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Kingdom protozoa and its 18 phyla

T Cavalier-Smith1

  • 1Department of Botany, University of British Columbia, Vancouver, Canada.

Microbiological Reviews
|December 1, 1993
PubMed
Summary

This study revises protist kingdom classification, removing Archezoa and refining Protozoa and Chromista based on phylogenetic data. The revised Protozoa are more homogeneous, distinguished from Chromista by specific cellular features.

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Area of Science:

  • Protistology and evolutionary biology.
  • Microbial taxonomy and systematics.
  • Phylogenetic classification of eukaryotes.

Background:

  • The classification of protist kingdoms has historically been complex and subject to revision.
  • Previous classifications did not fully reflect the phylogenetic relationships and cellular characteristics of protists.
  • The kingdom Archezoa was previously recognized but lacked key eukaryotic organelles.

Purpose of the Study:

  • To review and revise the classification of protist kingdoms, specifically Protozoa, Archezoa, and Chromista.
  • To establish a phylogenetic basis for the proposed classification down to the subclass level.
  • To delineate clear distinctions between the kingdoms Protozoa and Chromista.

Main Methods:

  • Review of existing protist kingdom demarcations and classifications.
  • Phylogenetic analysis to underpin the revised classification.
  • Detailed comparison of cellular structures, including mitochondria, peroxisomes, Golgi dictyosomes, and ciliary apparatus.

Main Results:

  • Archezoa are removed from classification due to their ancestral lack of mitochondria, peroxisomes, and Golgi dictyosomes.
  • The kingdom Protozoa is redefined as more homogeneous, characterized by the presence or secondary loss of mitochondria and peroxisomes, and predominantly phagotrophic nutrition.
  • A revised classification is provided, detailing subkingdoms, branches, infrakingdoms, and parvkingdoms within Protozoa, and distinguishing it from the photosynthetic kingdom Chromista based on specific ultrastructural and genetic features.

Conclusions:

  • The revised classification provides a more phylogenetically sound and homogeneous system for understanding protist diversity.
  • The removal of Archezoa simplifies the definition of Protozoa, emphasizing shared evolutionary history.
  • Clearer distinctions are established between Protozoa and Chromista, aiding in future research on these eukaryotic lineages.

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