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Paramecium is one of the best-known protists, often taught in school biology courses. It is a ciliate genus. Ciliates are a clade of protists which move by synchronous waves of tiny projections from their cuticle. These projections are called cilia (singular: cilium).[1][2] The species range from 50 to 350 μm in length.[3] They live in freshwater ponds, and eat bacteria, and other protists such as single-celled algae.

Paramecium species usually have bacterial symbionts, and some species have green algal symbionts.

Reproduction[change | change source]

Reproduction in Paramecium has been researched for many years. Paramecium has two nuclei (a large macronucleus and a single compact micronucleus).[4] They cannot survive without the macronucleus and cannot reproduce without the micronucleus.[1] Reproduction is either by binary fission (asexual), conjugation (sexual),[1] or, rarely, by endomixis, a process of self-fertilisation. During binary fission a fully grown organism divides into two daughter cells.[1] Conjugation consists of the temporary union of two organisms and the exchange of micro-nuclear elements.[1] Without the rejuvenating effects of conjugation a paramecium ages and dies.[1] Only opposite mating types, or genetically compatible organisms, can unite in conjugation.[1]

This reproductive system is unique to ciliates, and is one of the reasons why we think the Protista is not a natural clade (monophyletic), but rather a polyphyletic collection of single-celled organisms.

Paramecium aurelia[change | change source]

This species consists of 14 "syngens", each genetically isolated from every other, and biochemically unique. Each syngen has two mating types.[5] The syngens are so similar in appearance that they have not been given separate species names.[6]

References[change | change source]

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Paramacium
  2. 101 Paramecium caudatum
  3. A μm is a millioneth of a metre.
  4. Paramecium
  5. Sonneborn T.M. 1938. Mating types in Paramecium aurelia. Proc Am Philos Soc 79, 411-434.
  6. King R.C. Stansfield W.D. & Mulligan P.K. 2006. A dictionary of genetics, 7th ed. Oxford. p322