Paramecium caudatum

Paramecium caudatum are unicellular organisms belonging to the genus of protozoa of the phylum Ciliophora. They are less than 0.25mm in length and covered with minute hair-like projections called cilia The cilia are used in locomotion and during feeding. They are often called slipper animalcules because of their slipper-like shape.

They feed on bacteria which are driven into the gullet by the cilia. Their natural habitat is fresh water. They take in water by osmosis from the hypotonic environment, bladder-like contractile vacuoles accumulate the excess water from radial canals and periodically expel it through the plasma membrane by contractions of the surrounding cytoplasm. The contractile vacuoles also serve to maintain osmotic pressure. When moving through the water, they follow a spiral path while rotating on the long axis. When a they encounter an obstacle, they exhibits the so-called avoidance reaction; it backs away at an angle and starts off in a new direction.

Paramecium have 2 nuclei (a large macronucleus and a single compact micronucleus). They cannot survive without macro-nucleus and cannot reproduce without micro-nucleus. Reproduction is either by asexual binary fission or occasionally by conjugation (sexual) and rarely by endomixis, a process involving total nuclear reorganization of individual organisms. During binary fission a fully grown organism divides into two daughter cells. Conjugation consists of the temporary union of 2 organisms and the exchange of micro-nuclear elements. Without the rejuvenating effects of conjugation a paramecium ages and dies. Only opposite mating types, or genetically compatible organisms, can unite in conjugation.