| Paramecium caudatum | |
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Scientific classification | |
| Domain: | Eukaryota |
| Clade: | Sar |
| Superphylum: | Alveolata |
| Phylum: | Ciliophora |
| Class: | Oligohymenophorea |
| Order: | Peniculida |
| Family: | Parameciidae |
| Genus: | Paramecium |
| Species: | P. caudatum |
| Binomial name | |
| Paramecium caudatum Ehrenberg, 1833 | |
Paramecium caudatum[1] is a species ofunicellularprotist in thephylumCiliophora.[2] They can reach 0.33 mm in length and are covered with minute hair-likeorganelles calledcilia.[3] The cilia are used in locomotion and feeding.[2] The species is very common, and widespread in marine, brackish and freshwater environments.[4][5]
Paramecium caudatum is 170–330 micrometres long (usually 200–300 micrometres).[6] The cell body is spindle-shaped, rounded at the front, tapering at theposterior to a blunt point. Early microscopists likened its shape to that of a slipper, and commonly referred to it as the "slipper animalcule."[7] Thepellicle is uniformly covered with cilia, and has a long oral groove, leading to deeply embedded oral cavity, lined with cilia (short, hair-like protoplasmic processes that serve as organs of locomotion and food capture).P. caudatum has twocontractile vacuoles, which serve to excrete excess water taken up from the outside, regulating the water contents of the body. Radially distributed "collecting canals" give the contractile vacuoles a distinctive star-like shape.[8][7] The cell is enclosed by a cellular envelope (cortex) densely studded with spindle-shapedextrusomes calledtrichocysts.[4][5]
P. caudatum feed onbacteria and smalleukaryotic cells, such asyeast andflagellatealgae.[2] the accumulated food particles, at the posterior end of the cytopharynx, are directed by the long cilia into the rounded, ball-like mass in the endoplasm called food vacuole. The food vacuoles are circulated by the streaming movement of the endoplasm which is called cyclosis. Inhypotonic conditions (freshwater), the cell absorbs water byosmosis. It regulates osmotic pressure with the help of bladder-like contractile vacuoles, gathering internal water through its star-shaped radial canals and expelling the excess through theplasma membrane.[3] When moving through the water, they follow a spiral path while rotating on the long axis.[2]
Paramecium caudatum has twonuclei (a large macronucleus and a single compact micronucleus).[9] As in other ciliates, individuals cannot survive without the macronucleus and cannot reproduce without the micronucleus.[3]Paramecia reproduce asexually, bybinary fission. During reproduction, the macronucleus splits by a type ofamitosis, and the micronuclei undergomitosis. The cell then divides transversally, and each new cell obtains a copy of the micronucleus and the macronucleus.[10]
Fission may occur as part of the normal vegetativecell cycle. Under certain conditions, it may be preceded by self-fertilization (autogamy),[11] or it may followconjugation, a sexual phenomenon in whichParamecia of compatible mating types fuse temporarily and exchange genetic material. During conjugation, the micronuclei of each conjugant divide bymeiosis and thehaploid gametes pass from one cell to the other. The gametes of each organism then fuse to formdiploid micronuclei. The old macronuclei are destroyed, and new ones are developed from the new micronuclei.[12]
Without the rejuvenating effects of autogamy or conjugation aParamecium ages and dies.[3] Only opposite mating types, or genetically compatible organisms, can unite in conjugation.[3]
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