Short Answer

Symmetry in animal classification refers to the arrangement of body parts of an animal around a central point, axis, or plane. It helps in understanding how an animal’s body is organized and shaped.

Based on symmetry, animals are classified into asymmetrical, radially symmetrical, and bilaterally symmetrical groups. This feature is very important for grouping animals into different phyla.

Detailed Explanation :

Meaning of Symmetry in Animal Classification

Symmetry in animal classification means the balanced arrangement of body parts in an animal. It describes how the left and right sides or different parts of the body are arranged in relation to each other. Symmetry is one of the most important features used to classify animals because it reflects their body plan, movement, and level of evolution.

In biology, symmetry helps scientists understand how animals are built and how their bodies function. Animals with similar types of symmetry are often grouped into the same or related phyla. Symmetry also shows the evolutionary advancement of animals from simple to complex forms.

Asymmetry

Asymmetry means the absence of any definite symmetry. In asymmetrical animals, the body cannot be divided into two equal halves in any plane.

Such animals have an irregular body shape. The parts of the body are not arranged in any fixed pattern. Asymmetry is considered a primitive condition and is found in the simplest animals.

A common example of asymmetrical animals is sponges. Their body structure is very simple, and they lack true tissues and organs. Asymmetry shows a low level of body organization.

Radial Symmetry

Radial symmetry means that the body parts of an animal are arranged around a central axis. In radially symmetrical animals, the body can be divided into similar halves along many planes passing through the central axis.

These animals usually have a cylindrical or circular body shape. Radial symmetry is commonly found in animals that live in water and remain fixed or move slowly.

Examples of radially symmetrical animals include starfish, jellyfish, and sea anemones. This type of symmetry allows animals to receive stimuli from all directions, which is useful for their lifestyle.

Bilateral Symmetry

Bilateral symmetry means that the body of an animal can be divided into two equal and mirror-image halves by only one plane. This plane divides the body into left and right sides.

Bilaterally symmetrical animals have a clear front (head), back, dorsal, and ventral side. This type of symmetry is associated with movement and higher body organization.

Most advanced animals, including worms, insects, birds, and mammals, show bilateral symmetry. This symmetry helps in directed movement and development of complex organs.

Importance of Symmetry in Classification

Symmetry is an important basis for animal classification because it helps group animals with similar body plans.

Animals with asymmetry, radial symmetry, and bilateral symmetry belong to different phyla. For example, sponges are asymmetrical, cnidarians are radially symmetrical, and most higher animals are bilaterally symmetrical.

Symmetry also helps in understanding evolutionary relationships. Bilateral symmetry is considered more advanced than radial symmetry, which in turn is more advanced than asymmetry.

Relation of Symmetry to Level of Organization

There is a close relationship between symmetry and level of body organization.

Asymmetrical animals usually show cellular level of organization. Radially symmetrical animals show tissue level of organization. Bilaterally symmetrical animals usually show organ or organ system level of organization.

Thus, symmetry reflects the complexity and advancement of animals.

Role of Symmetry in Movement and Lifestyle

Symmetry also affects how animals move and interact with their environment.

Radially symmetrical animals can respond equally to stimuli from all directions, while bilaterally symmetrical animals are adapted for active and directional movement.

This makes symmetry a useful feature for understanding animal behavior and adaptation.

Conclusion

Symmetry in animal classification refers to the arrangement of body parts in an animal’s body. It may be asymmetrical, radial, or bilateral. This feature helps scientists classify animals into different phyla, understand their body organization, movement, and evolutionary level. Symmetry is a simple but very important concept that makes the classification and study of animals systematic and easy to understand.