Segmented worms make up the Phylum Annelida. The phylum includes earthworms and their relatives, leeches, and a large number of mostly marine worms known as polychaetes. Various species of polychaete are known as lugworms, clam worms, bristleworms, fire worms, sea mice.

Annelida: NCERT Solutions - Diversity In Living Organisms

Introduction:
Annelida is a phylum of segmented worms that includes various species such as earthworms, leeches, and marine worms. These organisms exhibit a high level of diversity in terms of their habitat, morphology, and physiological adaptations. In the NCERT Solutions - Diversity In Living Organisms, the study of Annelida is important as it helps students understand the concept of animal classification and the diversity of life forms on Earth.

Characteristics of Annelida:
Annelids share several common characteristics that distinguish them from other organisms. These characteristics are discussed below:

1. Segmentation: Annelids have a segmented body, with each segment called a metamere. This segmentation allows for greater flexibility and movement.

2. Body Cavity: Annelids possess a true coelom, which is a fluid-filled body cavity that provides space for the development and movement of internal organs.

3. Body Wall: The body wall of annelids consists of an outer cuticle, an epidermis, a circular muscle layer, and a longitudinal muscle layer. These layers enable movement and protection.

4. Excretory System: Annelids have a well-developed excretory system called nephridia. Nephridia help in the removal of waste products from the body.

5. Circulatory System: Annelids possess a closed circulatory system, where blood is contained within vessels. This system helps in the transportation of oxygen, nutrients, and waste products.

6. Respiratory System: Most annelids respire through their body surface, while some possess gills or other specialized structures for respiration.

7. Nervous System: Annelids have a well-developed nervous system, consisting of a ventral nerve cord and ganglia. This system allows for coordination and control of various body functions.

Diversity of Annelida:
Annelids exhibit a wide range of diversity in terms of their habitat and adaptations. The major classes of annelids include:

1. Polychaeta: These are marine worms that have well-developed parapodia for locomotion and numerous chaetae (bristles) for protection.

2. Oligochaeta: This class includes earthworms that live in soil and possess few chaetae. They play a vital role in soil fertility.

3. Hirudinea: These are leeches that are mostly found in freshwater habitats. They have a specialized sucker-like structure for feeding and are often used in medical practices.

Conclusion:
The study of Annelida in the NCERT Solutions - Diversity In Living Organisms provides a comprehensive understanding of the diverse characteristics and adaptations exhibited by these segmented worms. Annelids play crucial ecological roles and have significant economic importance. Therefore, it is essential for students to learn about these organisms to appreciate the complexity and diversity of life on Earth.