Short Answer
Animals are classified into different phyla based on their basic body structure and organization. Important features such as body symmetry, level of organization, presence of body cavity, and type of skeleton are used for this classification.
This system helps scientists group animals with similar fundamental features together. It makes the study of the vast diversity of animals simple, systematic, and easy to understand.
Detailed Explanation :
Basis for Classifying Animals into Different Phyla
The animal kingdom includes a very large number of organisms that differ greatly in shape, size, structure, and way of life. To study this diversity in an organized way, animals are classified into different phyla. A phylum is a major group that includes animals with the same basic body plan and structural features.
The basis for classifying animals into different phyla depends on important and easily observable characteristics. These characteristics reflect the evolutionary development of animals from simple to complex forms. The main bases of classification are explained below in simple language.
Level of Organization
One of the most important bases for classifying animals is the level of organization of their body.
Some animals show cellular level of organization, where cells are loosely arranged and do not form true tissues. Other animals show tissue level, organ level, or organ system level of organization.
Animals with similar levels of organization are grouped into the same phylum. This basis shows how complex the animal body is.
Body Symmetry
Body symmetry refers to the way an animal’s body is arranged.
Animals may be:
- Asymmetrical, with no definite shape
- Radially symmetrical, where body parts are arranged around a central axis
- Bilaterally symmetrical, where the body can be divided into two equal halves
Animals with the same type of symmetry are grouped together. Body symmetry helps in understanding movement and body design.
Number of Germ Layers
During early development, animal embryos form layers of cells called germ layers.
Animals may be:
- Diploblastic, having two germ layers
- Triploblastic, having three germ layers
This feature is used as a basis because it determines the complexity of body structure. Animals with similar germ layers are placed in the same phylum.
Presence or Absence of Body Cavity
Another important basis is the presence or absence of a body cavity, also called coelom.
Animals may be:
- Acoelomate, without a body cavity
- Pseudocoelomate, with a false body cavity
- Coelomate, with a true body cavity
The type of body cavity helps classify animals into different phyla and shows the level of internal organization.
Segmentation of Body
Segmentation refers to the division of the body into repeated units or segments.
Some animals show segmentation, while others do not. Segmented animals have advantages like better movement and specialization of body parts.
This feature is an important basis for separating certain phyla from others.
Type of Skeleton
The type of skeleton present in animals is also used as a basis of classification.
Animals may have:
- No skeleton
- Exoskeleton, a hard outer covering
- Endoskeleton, an internal skeleton
The presence and type of skeleton affect body support, protection, and movement.
Presence of Notochord
The presence or absence of a notochord is a major basis for classifying animals.
Animals with a notochord at any stage of life are placed in one group, while those without it are placed in another. This feature separates highly advanced animals from others.
Mode of Respiration and Circulation
The way animals breathe and circulate blood is also considered.
Some animals use diffusion, some use gills, lungs, or tracheae. Circulation may be absent, open, or closed.
Animals with similar respiratory and circulatory systems are grouped together.
Mode of Reproduction and Development
Reproductive method and development pattern also help in classification.
Animals may reproduce sexually or asexually, and development may be direct or indirect. These features help in understanding relationships among animals.
Evolutionary Relationship
All the above features together help show the evolutionary relationship among animals.
Animals with simple features are considered primitive, while those with complex features are considered advanced. Phyla are arranged to reflect this gradual evolution.
Importance of These Bases
Using these bases helps scientists classify animals correctly and avoid confusion.
It makes the study of animals logical, systematic, and meaningful. It also helps students understand how animals evolved and adapted to different environments.
Conclusion
Animals are classified into different phyla based on fundamental body features such as level of organization, body symmetry, germ layers, body cavity, segmentation, skeleton, and presence of notochord. These bases reflect the structural complexity and evolutionary development of animals. This method of classification helps in organizing the vast diversity of the animal kingdom and makes the study of animal biology simple and systematic.