You discover a marine annelid with paired, leaf-like parapodia rich in capillaries. Predict their main function, with the justification.
- ALocomotion, because setae anchor the substrate
- BSensory reception via mechanoreceptors
- CGas exchange, because the surface area and blood supply are high
- DGamete transfer, because the parapodia lie near the gonopores
Show answer and explanation
Correct answer: (c) Gas exchange, because the surface area and blood supply are high
Explanation
Parapodia are paired, fleshy flaps on the sides of the body segments of marine annelids (polychaetes, such as *Nereis*). They are used mainly for swimming and crawling.
But when they are leaf-like and rich in capillaries, their main role is gas exchange: the thin, flat flaps give a large surface area, and the blood capillaries close to the surface take up oxygen from the water and give out CO₂. In this case they act as gills.