Explain nephridia of earthworm

Explanation

In earthworm, the excretory organs occur as segmentally arranged coiled tubules called nephridia. They are of three types : (i) Pharyngeal nephridia : It is located in segment 4, 5 and 6. (ii) Integumentary nephridia : These are attached to lining of the body wall of segment 3 to the last that open on the body surface. (ili) Septal nephridial : It is present on both the sides of intersegmental septa of segment 15 to the last that open into intestine. There are no nephridia present in first two segments. Integumentary nephridia excrete the excretory substances on the wall of body. This type of excretion is called exonerphic excretion. Pharyngeal and septal nephridia throw the excretory substances into buccal cavity. This type of excretion is called enteronephric excertion. These different type of nephridia are basically similar in structure. Nephridia regulate the volume and composition of the body. 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.