The excretory organs occur as segmentally arranged coiled tubules called nephridia (sing.: nephridium). They are of three types:
(i) septal nephridia, present on both the sides of intersegmental septa of segment 15 to the last that open into intestine.
(ii) integumentary nephridia, attached to lining of the body wall of segment 3 to the last that open on the body surface and
(iii) pharyngeal nephridia, present as three paired tufts in the 4th, 5th and 6′ segments (Figure).
These different types of nephridia are basically similar in structure. Nephridia regulate the volume and composition of the body fluids. A nephridium starts out as a funnel that collects excess fluid from coelomic chamber. The funnel connects with a tubular part of the nephridium which delivers the wastes through a pore to the surface in the body wall into the digestive tube.