ANIMAL KINGDOM AND ITS CLASSIFICATION

ANIMAL KINGDOM AND ITS CLASSIFICATION

NEED FOR CLASSIFICATION –

Out of the known 1.7 million organism; 1.2 million are animals and 0.5 million plants. At present, the largest group of organisms is insects with over 0.75 million species. Many species of plant , animal and microorganism are yet to be discovered. Tropical rain forests and under water reefs seem to possess innumerable undiscovered organisms. Each year about 15,000 new species are discovered. According to rough estimate their can be about 5-30 million species . About 50-100 times more species have become extinct. Therefore, a good system of classification is a must for their identification, study and bringing out inter relationship among themselves.

The branch of biology which is concerned with identification, nomenclature and classification of organisms is called TAXONOMY. The term was coined by de Candolle in 1813. (Gr. Taxis = arrangement and nomos = law).

SYSTEMATICS is the scientific study of the diversity of organisms. The term was coined by Carolus Linnaeus (Father of taxonomy) in 1735. He also introduced BINOMIAL NOMENCLATURE which consists of two parts, the first name of the genus ; the second called the specific, identifies the particular species. He wrote Philosophica  Botanica.

Identification – Finding of correct name and place of an organism in a system  of classification is called identification.

ARISTOTLE  studied a number of animals and their developmental stages. He is known as FATHER OF ZOOLOGY. He wrote Historia Plantarum.

CHARACTERISTIC FEATURES OF ANIMALS.-

Animals are evolved from ancestral PROTISTA by a process of division of labour among cells.

1.       They have eukaryotic cells with no cell wall and plastids.

2.       They show cellular or tissue or organ grade in the level of organization.

3.       Generally shows locomotion

4.       They are heterotrophic (consumers), and usually acquire food by ingestion (holozoic) followed by digestion

5.       They are provided with sensory or nervous system except porifers (sponges)

BODY PLAN –

There are three types of body plans is animal kingdom  -

1.       The cell aggregate plan as seen in sponges with no tissues or organs and exhibit loosely arranged cells. (i.e. no division of labour)

2.       The blind sac plan as seen in coelenterates and flat worms with digestive cavity opening out only by mouth .(No anus).

3.       The tube within a tube plan as seen in remaining animals (from annelids to chordates) with alimentary canal opening at either end by mouth and anus.

Body symmetry –

The body of animals can show following types of symmetry-

1.       Asymmetry – Body cannot be divided into two equal halves e.g. amoeba and sponges.

2.       Bilateral symmetry – Body when cut lengthwise shows two equal mirror halves , but this symmetry may not be internal e. g. annelids, arthopods and other animals.

3.       Radial symmetry – Body can be divided into two equal halves by any cut at any diameter through its longitudinal axis. e.g. hydra and starfish