Introduction:
Ascaris is a genus of parasitic nematode worms that infect the intestines of humans and animals. It is important to understand the characteristics of Ascaris for a better understanding of its life cycle and mode of infection.

Explanation:
The correct answer is option 'B', which states that Ascaris is characterized by the presence of neither true coelom nor metamerism. Let's break down the characteristics of Ascaris to understand why option 'B' is the correct answer:

Absence of true coelom:
- Coelom is a fluid-filled body cavity that is completely lined by mesoderm. It is present in most higher animals and plays a crucial role in providing space for organ development and movement.
- Ascaris, however, does not possess a true coelom. Instead, it has a pseudocoelom, which is a partially lined body cavity. The pseudocoelom in Ascaris serves as a hydrostatic skeleton, providing support for the internal organs.

Absence of metamerism:
- Metamerism refers to the presence of repeated body segments in an organism. These segments are similar in structure and function, and they allow for efficient movement and specialization of body regions.
- Ascaris does not exhibit metamerism. Its body is elongated and cylindrical without any visible segmentation. The lack of metamerism in Ascaris is in contrast to other segmented worms such as earthworms.

Other characteristics of Ascaris:
- Ascaris is a dioecious organism, meaning it has separate male and female individuals.
- It has a complete digestive system with a mouth, esophagus, intestine, and anus.
- Ascaris has a protective outer covering called a cuticle, which helps it withstand the harsh conditions of the digestive tract.
- It possesses a well-developed reproductive system and produces large numbers of eggs, which are passed out in the feces of the infected host.

Conclusion:
In conclusion, Ascaris is characterized by the absence of true coelom and metamerism. Understanding these characteristics is important for studying the biology and life cycle of Ascaris, as well as developing effective control measures against this parasitic worm.

The body of Ascaris is elongated, cylindrical gradually tapering at both ends. There is no metameric segmentation. In Ascaris, between the body wall and visceral organs is a spacious fluid-filled cavity. They belong to the phylum Aschelminthes that have pseudocoelom as their body cavity.