Basis of Classification of Animals :
The history of the classification is very old. Initially, we classified the plants and animals on their value or utility to man such as useful – harmful, dangerous-non dangerous, edible-inedible. The plant and animal kingdom were differentiated on the basis of cell wall, chlorophyll and nutritional methods.
Taxonomists classified the animals on the basis of certain salient features. The normal five basic features are as follows:-
1. Symmetry :
The animals exhibit from cellular grade of organisation up to tissue grade, organ grade & organ system grade of organisation. These animals exhibit different type of symmetry such as
1. Asymmetrical: When the animal body can’t be divided into two equal parts by any longitudinal cut.
Example- Sponge (Phylum-Porifera)
2. Radial Symmetrical: When the animal body can be divided into two equal parts with the help of any longitudinal cut.
Example- Hydra, sea Anenone (Phylum-Co-elenterata)
3. Bilateral Symmetrical: When the animal body can be divided into two equal parts only by a specific longitudinal cut.
Example- Man, Insect, Butterfly, Frog, Platyhelminthese etc.
2. Germ Layers :
In the embryonic development of the multi cellular animals, the fertilization is followed by cleavage which results in the formation of blastula and gastrula. The gastrula develops two or three germ layers viz- ectodern, mesoderm and endoderm. These germ layers form various body organs. It is one of the basic feature used in animal classification as—
- Diploblastic: The animals winch exhibits two germ layers viz – ectoderm and endoderm
Example- Phylum – coelenterata
- Triploblastic: The animals which develop from three-layered gastrula viz. ectoderm, mesoderm and endoderm.
Example- Phylum – platyhelminthese to phylum Chordata.
3. Coelom :
The coelom is a body cavity which develops during embryonic development of an animal between ectoderm & endoderm, and it may or may not be lined by mesoderm or it may be absent in some animals. The presence absence & type of coelom is also a basic feature used in animal classification –
- Acoelomate: The animals without any cavity between ectoderm and endoderm. There are mesenchyma tissues (mesodermal in origin) between ectoderm & endoderm.
Example- Platyhelminthese.
- Pseudocoelomate: They have a body cavity between ectoderm and endoderm but it is not lined by the mesoderm.
Example- Aschelminthese
- Eucoelomate: They have a body cavity between ectoderm and endoderm which is lined by the mesoderm. It is also c/a true coelom and its is of two types of the basis of origin
(a) Schizocoelomate: The true coelom which is formed by the splitting of the mesoderm during embryonic development. The measoderm along with ectoderm (Body wall) is called as somatic mesoderm and with endodenn (Alimentary canal) is c/a splanchnic mesoderm.
Example- Annelida, Arthropoda, Mollusca.
(b) Enterocoelomate: The true coelom which is formed as a pouch from the endodenn, similarity, the mesoderm layer with ectoderm is c/a somatopleur and with endoderm as splanchnopleur.
Example- Echinodermata. Chordata
4. Segmentation :
The body of many animals consist of few to many segments. They are formed normally during embryonic development and the process is called as segmentation. The segmentation is also a basic feature of animal classification and on this basis animals are divided into 3 groups viz-
Nonsegmented body:- The body of some animals is not divided into segments.
Examples- Porifera. Coelenterata, Aschelminthese etc.
Pseudosegmented body: The body of some animals is pseudosegmented.
Example- Tape worms (Platyhelmmthese)
True Segmented body: The body of some animals exhibit true segmentation which is also called as metameric segmentation.
Example- Annelida, Arthropoda.
