a) Tetrahymena patula, 80-160 J.1m; (b) Tetrahymena pyriformis, 40-60 J.1m; (c) Colpidium campylum, 50-70 J.1m; (d) Glaucoma scintillans, 45-73 J.1m; (e) Frontonia leucas, 150-600 J.1m; (f) Colpoda cucullus, 100 J.1m; (g) Loxodes rostrum, 125 J.1m; (h) Nassula aurea, 200-250 J.1m; (i) Paranassula microstoma, 80-95 J.1m; (j) Chilodonella cucullus, 130-150 J.1m. Symbols: c = buccal cavity, pog = post oral groove, wev = contractile vacuole, M = macronucleus, fv = food vacuole, pb = pharyngeal basket, arrow = Muller
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