They are the largest nephridia and lie attached to both sides of each intersegmental septum behind the 15th segment.
Structure of Septal Nephridia
It consists of the following parts:
Arrangement of Septal Nephridia
Each septum behind the 15th segment bears 4 rows of septal nephridia – 2 on anterior pace and 2 on posterior face.
Each row may contain 20-25 nephridia as there are 80-100 nephridia on each septum.
Nephridia remain suspended freely in the coelom of each segment and are attached only by their terminal ducts.
Their terminal ducts open into a pair of septal excretory canals that run parallel to the commissural vessel of their own side.
These canals discharge their contents dorsally into a pair of supra intestinal excretory ducts situated just above the intestine and beneath the dorsal blood vessel extending from 15th to last segment.
These ducts open into the intestine in each segment through narrow ductules each having a sphincter opening. They are enteronephric nephridia.