Paramecia are single-celled protists that are naturally found in aquatic habitats. They are typically oblong or slipper-shaped and are covered with short hairy structures called cilia. Certain paramecia are also easily cultured in labs and serve as useful model organisms.
Characteristics
Appearance
Paramecia cells are characteristically elongated. Historically, based on cell shape, these organisms were divided into two groups: aurelia and bursaria, according to the "The Biology of Paramecium, 2nd Ed." (Springer, 1986). The aurelia morphological type is oblong, or "cigar" shaped, with a somewhat tapered posterior end. Bursaria, on the other hand, represents cells that are "slipper" shaped. They tend to be shorter, and their posterior end is rounded.
Paramecia are a part of a group of organisms known as ciliates. As the name suggests, their bodies are covered in cilia, or short hairy protrusions. Cilia are essential for movement of paramecia. As these structures whip back and forth in an aquatic environment, they propel the organism through its surroundings. Paramecia can move forward at rates up to 2 millimeters per second, as José de Ondarza, an associate professor in the Department of Biological Sciences at SUNY Plattsburgh notes on his research website. Sometimes the organism will perform "avoidance reactions" by reversing the direction in which the cilia beat. This results in stopping, spinning or turning, after which point the paramecium resumes swimming forward. If multiple avoidance reactions follow one another, it is possible for a paramecium to swim backward, though not as smoothly as swimming forward.
Cilia also aid in feeding by pushing food into a rudimentary mouth opening known as the oral groove. Paramecia feed primarily on bacteria, but are known to eat yeast, unicellular algae and even some non-living substances such as milk powder, starch and powdered charcoal, according to "Biology of Paramecium.