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| Paramecia are a group of unicellular ciliate
protozoa formerly known as slipper animalcules from their slipper shape.
They are commonly studied as a representative of the ciliate group. Paramecia
range from about 50 to 350 µm in length, depending on species. Simple
cilia cover the body which allow the cell to move with a synchronous motion.
There is also a deep oral groove containing inconspicuous compound oral
cilia (as found in other peniculids) that is used to draw food inside.
They generally feed upon bacteria and other small cells. Osmoregulation
is carried out by a pair of contractile vacuoles, which actively expel
water absorbed by osmosis from their surroundings.
Paramecia are widespread in freshwater environments, and are especially common in scums. Paramecia are attracted by acidic conditions. Certain single-celled eukaryotes, such as Paramecium, are examples for exceptions to the universality of the genetic code. The paramecium is a prolate spheroid, rounded at the front and pointed at the back. The pellicle is a stiff but elastic membrane that gives the paramecium its definite shape. Covering the pellicle are many tiny hairs, called cilia. On the side beginning near the front end and continuing down half way is the oral groove, which collects food until it is swept into the cell mouth. There is an opening near the back end called the anal pore. The contractile vacuole and the radiating canals are also found on the outside of a paramecium.
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