Similarities and Differences of The Animal Kingdom
CHAPTER 4
ANIMAL KINGDOM
Animal Kingdom is characterized by multicellular, eukaryotic organisms. The cells lack cell walls. They ingest and digest food (holozoic), hence they are heterotrophic. Higher forms show elaborate sensory and neuromotor systems. Majority of them are motile. Reproduction is mostly sexual and embryological development is present in them. About 1.2 million species of animals are described till now. The classification helps to assign a systematic position to newly described species.
4.1 BASIS OF CLASSIFICATION
Though different animals differ in their form and structure, there are some fundamental similarities in them such as arrangement of cells, body symmetry, nature of coelom, diploblastic or triploblastic nature of the body wall, segmentation, presence or absence of notochord etc. These features form the basis for the classification of animals. Some of them are described here.
4.1.1 Levels of organization: The patterns of organization of cells vary in animals in spite of their multicellular nature. The patterns of cellular organization seen in animals are:a) Cellular level of organization – In these animals, the cells of the body form loose aggregates
e.g.:- Sponges.
b) Tissue level of organization- In these animals, cells of the animal carrying out the same function are arranged in tissues e.g.:- Coelenterates.
c) Organ system level of organization- In these animals, tissue are grouped together to form organs, each specialized for a particular function e.g.:- members of Platyhelminthes and other higher phyla. 4.1.2. Body symmetry: The arrangement of body parts around a central point or line determines symmetry. Some animals are asymmetrical which cannot be divided into two equal halves along any plane passing through the centre e.g.:- sponges. Some exhibit radial symmetry where the animal can be divided into two equal halves along any plane passing through the central axis e.g.:- Coelenterates,
Ctenophores and
ANIMAL KINGDOM
Animal Kingdom is characterized by multicellular, eukaryotic organisms. The cells lack cell walls. They ingest and digest food (holozoic), hence they are heterotrophic. Higher forms show elaborate sensory and neuromotor systems. Majority of them are motile. Reproduction is mostly sexual and embryological development is present in them. About 1.2 million species of animals are described till now. The classification helps to assign a systematic position to newly described species.
4.1 BASIS OF CLASSIFICATION
Though different animals differ in their form and structure, there are some fundamental similarities in them such as arrangement of cells, body symmetry, nature of coelom, diploblastic or triploblastic nature of the body wall, segmentation, presence or absence of notochord etc. These features form the basis for the classification of animals. Some of them are described here.
4.1.1 Levels of organization: The patterns of organization of cells vary in animals in spite of their multicellular nature. The patterns of cellular organization seen in animals are:a) Cellular level of organization – In these animals, the cells of the body form loose aggregates
e.g.:- Sponges.
b) Tissue level of organization- In these animals, cells of the animal carrying out the same function are arranged in tissues e.g.:- Coelenterates.
c) Organ system level of organization- In these animals, tissue are grouped together to form organs, each specialized for a particular function e.g.:- members of Platyhelminthes and other higher phyla. 4.1.2. Body symmetry: The arrangement of body parts around a central point or line determines symmetry. Some animals are asymmetrical which cannot be divided into two equal halves along any plane passing through the centre e.g.:- sponges. Some exhibit radial symmetry where the animal can be divided into two equal halves along any plane passing through the central axis e.g.:- Coelenterates,
Ctenophores and