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Eukaryote kingdoms: seven or nine?

T Cavalier-Smith

    Bio Systems
    |January 1, 1981
    PubMed
    Summary
    This summary is machine-generated.

    This study proposes a new nine-kingdom eukaryote classification based on cell structure, replacing older systems. This revised system offers a more accurate phylogenetic framework for understanding eukaryotic diversity.

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    Area of Science:

    • Eukaryote classification
    • Cell biology
    • Phylogenetics

    Background:

    • Classical two-kingdom and four-kingdom systems are inadequate for eukaryote classification.
    • Nutritional adaptive zones are poor criteria for primary taxa.
    • Fundamental cell structure provides a more robust basis for classification.

    Purpose of the Study:

    • To propose a new, more accurate classification system for eukaryotes.
    • To redefine eukaryotic kingdoms based on unique cell structural constellations.
    • To establish a monophyletic basis for primary eukaryotic taxa.

    Main Methods:

    • Analysis of mitochondrial cristae morphology (plate-like, disc-shaped, tubular).
    • Examination of Golgi cisternae structure (stacked vs. unstacked).

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  • Evaluation of ciliary structures (posterior vs. anterior, mastigonemes).
  • Assessment of plastid characteristics (envelope membranes, internal structure, chlorophyll types, starch presence).

    • Main Results:

    • A nine-kingdom system is proposed, each defined by unique cell structures.
    • Five kingdoms (Eufungi, Ciliofungi, Animalia, Biliphyta, Viridiplantae) possess plate-like mitochondrial cristae.
    • Euglenozoa (disc-shaped cristae), Cryptophyta (flattened tubular cristae), Chromophyta (tubular cristae), and Protozoa (tubular/vesicular cristae or absent mitochondria) form distinct kingdoms.
    • Kingdoms 4-9 share primitive anterior biciliation.

    Conclusions:

    • The proposed nine-kingdom system offers a more scientifically sound classification of eukaryotes.
    • This system provides a better phylogenetic framework than previous models.
    • A seven-kingdom compromise is suggested for general scientific use, with defined subkingdoms and applicable nomenclature codes.