Paramecium caudatum

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Paramecium

Phylum:	Ciliophora
Order:	Hymenostomatida
Family:	Paramecidae
Genus:	Paramecium
Species:	P. caudatum

Binomial name

Paramecium caudatum
Ehr.

Paramecium caudatum ^[1] are unicellular organisms belonging to the genus of paramecium of the phylum Ciliophora^[2]. They are less than 0.25mm in length and are covered with minute hair-like projections called cilia^[3]. The cilia are used in locomotion and feeding^[2]. They are often called slipper animalcules because of their slipper-like shape^[2].

P. caudatum feed on bacteria by driving them into the gullet with cilia^[2]. Their natural habitat is fresh water^[3]. They take in water from the hypotonic environment via osmosis and use bladder-like contractile vacuoles to accumulate excess water from radial canals and periodically expel it through the plasma membrane by contractions of the surrounding cytoplasm^[3]. The contractile vacuoles also serve to maintain osmotic pressure^[2]. When moving through the water, they follow a spiral path while rotating on the long axis^[2]. When they encounter an obstacle, they exhibit the so-called "avoidance reaction"; they back away at an angle and start off in a new direction^[2].

Paramecium have 2 nuclei (a large macronucleus and a single compact micronucleus)^[4]. They cannot survive without the macronucleus and cannot reproduce without the micro-nucleus^[3]. Reproduction is either accomplished by binary fission (asexual), conjugation (sexual)^[3], or (rarely) by endomixis, a process involving total nuclear reorganization of individual organisms^[2]. During binary fission a fully grown organism divides into two daughter cells^[3]. Conjugation consists of the temporary union of 2 organisms and the exchange of micro-nuclear elements^[3]. Without the rejuvenating effects of conjugation a paramecium ages and dies^[3]. Only opposite mating types, or genetically compatible organisms, can unite in conjugation^[3].