Modern Classification of Animal World

Kingdoms are the highest taxonomic groups of living beings. The major criteria used for delimitation of kingdoms are

(a) Cell structure

(b) Complexity of organisation

(c) Presence or absence of locomotion

(d) Mode of nutrition.

In the beginning, living beings were divided into the two kingdoms of plants and animals. It was followed by three kingdom, four kingdom, and five kingdom classifications.

1. Two Kingdom Classification (Plant kingdom and Animal kingdom)

Biologists since the time of Aristotle divided the living world into two kingdoms : Plants and Animals.

The two kingdom system was given by Linnaeus in 1758 and worked well for a long time.

2. Three Kingdom Classification (Animals, Plantae and Protista)

Ernst Haeckel (1866) a German biologist suggested a third kingdom Protista to include protozoa, algae & fungi. Later on the kingdom Protista was reserved only for unicellular organisms.

3. Four Kingdom Classification

This system was developed by Copeland (1956) with four kingdoms namely Monera, Protista, Plantae and Animalia.

Monera includes prokaryotes (bacteria and blue-green algae).

Fungi continued to remain with plants.

4. Five Kingdom Classification

In 1969 the American ecologist Robert H. Whittaker proposed five kingdom classification comprising Monera, Protista, Plantae, Fungi and Animalia.

It excludes virus from living beings.

Whittaker used three criteria for delimiting the five kingdoms:

(a) Complexity of cell structure

(b) Complexity of body structure

(c) Mode of nutrition.

He also laid stress on bringing out their ecological life styles and phylogenetic relationships.