E-Content : - 26 B.Sc Part 3(Zoology ), Paper 7 Topic: PARAMECIUM

Dr. S.K.Shitanshu (Guest Faculty) Deptt. Of Zoology T.N.B College , Bhagalpur T.M.B.U, Bhagalpur Email :- [email protected]

CLASSIFICATION

Phylum -- Protozoa Subphylum -- Ciliophora Class -- Ciliata Subclass -- Euciliata Order -- Holotricha Type -- P. caudatum Introduction

Paramecium is the commonest freshwater ciliate found in ditches, ponds, stream, lakes, rivers, etc. It is abundant in stagnant water containing decaying organic matter. The common species are P. caudatum, P. aurelia and P.bursaria.

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Structure P. caudatum is a microscopic ciliate about 180 to 300 long. The body is elongated slipper like and so it is also known as slipper animalcule. The body is asymmetrical with a flattened ventral surface and a convex dorsal surface. The anterior end is rounded and the posterior end is pointed. The body is covered with a thin elastic cuticular membrane called pellicle, which maintains characteristic shape of the paramecium. The pellicle, is not smooth but is provided with a large number of polygonal or hexagonal areas, each has an aperture in the centre through which a cilium projects out.

The entire body surface is covered by numerous hair like protoplasmic processes called cilia. A paramecium possesses about 10000 to 14000 cilia. All the cilia are equal size except a few large ones present at the posterior and forming caudal tuft and hence the specific name caudatum. Each cilium is 10-12 long , consists of an axial filament surrounded by a cytoplasmic sheath . Under electron microscope each cilium consists of 9 pairs of peripheral fibres and a pair of central fibres enclosed in a sheath . The cilia play important role in a locomotion and ingestion of food. The cytoplasm of the body is differentiated into an outer ectoplasm and an inner endoplasm.

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Ectoplasm It is the outer clear, narrow peripheral part of the cytoplasm. In the ectoplasm two important structures are present , which are : a. Basal granule or kinetosome. Each cilium originates from a small granule called basal granule or kinetosome. From each basal granule arises a fibril called kinetodesmos which runs anteriorly and meet with other fibril forming a bundle called kinetodesma. Each kinetodesma contains only 5 fibrils. The basal granuls and associated fibrils from intraciliary system which controls and co-ordinates the beating of cilia.

Vertical section through the ectoplasm b. Trichocyst These are spindle shaped organelles embeded in the ectoplasm alternating with basal granule. Each trichocyst opens to the exterior by a minute pore. The trichocyst consists of an elongated shaft and a terminal pointed tip called spike, covered by a cap. The

3 shaft is filled with a dense fluid having fibrous protein called trichinine. When the paramecium is stimulated, the trichocysts are discharged to the exterior as an elongated , fine thread on the body surface . The function of trichocyst is uncertain. Some believed that these serve as an organelle of adhesion, while other claim these to be defensive organelle. Endoplasm It is inner, granular semifluid part of the cytoplasm. It contains mitochondria, golgi body, reserve food materials etc. Important organelles of endoplasm are nuclear apparatus, contractile vacuoles and food vacuoles. Nuclear apparatus It consists of a large bean shaped macro or maganucleus situated near the cytostome and a small rounded micronucleus lodged in a depression of meganucleus.The macronucleus is the vegetative nucleus which controls the metabolic activity of the body while micronucleus regulates the reproductive activities of the organism.

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Contractile vacuoles

There are two large contractile vacuoles, one at each end of the body closed to the dorsal surface. Each contractile vacuole is surrounded by 6 to 10 narrow radiating canals. The posterior contractile vacuole pulsates faster than the anterior contractile vacuole. They play important role in osmoregulation.

Food vacuole There are numerous food vacuoles present in the endoplasm and these move with the streaming movement of endoplasm called cyclosis. The shape and size of the food vacuoles depend upon the nature of food. On the ventral surface of the paramecium there is a broad shallow oblique depression called oral groove which extends from the middle to the anterior end of the body. At the base of the oral groove there is an aperture called cystostome, from which arises a funnel like cytopharynx. The cilia of the cytopharynx are arranged in a special way . These cilia fused to form 3 membranelles , two penniculi and one quadrulus. Besides, there ia an endoral membrane just behind the cytostome , formed by the fusion of a row of cilia. All these constitute ingestory apparatus of paramecium . Near the posterior end of the body on the ventral side, there is a temporary opening called cytopyge which is visible only during egestion.

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