6 Basis of Classification of Animal Kingdom

Table of Contents

In this article we will discuss about Basis of Classification of Animal Kingdom:- 1. Levels of organisation 2. Symmetry 3. Germinal Layers 4. Coelom 5. Segmentation and 6. Notochord

1. Levels of organisation

I) Cellular level

Multicellular
No coordination among cells
Tissues absent
E.g. Porifera

II) Tissue level

Multicellular
Coordination among cells
Cells are arranged into tissues
E.g. Coelenterates and ctenophores

III) Organ level

Multicellular
Coordination between tissues
Tissues are arranged into organs
E.g. Platyhelminthes and other higher phyla

IV) Organ system level

Multicellular
Coordination between organs
Organs are associated to organ system
E.g. Higher animals

2. Symmetry

An object which can be divided into identical halves are called symmetrical. Based on symmetry, animals are 2 types

I) Asymmetrical

Body Cannot be divided into 2 identical halves
E.g. Porifera, snails etc.

II) Symmetrical
Body can be divided into 2 identical halves
Symmetry is 2 types:- Radial Symmetry and Bilateral symmetry

a. Radial Symmetry
Animal body can be divided into two equal halves along any plane passing through the central axis. E.g. Cnidarians, Ctenophores etc.

b. Bilateral Symmetry
Body can be divided into identical left and right halves along only one plane. E.g. Annelids, Arthropods, Chordates etc.

3. Germinal Layers

Layers of tissue formed during embryonic development
All animals have two or three germ layers during embryonic development
Germ layers eventually give rise to all of an animal’s tissues and organs
Based on the number of germ layers, animals are 2 types
1. Diploblastic animals
2. Triploblastic animals

I) Diploblastic Animals

Two layers present in developing embryo
External ectoderm and internal endoderm
E.g. Porifera and Coelentrates

II) Triploblastic Animals

Three layers present in developing embryo
Ectoderm, mesoderm and endoderm
E.g. Platyhelminthes to Chordates

4. Coelom

Coelom is a body cavity filled with fluid
The Coelom is formed during embryo development
Coelom is lined by mesodermal epithelium cells
Presence or absence of coelom is one of the criteria for classifying animals
Coelom provides space for organs to develop
Coelom is body cavity present between the alimentary canal wall and body wall. The true coelom has a mesodermal origin

I) Acoelomate (Coelom absent)
Space between boday wall & Gut wall is filled with matrix. E.g. Porifera to Platyhelminthes

II) Pseudocoelomate (False Coelom)
The body cavity is not lined by mesoderm. Mesoderm is scattered pouches. E.g. Aschelminthes

III) Coelomate (True Coelom)
Coelom is lined by peritoneal layer and filled with coelomic fluid. E.g. Annelida to Chordata

5. Segmentation

It is also called Metamerism
The body is externally and internally divided into repeated segments
E.g. Annelids & Arthropods

6. Notochord

Notochord is main criteria for Basis of Classification of Animal Kingdom.
It is a mesodermally derived supporting rod formed on the dorsal side during embryonic development in some animals
Animals with notochord are called Cordates and those without notochord are called Non-chordates

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