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About 10 species of Paramecium have been discovered. Among them the common species are:
Common name: Slipper animalcule
It is a free-living freshwater protozoan. It is commonly found in pond, lake, ditches, river, rice fields where decomposed organic matter is abundant. It is omnivorous, mainly feed on bacteria or small unicellular algae and other small protozoans. It is mainly a surface feeder.
Shape and size:
It is a microscopic protozoan hardly seen by naked eyes as greyish spot. It is 170-290 µ long. It is 4 times as long as broad. Its body is clearly differentiated into rounded or blunt anterior end and conical or slightly pointed posterior end.
Its body is asymmetrical due to the presence of oral groove. So, its body also has 2 surfaces ventral or oral, dorsal or aboral.It is slipper shaped so commonly called as slipper animalcule.
It is a thin, tough and elastic membrane at coverslip body of Paramecium. It keeps the shape of paramecium always fixed. It is made up of gelatin. The surface of the pellicle is divided into a large number of hexagon area. Each cilium arises from the centre of each hexagonal area. Anterior and posterior sides of the hexagonal area contain a small opening for trichocyst i.e. trichocyst are discharged outside the body through these openings when necessary. The opening of trichocyst and cilium are alternate to each other.
They are the small hair-like projections distributed throughout the body. They are arranged uniformly in longitudinal rows. Such arrangement is called holotrichous. Each cilium is about 10µ long. However, cilia of the posterior end are quite longer called caudal tuft. Single Paramecium can contain 10,000- 14,000 cilia. Each cilium is made of small longitudinal fibrils which are arranged in the pattern of 9 + 2 i.e. 9 peripheral and 2 central. All these fibrils are externally covered by plasma membrane to form a single cilium. Cilia contains tubulin protein.
These are the organelles for locomotion and food capturing.
Oral groove (Peristome):
It is short, oblique pocket-like depression to derive food materials. It is situated on the ventral surface.
It is the funnel-shaped structure for collection and selection of food materials.
It is a small over aperture for ingestion of food material.
It is a short tube-like structure which guides food to the endoplasm.
Cytopyge/ cytoproct/ cell anus:
It is a small fixed opening present on the ventral surface just behind the cytopharynx. From this opening, undigested food materials are passed outside the body.