Classification of Animals

Two Kingdom Classification

Kingdom - Plantae
Kingdom - Animalia

The Two-Kingdom Classification, proposed by Linnaeus in 1758, was based on the following observations:

a) Plants are fixed in the soil, stationary and prepare their own food for growth and nutrition.

b) Animals are capable of movement and they obtain nutrition for their growth and survival from the plants or other animals.

Kingdom Plantae

Also termed, Regnum Vegetabile, it included green plants containing chlorophyll, mosses, ferns, many unicellular organisms, moulds, fungi, lichens, bacteria and multicellular seaweeds.

Kingdom Animalia

Also termed, Regnum Animale, it included unicellular protozoans and multicellular organisms which lacked chlorophyll and were incapable of preparing food by photosynthesis.

Merits of 2-Kingdom Classification:

Initiated systematic methods to classify organisms

Specific characters were studied and distinguished which made the basis of classification.

Demerits of 2-Kingdom Classification:

Some organisms possess characters of both plants and animals. For example, Euglena and Chlamydomonas possess chlorophyll as well as exhibit animal characters.

Bacteria and Cyanobacteria (blue-green algae) are placed in plant kingdom though they are very different. They are without a nuclear envelope and cellular organelles; and also not stationary in soil.

Both photosynthetic and non-photosynthetic organisms are placed together in the kingdom plantae. For example the fungi lack chlorophyll and are saprophytic in nature, they are placed in the plant kingdom.