Question

What are the organs of locomotion in Annelids?

Answer 1

Hint: Locomotion is a very general term which means the ability of the organism to move from one place to another. Locomotion in annelids is achieved by the part of the body which is segmented and bristle or hair liked structures.

Complete answer:
The annelids are commonly known as the ringed worms or segmented worms. These are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. Locomotion in annelids is achieved by two structures i.e setae and parapodia.
The locomotion in annelids is most studied in earthworms as it is clearly observed in the earthworm because it lacks appendages and parapodia. Movement of earthworms involves extending their body, anchoring it to a surface with the help of setae, and contracting body muscles. When the worm first starts the forward movement, circular muscles at the anterior end contract, extending the head forward. At the same time, the anterior end of the body lifts from the surface to facilitate forward movement. A wavelike contraction originates in the circulatory muscles then passes toward the posterior end. When the wave of contraction comes close to the mid-region of the body, longitudinal muscles contract, thereby shortening the body. A wave of contraction of longitudinal muscles follows, and the cycle is repeated every time until the movement is on. The setae of a segment is extended by the help of certain body muscles to prevent backward movement of the segment during the contraction process of the longitudinal muscles. The setae have to be retracted during the circular contraction period. The earthworm is capable of reversing the direction of its movement, during this time the waves of contraction pass forward.

Note: Most species of the polychaete annelids have a distinct structure for locomotion which is the fleshy parapodia which are segmentally arranged along the body axis. The parapodia varies from organism to organism greatly in size and it’s formed and performs a variety of functions, which are like a gas exchange, anchorage, protection, and locomotion.