Chapter 2 : ANIMAL LIKE PROTISTS

ANIMAL LIKE PROTISTS

THE PROTOZOA

EVOLUTIONARY PERSPECTIVE:

1. Fossil study of protozoans: The fossil record indicates that all Protists and animal hyla were present during the Cambrian period. Cambrian period is about 550million years ago. But only a few fossil evidences are available. Therefore,  the dentists gather evidence by examining the structure and function of living species.

2. Origin of protists: Ancient Archaea were the first living organisms on this earth. The Archaea gave rise to the kingdom Protista about 1.5 billion years ago. The endosymbiont hypothesis explains the mechanism of this evolution of protista. Most dentists agree that the protists arose from more than one ancestral group.

3.Taxonomy of protozoans: The zoologists recognize between 7 and 45 phyla of Ntotists. These phyla have numerous evolutionary lineages Therefore, the protists are polyphyletic. Groups of organisms having  separate origin are called polyphyletie. Kingdom Protista has two groups:
a) Plant like protists (algae): These are primarily autotrophic.

(b)Animal like protists (Protozoa): These are primarily heterotrophic

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