The animal that has a segmented body is the Annelida. Annelids are a group of invertebrates that includes earthworms, leeches, and various marine worms. They are characterized by their body segmentation, which is divided into repeated units called segments.

Characteristics of Annelids:
1. Segmented Body: Annelids have a segmented body, with each segment containing a distinct set of organs and systems. This segmentation allows for flexibility and efficient movement.

2. External Features: The body of annelids is elongated and cylindrical. They have a well-defined head and tail region. The body is covered by a thin, moist cuticle that protects the underlying tissues.

3. Coelom: Annelids have a true coelom, which is an internal body cavity that contains the organs. The coelom provides space for organ development, movement, and circulation of fluids.

4. Nervous System: Annelids have a well-developed nervous system. They possess a pair of ganglia (nerve clusters) in each segment, connected by a ventral nerve cord. This allows for coordinated movement and response to stimuli.

5. Circulatory System: Annelids have a closed circulatory system. They possess a muscular blood vessel called the dorsal blood vessel that runs along the back of the animal. The blood is pumped by a series of muscular contractions and carries oxygen and nutrients to the tissues.

6. Respiration: Annelids have various methods of respiration. Some use their moist skin for gas exchange, while others have specialized structures called gills. Earthworms, for example, respire through their skin, which needs to remain moist for efficient gas exchange.

7. Reproduction: Annelids can reproduce both sexually and asexually. Most species are hermaphrodites, meaning they have both male and female reproductive organs. They can exchange sperm with another individual during mating.

Importance of Segmentation:
The segmentation in annelids provides several advantages:
1. Improved Movement: The segmented body allows for better coordination and flexibility during locomotion. The segments can move independently, enabling the animal to navigate through narrow spaces and burrow into the ground.

2. Redundancy: Segmentation provides redundancy in case of injury or damage to a segment. If one segment is injured, the others can still function, minimizing the impact on the overall survival of the organism.

3. Specialization: Each segment in annelids has a specific set of organs and systems. This allows for specialization and division of labor within the body. For example, some segments may be specialized for locomotion, while others are involved in digestion or reproduction.

4. Regeneration: Annelids have a remarkable ability to regenerate lost segments. If a segment is damaged or lost, the annelid can regenerate a new one, complete with the necessary organs and systems.

Overall, the segmented body of annelids is a unique adaptation that provides them with increased flexibility, improved movement, and the ability to regenerate. This characteristic sets them apart from other animal groups like Mollusca, Coelenterata, and Porifera, which do not possess segmentation.

Because true metamerism is the one in which the segmentation of body develops by the segmentation of mesoderm. new segments are not added to body after maturation. it means after the embryonic stage all segments become the same age. moreover, the segmental structures are independent and integrated so that individuality of body is preserved.