CHAPTER 4 - ANIMAL KINGDOM
INTRODUCTION
Millionsof species of animals have been described and it becomes more necessary to classify them to assign a
symmetric position. Animals are sorted out based on some key basic traits such as how their cells are arranged,
the symmetry of their body and whether they have a coelom or not.
Kingdom: Animalia, multicellular and heterotrophic.
BASIS OF CLASSIFICATION
Somefeaturesareused as thebasisof animal classification. Some of them are discussed below.
I. LEVEL OF ORGANIZATION
Though animals are multicellular, the level of organization of cells varies from one animal to another.
1) Cellular Level of Organization: This is the simplest level, where each cell
functions independently, without forming specialized tissues or organs.
Example: Porifera (Sponges)
2) Tissue Level of Organization: Cells aggregate to form tissues, i.e. groups of
similar cells that have a common function and relationship.
Example: Coelenterates, Ctenophora.
3) Organ Level of Organization: Tissues group up to form organs to perform
particular functions. Example: Platyhelminthes.
4) Organ System Level of Organization: A group of organs work together for a
particular function. Example: Aschelminthes to Chordata.
a. Digestive system: There are two forms of digestive system: complete and
incomplete digestive system.
• Incomplete Digestive System: In this form of digestive system, the
digestive system has only one opening, i.e. a single opening serving as
both mouth and anus. Examples: Coelenterates and Platyhelminthes.
• Complete Digestive System: In this form, there are two different
openings: mouth and anus. Examples: Arthropoda, Mollusca, Echinodermata and Aschelminths.
b. Circulatory system: Two types of circulatory system are present: open type and closed type.
OPEN TYPE CLOSED TYPE
(i) Blood is pumped out of the heart. (i) Blood is pumped into a network of tubes
like arteries, veins and capillaries.
(ii) Blood flows with slow speed. (ii) Blood flows with high speed.
(iii) Blood is in direct contact with tissues (iii) Blood is not in direct contact with
and cells of the body. tissues and cells of the body.
(iv) Examples: Arthropods, Molluscs. (iv) Example: Vertebrates.
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,II. BODY SYMMETRY
Animalsshow3typesofbody symmetry:
1) Asymmetry: Inthisform, a body cannot be divided into two equal
halves.
Examples: Porifera.
2) Radial Symmetry: The body can be divided into two identical halves
through any plane passing through the central axis.
Examples: Coelenterates, Ctenophores and Echinoderms.
3) Bilateral Symmetry: The body can be divided into two identical left and right halves
through only one plane.
Examples: Annelids, Arthropods, Molluscs, etc.
III. DIPLOBLASTIC & TRIPLOBLASTIC ORGANIZATION
All animalsdevelop theirtissues,organsand organsystemsfrom the cells that form embryonic layers. Based
on the number of embryonic layers, animals are classified into two groups:
1) Diploblastic animals:
• In diploblastic animals, the cells form two embryonic
layers, i.e. outer layer ectoderm and an inner layer
endoderm.
• Example: Phylum Coelenterata.
• There is an undifferentiated layer called mesoglea
between ectoderm and endoderm.
2) Triploblastic animals:
• The animals in which the developing embryo has a
third germ layer, mesoderm, in between the ectoderm and endoderm are called triploblastic animals.
• Example: Platyhelminthes to Chordates.
IV. COELOM
Thespacebetween the body wall and gut wall lined by mesoderm is called the coelom. There are 3 types of
coelom (body cavity):
1) Coelomates: Animals possessing a coelom or body cavity are known as coelomate animals.
Examples: Annelida, Mollusca, Arthropoda, Echinodermata, Hemichordata and Chordata.
2) Pseudocoelomates: Animals in which the body cavity is not lined by mesoderm; instead, it is present as
scattered pouches between ectoderm and endoderm.
Examples: Aschelminthes.
3) Acoelomates: Coelom or body cavity is absent.
Examples: Platyhelminthes.
V. SEGMENTATION: Some animals have a body that is externally and
internally divided into segments with a serial repetition of organs. This is
called metameric segmentation and the phenomenon is known as metamerism.
Example: Annelida.
VI. NOTOCHORD:
• During embryonic development, some animals develop a
mesodermally derived rod-like structure on their dorsal
side, called a notochord.
• Animals with a notochord are called chordates and those
animals which do not form this structure are called non-
chordates.
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, • Chordate example: Humans and all other members of Phylum Chordata.
• Non-chordate examples: Phylum Porifera to Echinodermata.
• The animal kingdom has been broadly classified into two groups based on the presence or absence of
notochord.
CLASSIFICATION OF ANIMALS
• R.H. Whittaker classified organisms into 5 kingdoms, i.e. Monera, Protista, Fungi, Plantae and Animalia.
• Kingdom Animalia constitutes all animals.
• Among the 5 kingdoms, the largest one is the Animal Kingdom.
• Kingdom Animalia has been classified into 11 different phyla.
The important characteristic features of the different phyla are described.
1) PHYLUM PORIFERA
✓
✓ Members of this phylum are commonly known as “Sponges”.
They are pore bearing animals.
BASIC CHARACTERISTICS/ FEATURES OF PHYLUM PORIFERA:
1. Sponges are aquatic (marine and fresh) and are sessile in nature (attached to the ground)
2. The body is having cellular level of body organization.
3. Digestion is intracellular.
4. They are asymmetrical animals.
5. They are coelomate animals.
6. They are bisexual i.e. sexes are not separate. Eggs and sperms are produced by same individual.
7. Sponges can reproduce both sexually and asexually.
8. Asexual reproduction is by fragmentation and sexual reproduction is by formation of gametes.
9. Fertilization is internal.
10. Development is indirect.
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INTRODUCTION
Millionsof species of animals have been described and it becomes more necessary to classify them to assign a
symmetric position. Animals are sorted out based on some key basic traits such as how their cells are arranged,
the symmetry of their body and whether they have a coelom or not.
