Paramecium - The Slipper Organisms or Slipper Animalcule
Paramecium is a free-living ciliate which is found in fresh water ponds, pools, ditches, rice fields and slow streams having decaying matter. It is abundant in water which has plenty of bacteria. Most widely distributed species are Paramecium caudatum and paramecium Aurelia.
Nutrition is holozoic. Bacteria are its chief food. Paramecium is a surface feeder. It swims actively with the help of cilia. Exchange of gases takes place through body surface (pellicle) Both asexual (e.g., transverse binary fission) and sexual reproduction (e.g., conjugation) are found in paramecium. In conjugation, there is a mutual exchange of pronuclei and their fusion. General characters of Paramecium are:
Shape, size and colour: Paramecium caudatum is called "slipper animalcule". Its anterior end is bluntly rounded while the posterior end is conical and pointed.
Pellicle: It is a thin flexible and living membrane which maintains its shape.
The cytoplasm is differentiated into outer ecotoplasm and inner endoplasm.
Cilia: Numerous cilia are distributed over the body surface. The cilia of the extreme posterior end are longer and form a bunch called caudal tuft. Cilia are for locomotion , food capture and are also tactile in function (respond to touch).
Trichocysts: These are fusiform bodies which are found in the ecotoplasm just below the pellicular. When a trichocyst is discharged, its shoots out at body surface trough the pellicles pores in the form of a long needle-like thread . The discharged trichocyst serve for anchoring defence , or it may be a reaction to injury.
Feeding Apparatus: It consists of a shallow and wide peristome (= oral groove) , a funnel-like vestibule, somewhat S-shaped buccal cavity which opens through a cytostome (= cell mouth), into a short cytopharynx. The latter ends in the endoplasm.
A temporary opening is called cytopyge (= cytoproct or cell anus), is present a little behind the cytostome. Undigested food is passed through cytopyge.
Nuclei: Paramecium caudatum contains a single large macronucleus (= meganucleus) and one small micronucleus. Paramecium Aurelia has one mega nucleus and two micronuclei. The micronucleus controls metabolism such as, feeding and maintenance, whereas the micronucleus takes an important role in reproduction. When two types of nuclei are present, it is called nuclear dimorphism.
Contractile Vacuoles and Radial Canals: Paramecium contains two contractile vacuoles which have fixed position. One contractile vacuole is present near the anterior and while another contractile vacuole is found towards posterior end of the body. Each contractile vacuole is surrounded by 5 to 12 radial canals (feeding canals). Excess of water is transferred from the cytoplasm to the radial canals. The latter pour water into the contractile vacuole. The contractile vacuole expels water outside the body. Thus the contractile vacuoles and radial canals are for osmoregulation. The anterior and posterior contractile vacuole contract alternately.
Food Vacuoles : Several non contractile food vacuoles (= gastrioles) are seen moving along definite course (cyclosis) within the sreaming endoplasm. Each food vacuole consists of a definite vacuolar membrane and food particles. The food vacuoles are meant for intracellular digestion.
Other Cell Organelles and Cytoplasmic inclusions: The cytoplasm also contains mitochondria, Golgi complex, Ribosomes, crystals, reserve food granules (i.e., lipid granules), etc.
Two types of paramecia reported
- Killer Paramecia: They contain Kappa particles. The latter have DNA and RNA. A killer paramecium may contains hundreds of Kappa Particles. Killer paramecium produces a poisonous substance, called paramecin which kills sensitive paramecia.
- Sensitive paramecia: They do not contains Kappa Particles and hence do not secrete paramecin.
Cyst formation may occur in paramecium.
Balantidium coli is a ciliate protozoan parasite in colon a caecum of man. Balantidium causes 'Balantidial dysentery or Balantidiasis'. Balantidium is Monogenetic, has only one host. Encystment takes place in Balantidium coli. Infection os oral through contaminated food and water.