Locomotion in Annelida

Before we discuss the details of locomotion in annelids, we have to recapitulate the major subdivisions of the phylum Annelida. Phylum Annelida contains Polychaeta, Oligochaeta and Hirudinea. The Polychaeta, as generally represented by the marine bristle worm Nereis, have parapodia with numerous setae. The Oligochaeta, comprising mainly the earthworms and a few aquatic species, do not possess parapodia and have fewer setae. The Hirudinea, represented by leeches, lack parapodia and setae but suckers are present on either extremities of the body. These are employed in locomotor activity. Thus, the locomotor components in Annelida include

i. Body musculature,

ii. Hydrostatic skeleton, and

iii. Locomotor structures.

So, Locomotion is the result of co-ordinate effort of all these.