Kingdom: Animalia, multicellular and heterotrophic.
BASIS OF CLASSIFICATION
Somefeaturesareused as thebasisof animal classification. Some of them are discussed below.
I. LEVEL OF ORGANIZATION
Though animals are multicellular, the level of organization of cells varies from one animal to another.
1) Cellular Level of Organization: This is the simplest level, where each cell
functions independently, without forming specialized tissues or organs.
Example: Porifera (Sponges)
2) Tissue Level of Organization: Cells aggregate to form tissues, i.e. groups of
similar cells that have a common function and relationship.
Example: Coelenterates, Ctenophora.
3) Organ Level of Organization: Tissues group up to form organs to perform
particular functions. Example: Platyhelminthes.
4) Organ System Level of Organization: A group of organs work together for a
particular function. Example: Aschelminthes to Chordata.
a. Digestive system: There are two forms of digestive system: complete and
incomplete digestive system.
• Incomplete Digestive System: In this form of digestive system, the
digestive system has only one opening, i.e. a single opening serving as
both mouth and anus. Examples: Coelenterates and Platyhelminthes.
• Complete Digestive System: In this form, there are two different
openings: mouth and anus. Examples: Arthropoda, Mollusca, Echinodermata and Aschelminths.
b. Circulatory system: Two types of circulatory system are present: open type and closed type.
OPEN TYPE CLOSED TYPE
(i) Blood is pumped out of the heart. (i) Blood is pumped into a network of tubes
like arteries, veins and capillaries.
(ii) Blood flows with slow speed. (ii) Blood flows with high speed.
(iii) Blood is in direct contact with tissues (iii) Blood is not in direct contact with
and cells of the body. tissues and cells of the body.
(iv) Examples: Arthropods, Molluscs. (iv) Example: Vertebrates.
1
,II. BODY SYMMETRY
Animalsshow3typesofbody symmetry:
1) Asymmetry: Inthisform, a body cannot be divided into two equal
halves.
Examples: Porifera.
2) Radial Symmetry: The body can be divided into two identical halves
through any plane passing through the central axis.
Examples: Coelenterates, Ctenophores and Echinoderms.
3) Bilateral Symmetry: The body can be divided into two identical left and right halves
through only one plane.
Examples: Annelids, Arthropods, Molluscs, etc.
III. DIPLOBLASTIC & TRIPLOBLASTIC ORGANIZATION
All animalsdevelop theirtissues,organsand organsystemsfrom the cells that form embryonic layers. Based
on the number of embryonic layers, animals are classified into two groups:
1) Diploblastic animals:
• In diploblastic animals, the cells form two embryonic
layers, i.e. outer layer ectoderm and an inner layer
endoderm.
• Example: Phylum Coelenterata.
• There is an undifferentiated layer called mesoglea
between ectoderm and endoderm.
2) Triploblastic animals:
• The animals in which the developing embryo has a
third germ layer, mesoderm, in between the ectoderm and endoderm are called triploblastic animals.
• Example: Platyhelminthes to Chordates.
IV. COELOM
Thespacebetween the body wall and gut wall lined by mesoderm is called the coelom. There are 3 types of
coelom (body cavity):
1) Coelomates: Animals possessing a coelom or body cavity are known as coelomate animals.
Examples: Annelida, Mollusca, Arthropoda, Echinodermata, Hemichordata and Chordata.
2) Pseudocoelomates: Animals in which the body cavity is not lined by mesoderm; instead, it is present as
scattered pouches between ectoderm and endoderm.
Examples: Aschelminthes.
3) Acoelomates: Coelom or body cavity is absent.
Examples: Platyhelminthes.
V. SEGMENTATION: Some animals have a body that is externally and
internally divided into segments with a serial repetition of organs. This is
called metameric segmentation and the phenomenon is known as metamerism.
Example: Annelida.
VI. NOTOCHORD:
• During embryonic development, some animals develop a
mesodermally derived rod-like structure on their dorsal
side, called a notochord.
• Animals with a notochord are called chordates and those
animals which do not form this structure are called non-
chordates.
2
, • Chordate example: Humans and all other members of Phylum Chordata.
• Non-chordate examples: Phylum Porifera to Echinodermata.
• The animal kingdom has been broadly classified into two groups based on the presence or absence of
notochord.
CLASSIFICATION OF ANIMALS
• R.H. Whittaker classified organisms into 5 kingdoms, i.e. Monera, Protista, Fungi, Plantae and Animalia.
• Kingdom Animalia constitutes all animals.
• Among the 5 kingdoms, the largest one is the Animal Kingdom.
• Kingdom Animalia has been classified into 11 different phyla.
The important characteristic features of the different phyla are described.
1) PHYLUM PORIFERA
✓
✓ Members of this phylum are commonly known as “Sponges”.
They are pore bearing animals.
BASIC CHARACTERISTICS/ FEATURES OF PHYLUM PORIFERA:
1. Sponges are aquatic (marine and fresh) and are sessile in nature (attached to the ground)
2. The body is having cellular level of body organization.
3. Digestion is intracellular.
4. They are asymmetrical animals.
5. They are coelomate animals.
6. They are bisexual i.e. sexes are not separate. Eggs and sperms are produced by same individual.
7. Sponges can reproduce both sexually and asexually.
8. Asexual reproduction is by fragmentation and sexual reproduction is by formation of gametes.
9. Fertilization is internal.
10. Development is indirect.
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