Final Answer:
The features of the Class Oligochaeta include mostly earthworms, repeated body segments, and a closed circulatory system (Option B).
Step-by-step explanation:
Oligochaetes, members of the Class Oligochaeta, are characterized by several distinctive features. Firstly, they are mostly represented by earthworms, which are known for their segmented bodies. Each segment, or metamere, typically contains similar structures and functions, contributing to the efficiency of their locomotion and digestion. The presence of repeated body segments is a key characteristic of this class.
Secondly, Oligochaetes possess a closed circulatory system. Unlike an open circulatory system, which allows hemolymph to circulate freely in body cavities, a closed circulatory system features blood contained within vessels. This enhances the precision and control of nutrient and gas exchange. Earthworms, being part of this class, showcase this closed circulatory system, playing a vital role in their physiological processes.
While Option C mentions leeches, it's important to note that leeches belong to the Class Hirudinea, not Oligochaeta. The latter primarily includes free-living organisms like earthworms that contribute to soil health through their activities. This correction underscores the importance of accurate classification in biology and highlights the need for precise information when studying different taxa within the animal kingdom.