As the name suggests they have cilia for their mode of locomotion. They are free living and have aquatic habitat. They have pellicle covering and holozoic mode of nutrition. They show nuclear bi morphism that is macro and micro nucleus. Macronucleus control metabolic functions and is referred as vegetative nucleus. Micronucleus control reproductive functions and is the reproductive nucleus. Ingestion and egestion occur in different areas. Defense mechanism is provided by Trichocysts. They have contractile vacuoles. Reproduction occurs by sexual as well as asexual methods. Asexual methods include binary fission and budding. Conjugation is the sexual method of reproduction. Morphological and physiological variations occur along with the formation of cyst.
Paramecium is the ciliata organism known as slipper organism. It is an organism which feeds on surface. Bacteria are their source of food. Their shape is maintained by pellicle. Caudal tuft consists of bunch of cilia at the extreme posterior side. Feeding apparatus is constituted by peristome, vestibule, buccal cavity, cytosome and cyto pharynx. There is an opening near cytostome known as cytopyge. It is the excretory organ of paramecium through which undigested food passes. It consists of both macro and micro nucleus. Micro nucleuses are two in number while macro nucleus is one in number. It has contractile vacuoles which are two in number. They are surrounded by radial canals. These organelles provide osmoregulation. There are food vacuoles which act as a non contractile vacuole and help in digestion. Reproduction occurs by sexual as well as asexual methods. Asexual methods include transverse binary fission and budding. Conjugation, autogamy that is self fertilization, cytogamy includes features of both conjugation and autogamy, and hemixis are the sexual methods of reproduction. In hemixis macro nucleus is involved which breaks into many parts. Later some part may reunite to form macro nucleus and the remaining parts break down in endoplasm. This is referred as Purification act. Paramecium is of two types killer and sensitive. Killer consists of kappa particles along with DNA and RNA. They produce a poisonous substance paramecin. While the sensitive types have no kappa particles present in their structure.