Respiration System

Annelids have two kinds of respiration depending on different classes. If annelids live in sea or water like annelids in class Polychaeta, they have gills to breathe. Some annelids do not have lugs like earthworm (class Oligochaeta), and they use their outer skin to exchange gas. They get oxygen from the soil and release carbon dioxide from their skins. After they get oxygen, they exchange gas in their body through the circulatory system. So their skins need to keep wet to make gas exchange possibly. Respiration of annelids in class Hirudinea like leeches is similar to earthworm. They also breathe through their skins. However, leeches live in water not in soil. If some leeches cannot get enough oxygen in water, they will move to surface.