Parapodia are fundamentally the organs of locomotion used both in creeping and in swimming. Considering they are highly vascularized, they also assist the function of respiration.
Nereis comprises of Parapodia
Nereis is a genus of Polychaeta worms in the family Nereidae. They possess setae and parapodia for locomotion. Every segment of the body, besides the peristomium and the anal segment, bears on either side a flat, fleshy, hollow and vertical flap-like outgrowth called parapodia.
They may have two types of setae and parapodia for locomotion.
- Acicular setae implement support.
- Locomotor setae are for crawling and are the bristles that are evident on the exterior of the Polychaeta.
Two stroke performance
Slow creeping movements of Nereis virens are taken out by the action of parapodia only. During locomotion, each parapodium performs two strokes –
- An effective or backstroke and recovery or forward stroke.
- The combined effective and recovery strokes of numerous parapodia propel the worm forward.
- The parapodia of the two sides work alternatively causing successive waves along each side of the worm.