Kingdom animalia shows a great diversity having millions of species.
They are eukaryotic, multicellular heterotrophic organisms.
Basis of Classification
The animals are classified based on arrangements of cells, body symmetry, nature of coelom and pattern of digestive, circulatory or reproductive systems.
(i) Levels of Organisation
All the members of Kingdom Animalia are multicellular but, differ in their organisation of cells.
Cellular level of organisation:
Cells are arranged as loose cell aggregates.
These cells do not form tissues.
All cells are independent in their function.
E.g.: Sponges
Tissue level of organisation:
The cells performing the same function are arranged into tissues.
E.g.: Coelentarata
Organ level of organisation:
Various tissues are organised and grouped together to form organs.
Each organ performs a specific function.
E.g.: Aschelmenthes to chordates.
Organ system level of organisation:
Organs are associated to form functional systems.
Each system is concerned with a specific physiological function.
Organ systems in different groups of animals exhibit various patters of complexities.
Ex: Digestive system, Circulatory system
Digestive System is of two types
Incomplete- It has only one opening that serves as both mouth and anus. E.g.: Platyhelminthes.
Complete- It has two openings, mouth and anus.
Circulatory system is of two types
Open type- In which blood is pumped out of the heart and cells or tissues are directly bathed in blood. E.g.: Arthropods
Closed type- In which blood is circulated through vessels. Ex: All vertebrates
(ii) Body Symmetry
Body symmetry refers to the arrangement of body parts on the sides of the main axis of the body.
Asymmetrical animals:
Any plane passing through the centre of any animal body, does not divide them into equal halves.
E.g.: Sponges
Radially symmetrical animals:
Any plane passing through the centre of any animal body, divides the organism into two identical halves.
Ex: Coelentarata, Ctenophores, Echinodermata
Bilaterally symmetrical animals:
The body can be divided into identical left and right halves in only one plane.
Ex: Annelida, Arthropoda, Vertebrates.
(iii) Body layers
Diplobalstic animals: Animals in which the cells are arranged in embryonic layers. An outer ectoderm and inner endoderm. Ex: Coelentarata
Triploblastic animals: Animals in which the developing embryo has a third germinal layer, mesoderm, in between the ectoderm and endoderm.
Ex: Chordates.
(iv) Coelom
The body cavity between body wall and gut is known as coelom.
Animals having coelom are called coelomates. E.g.: annelid to chordate.
In the animals of phylum aschelminthes, mesoderm is present as scattered pouches, it is called pseudocoelom and the animals are called pseudocoelomates.
Animals in which coelom is absent are called acoelomates. E.g.: Platyhelminthes.
(v) Segmentation
Body of some animals divided into equal external and internal segments with a serial repetition of at least some organs. It is called metamerism.
Ex. Earthworm
(vi) Notochord
Notochord is the mesodermally derived rod like structure formed on the dorsal side during embryonic development.
The animals with notochord are called chordates and those without are called non- chordates.
Classification of Animals
.
They are eukaryotic, multicellular heterotrophic organisms.
Basis of Classification
The animals are classified based on arrangements of cells, body symmetry, nature of coelom and pattern of digestive, circulatory or reproductive systems.
(i) Levels of Organisation
All the members of Kingdom Animalia are multicellular but, differ in their organisation of cells.
Cells are arranged as loose cell aggregates.
These cells do not form tissues.
All cells are independent in their function.
E.g.: Sponges
Tissue level of organisation:
The cells performing the same function are arranged into tissues.
E.g.: Coelentarata
Organ level of organisation:
Various tissues are organised and grouped together to form organs.
Each organ performs a specific function.
E.g.: Aschelmenthes to chordates.
Organ system level of organisation:
Organs are associated to form functional systems.
Each system is concerned with a specific physiological function.
Organ systems in different groups of animals exhibit various patters of complexities.
Ex: Digestive system, Circulatory system
Digestive System is of two types
Incomplete- It has only one opening that serves as both mouth and anus. E.g.: Platyhelminthes.
Complete- It has two openings, mouth and anus.
Circulatory system is of two types
Open type- In which blood is pumped out of the heart and cells or tissues are directly bathed in blood. E.g.: Arthropods
Closed type- In which blood is circulated through vessels. Ex: All vertebrates
(ii) Body Symmetry
Body symmetry refers to the arrangement of body parts on the sides of the main axis of the body.
Any plane passing through the centre of any animal body, does not divide them into equal halves.
E.g.: Sponges
Radially symmetrical animals:
Any plane passing through the centre of any animal body, divides the organism into two identical halves.
Ex: Coelentarata, Ctenophores, Echinodermata
Bilaterally symmetrical animals:
The body can be divided into identical left and right halves in only one plane.
Ex: Annelida, Arthropoda, Vertebrates.
(iii) Body layers
Diplobalstic animals: Animals in which the cells are arranged in embryonic layers. An outer ectoderm and inner endoderm. Ex: Coelentarata
Triploblastic animals: Animals in which the developing embryo has a third germinal layer, mesoderm, in between the ectoderm and endoderm.
Ex: Chordates.
(iv) Coelom
The body cavity between body wall and gut is known as coelom.
Animals having coelom are called coelomates. E.g.: annelid to chordate.
In the animals of phylum aschelminthes, mesoderm is present as scattered pouches, it is called pseudocoelom and the animals are called pseudocoelomates.
Animals in which coelom is absent are called acoelomates. E.g.: Platyhelminthes.
(v) Segmentation
Body of some animals divided into equal external and internal segments with a serial repetition of at least some organs. It is called metamerism.
Ex. Earthworm
Notochord is the mesodermally derived rod like structure formed on the dorsal side during embryonic development.
The animals with notochord are called chordates and those without are called non- chordates.
Classification of Animals
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