Question

Parapodia are locomotory in function in:-
A. Scolopendra
B. Nereis
C. Centipede
D. Earthworm

Answer 1

Hint: Parapodia are dominantly found in annelids, then in any other phylum. Parapodia are paired, un-jointed lateral growths that have the chaetae. In many groups of sea snails and sea slugs, 'parapodium' is referred to as lateral fleshy protrusions. These parapodia are generally found in annelids.

Complete answer:
 Parapodia are usually the organs of locomotion used both in creeping and in swimming. Since they are extremely vascularised, they also serve the functions of respiration. Nereis is a genus of Polychaete worms within the family Nereidae. They possess setae and parapodia for locomotion. Each segment of the body, except the peristomium and the anal segment, bears on either side a flat, fleshy, hollow and vertical flap-like outgrowth called parapodia. However, the earthworm has parapodia but doesn't use it for locomotion.

Hence, the correct answer is option (B).

Additional information:
Nereis might have two types of setae and parapodia for locomotion. Acicular setae help in providing support. The locomotory setae function is to crawl which are found in the bristles that are visible on the exterior side of the Polychaeta. During the function of locomotion, each parapodium performs two functions - an effective or backstroke and recovery or forward stroke. The combined effective and recovery strokes of numerous parapodia make the worm move forward. The parapodia of the two sides work alternatively, using successive waves along each side of the worm, causing the organism to move or locomote
Most species of polychaete annelids have paired, fleshy parapodia which are segmentally organized along the body axis. Parapodia vary in size and form in each species, and reflect their variety of functions, such as exchange of gases, providing anchorage, providing protection and also for locomotion. Also acts as fans for ventilating a burrow with a flow of freshwater.

Note: Annelids are generally triploblastic, bilaterally symmetrical, metamerically segmented, an acoelomate worm with a thin flexible cuticle around the body. The annelids have three major classes: Polychaeta, Oligochaeta, and Hirudinea.