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Paramecium putrinum (=P. trichium) is a slipper shaped ciliate which is found in oxygenated aquatic environments feeding near vegetative matter. This organism is quite common and may easily be obtained from the shallow waters of the Connecticut River. It is the smallest of the paramecia, attaining lengths of 70-140 um. Despite its small size and stout build it is the most agile of the paramecia, capable of bending back on itself and contorting in ways which mimic fluid, ameboid movement.
Paramecia are unicellular microorganisms belonging to the protoctist phylum Ciliophora. Members of this phylum (ciliates) are characterized by their external covering of continuously beating, hair-like cilia. Cilia are motility organelles homologous to the undulating tails of sperm cells and the epithelial cilia which line our respiratory tracts. These single celled organisms must perform all of the same functions as a multicellular organism without the luxury of labor division amongst specialized cells, and it is their ability to fulfill these requirements along with their elaborate ultrastructure which places them among the most functionally complex cells.
Ciliates are exceptional among the eukaryotes (nucleated cells) since they possess one macronucleus and at least one micronucleus, whereas most eukaryotes have just one DNA containing nucleus. The macronucleus participates in the day to day activities of growth and reproduction while the micronucleus remains relatively dormant until the cell undergoes some type of sexual process. (Sex and reproduction are distinct processes and most organisms do not require sexual recombination of genetic material prior to reproduction.) This nuclear dualism imparts a unique twist on the inheritance patterns of these organisms in addition to providing a distinguishing characteristic which can be used for identification. Careful attention must be paid to physical structures since paramecia have been classified based on their microscopic morphology rather than their sexual compatibility.
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