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A Handbook of Biology

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As over a million (10 Lakh) species of animals have been described till

now, the need for classification becomes all the more important.

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Animals are multicellular and heterotrophic organisms without cell wall

and chlorophyll.

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Kingdom Animalia includes 11 major phyla:

1) Porifera

2) Cnidaria/Coelenterata

3) Ctenophora

4) Platyhelminthes

5) Aschelminthes

6) Annelida

7) Arthropoda

8) Mollusca

9) Echinodermata

10) Hemichordata

11) Chordata

BÅSÏS ØF ÇLÅSSÏFÏÇÅTÏØÑ

1. LËVËLS ØF ØRGÅÑÏSÅTÏØÑ

Based on this, animals are grouped into following levels:

01

Cellular level of organisation: Here, the cells are

arranged as loose cell aggregates. E.g. Porifera.

Tissue level of organisation: Here, the cells

are arranged into tissues. E.g. Cnidarians and

Ctenophores.

02

Organ level of organisation: Here, tissues are

arranged into organs to performs a specific function.

E.g. Platyhelminthes

03

Organ system level of organisation: Here, organs are

associated to form organ system and each system

performs physiological function. E.g. Aschelminthes to

chordates.

04