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Animals and Their Unicellular Ancestors

  1. Jordi Paps,
  2. Iñaki Ruiz-Trillo

Published Online: 18 OCT 2010

DOI: 10.1002/9780470015902.a0022853



How to Cite

Paps, J. and Ruiz-Trillo, I. 2010. Animals and Their Unicellular Ancestors. eLS. .

Author Information

  1. Universitat de Barcelona, Barcelona, Spain

Publication History

  1. Published Online: 18 OCT 2010


Animals belong to the Opisthokonta, one of the major divisions of the eukaryotic Tree of Life. This supergroup also includes other well-known groups such as fungi and choanoflagellates, in addition to some newly discovered unicellular taxa as the Ichthyosporea or the Filasterea. To unveil the origin of animal multicellularity, it is vital to understand the evolution of their single-celled relatives, as they might hold key genetic clues that might help us understand how the unicellular ancestors of animals became animals. Our current knowledge of unicellular animal relatives, their specific phylogenetic relationships and the role they might play in future research is being improved, thanks to molecular data.

Key Concepts:

  • Animals are members of the opisthokonts.

  • The Opisthokonta clade includes animals, fungi and several unicellular lineages.

  • Choanoflagellates are the closest animal unicellular relatives.

  • Ichthyosporea and Filasterea lineages are most closely related to animals than to fungi.

  • The opisthokonts include several multicellular types.

  • The opisthokont is a key evolutionary window to understand the unicellular to multicellular transition.


  • Opisthokonta;
  • multicellularity;
  • phylogeny;
  • evolution;
  • Metazoa;
  • Fungi;
  • choanoflagellates;
  • Ichthyosporea;
  • Filasterea