CAVALIER - SMITH’s EIGHT KINGDOM CLASSIFICATION (Cavalier - Smith’s Six Kingdom Model and Cavalier - Smith’s Seven Kingdom Model)

CAVALIER - SMITH’s EIGHT KINGDOM CLASSIFICATION

·       The Kingdom Protista was still too diverse to be taxonomically useful. Many attempts have been made to divide Protists into better-defined kingdoms and in this regard, an eight-kingdom system was given by Thomas Cavalier-Smith in 1987.

·       In 1981, before proposing Eight Kingdom Classification, Cavalier-Smith had divided all the eukaryotes into Seven Kingdoms. In it, he created Chromista for a separate Kingdom of some Protists.

·      Cavalier-Smith gave the Eight kingdom system of classification by revising Whittaker's Five Kingdoms of Classification.

·    Using ultrastructural characteristics as well as rRNA sequences, Cavalier-Smith divides all organisms into 2 Empires and 8 Kingdoms.

ü  2 Empires

a)     Empire Bacteria

§  Kingdom Eubacteria

§  Kingdom Archaeobacteria

b)     Empire Eukaryota

§  Kingdom Archezoa (Protists lacking Mitochondria)

§  Kingdom Protozoa

§  Kingdom Chromista (Protists whose Plastids contain Chlorophyll c)

§  Kingdom Fungi

§  Kingdom Plantae

§  Kingdom Animalia

·       Archezoa and Chromista are the two new Kingdoms of Eukaryotes.

Kingdom Archezoa

·  The Kingdom Archezoa (Amitochondriate eukaryotes) consists of primitive eukaryotic unicellular microorganisms (e.g. Giardia) that possess 70 S ribosomes and lack cell organelles like Golgi apparatus, mitochondria, chloroplasts and peroxi­somes.

·       The kingdom Archezoa is now no longer in use. The members of the kingdom Archezoa now belong to the phylum Amoebozoa.

Kingdom Chromista

·  Technological advances in Electron Microscopy allowed the separation of the Chromista from the and Plantae kingdom.

·   Kingdom Chromista consisting of unicellular and multicellular eukaryotic species that share similar features in their Photosynthetic organelles (Plastids). It includes all Protists whose Plastids contain Chlorophyll c, such as some Algae (Brown algae and Cryptomonads), Diatoms, Oomycetes, and Protozoans. Moreover, only Chromists contain Chlorophylla C.

·     The Kingdom Chromista have their Chloroplasts (one of the type of Plastids) within the Lumen of the Rough Endoplasmic Reticulum rather than in the Cytoplasmic matrix (Cytosol) (as is found in the members of Kingdom Plantae).

Cavalier - Smith’s Six Kingdom Model

·       In 1998, Cavalier-Smith had reduced the total number of Kingdoms from Eight to Six:

a)     Kingdom Animalia

b)     Kingdom Protozoa

c)     Kingdom Fungi

d)     Kingdom Plantae (including Red and Green algae)

e)     Kingdom Chromista

f)      Kingdom Bacteria

·    In Cavalier-Smith Model, the Archaebacteria was included as the part of a Sub-kingdom in the Kingdom Bacteria.

Cavalier - Smith’s Seven Kingdom Model

·       Cavalier-Smith and his collaborators revised the classification in 2015, and published it in PLOS ONE.

·      In this scheme they reintroduced the classification with the division of Prokaryotes Superkingdom into two Kingdoms, Kingdom Bacteria (=Eubacteria) and Kingdom Archaea (=Archaebacteria). This is based on the consensus in the Taxonomic Outline of Bacteria and Archaea (TOBA) and the Catalogue of Life. 

·       Cavalier-Smith’s Seven Model Kingdom divides all organisms into 2 Empires and 8 Kingdoms.

ü  2 Empires

c)     Empire Bacteria

§  Kingdom Bacteria

§  Kingdom Archaea

d)     Empire Eukaryota

§  Kingdom Protozoa

§  Kingdom Chromista

§  Kingdom Fungi

§  Kingdom Plantae

§  Kingdom Animalia