Q.What is the function of setae in Pheretima?

[!TLDR] Setae in Pheretima are bristles that anchor the worm against the soil during locomotion. …

[!ANSWER] The setae of Pheretima function as anchoring structures that assist locomotion.

Unlike the numerous, paddle-borne setae of polychaetes, each body segment of Pheretima bears only a few short, simple, chitinous setae projecting directly from the body wall (with no parapodia). During locomotion, the earthworm's alternating waves of circular and longitudinal muscle contraction move the body forward, and at each stage the setae of the segments not currently being pulled forward dig into the surrounding soil, anchoring those segments in place so that the contracting segments elsewhere in the body can generate effective forward thrust rather than simply slipping. In this way, the setae work together with the fluid-filled coelom (acting as a hydrostatic skeleton) and t …

• Confusing Pheretima's simple setae with the parapodia of polychaetes, which are a much larger, paddle-like structure. …