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  1. Karl J Aufderheide

Published Online: 15 NOV 2011

DOI: 10.1002/9780470015902.a0001969.pub3



How to Cite

Aufderheide, K. J. 2011. Paramecium. eLS. .

Author Information

  1. Texas A&M University, College Station, Texas, USA

Publication History

  1. Published Online: 15 NOV 2011


Members of the genus Paramecium (from the classical Greek, παραμηκησ, oblong or oval-shaped) are ciliated protozoa with an elongated shape (length approximately three to four times the width), a uniform distribution of cilia over the cell surface and a ciliated oral groove leading from the anterior of the cell to a midventral deep oral cavity. The oral apparatus is shaped like a funnel, with 12 rows of oral cilia in a helical array inside. Each cell has two distinct types of nuclei: one large, transcriptionally active, polycopy macronucleus and one or more small, transcriptionally inactive micronuclei. Many features make paramecia favourable organisms for the study of many cellular/developmental/genetic aspects of cells. Their large size allows microscopic observations as well as microinjections and cell surgery. They show Mendelian and non-Mendelian inheritance, and several different epigenetic inheritance patterns. The genome of Paramecium tetraurelia has been sequenced and is available for analysis.

Key Concepts:

  • Species of Paramecium are distributed worldwide in freshwater habitats and are easy to cultivate in the laboratory.

  • Morphological differences are not enough to distinguish some species of Paramecium.

  • The genomes of the macronucleus and micronucleus are not identical, even though both are derived from the same zygote nucleus.

  • The genome of Paramecium tetraurelia has been sequenced; 40 000 genes have been identified.

  • Paramecia do not use two of the three ‘stop codons’ for translation termination.

  • The trichocysts of paramecia are examples of a regulated exocytotic process.

  • The cortex of the cell contains the cilia, basal bodies and associated accessory structures.

  • Paramecia can carry a number of different types of endosymbiotic organisms.


  • ciliates;
  • macronucleus;
  • symbiosis;
  • DNA rearrangements;
  • codons