Final answer:
Annelids have bilateral symmetry and are characterized by their segmented body plan, known as metamerism, which includes repeated structures in each segment and supports efficient movement and organ development.
Step-by-step explanation:
Annelids exhibit bilateral symmetry and have a segmented, worm-like body structure. This segmentation, known as metamerism, involves the repetition of internal and external structures in each body segment, facilitating efficient movement and allowing space for organ development. In terms of functionality, annelids possess a well-developed nervous system and a closed circulatory system, where muscular "hearts" in anterior segments pump blood through dorsal and ventral vessels with segmental connections. The presence of a true coelom is central to their complex internal organ structure. Additionally, they feature chaetae, which are bristle-like extensions that serve various roles, including locomotion, particularly in groups such as polychaetes that also have parapodia.