Septal nephridia are the typical nephridia and is divisible into four parts as:
a. Nephrostome- Flattened, ciliated with funnel-like proximal end and opens into the coelom by an elliptical aperture.
b. Neck- Ciliated funnel leads into a short, narrow and ciliated tubule as neck.
c. Body- Neck is connected to the main body of the nephridium which is divisible into a small straight lobe and a twice larger twisted lobe. The straight lobe continues as distal limb of twisted loop while the proximal limb is formed by the fusion of neck and the terminal duct.
d. Terminal duct- It is the proximal limb of the twisted loop and is formed at the base of nephridium by the fusion of neck and terminal duct.
Therefore, the correct answer is option C.