Tetrahymena are ciliate protozoa, common in aquatic habitats. They are pear-shaped and 30-100 μm in length, belonging among the hymenostomes and with cilia typical of that group. Tetrahymena thrive at temperatures of 18-22 degrees Celsius. Because of their short generation time and because they can be grown to high cell density in inexpensive media, they are common subjects of scientific study. Species include:

  • T. hegewischi
  • T. hyperangularis
  • T. malaccensis
  • T. pigmentosa
  • T. pyriformis
  • T. thermophila