The members of phylum Annelida are known as “the segmented worms”. Their body is metamerically segmented. (Latin annulus = ring). The excretoryunits of these invertebrates are coiled tubules, the nephridia. Example : Nereis, Pheretima and Hirudinaria.
Body Symmetry : Segmented worms have the typical metameric segmentation. The term ‘annelida’ was coined by Lamarck. Their body consists of segments called somites or metameres and ring like grooves known as annuli. They have bilateral symmetry.
Respiration : Respiration in annelids occurs by the skin. In some, gills are present. The skin, respiratory organ is richly supplied with blood vessels. It is permeable. The exchange of gases takes place there. 02 is taken in and C02 is given out.