Question

Which of the following is exonephric nephridia?
(a) Pharyngeal Nephridia
(b) Septal Nephridia
(c) Integumentary nephridia
(d) Integumentary nephridia and pharyngeal nephridia

Answer 1

Hint: Nephridia are the primary organs of earthworm that carry out the duties of excretion and osmoregulation. Based on where they remove the metabolic wastes, they are of two types. Exonephric nephridia discharge the wastes directly outside the body.

Complete answer:
Based on where the nephridia remove the metabolic wastes, they are of two types – enteronephric nephridia and enteronephric nephridia. Exonephric nephridia or ectonephric nephridia are the types of nephridia that directly remove the nitrogenous wastes outside the body of earthworm by nephridiopores( external opening of nephridia) . Enteronephric nephridia eject their wastes into the alimentary canal. In earthworm, only integumentary nephridia are exonephric while septal nephridia and pharyngeal nephridia are enteronephric.
Based on location, 3 types of nephridia can be found in an earthworm -Septal nephridia, Pharyngeal nephridia, and integumentary nephridia.

Properties	Septal Nephridia	Pharyngeal Nephridia	Integumentary Nephridia
Segments	Occur from segment 15 onwards.	Occur in segments 4,5and 6.	Occur in all segments except the first two segments.
Location	Attached to the septa.	Lie on the sides of the gut.	Attached to the inner lining of the body wall.
Number	Vary from 80-100 per segment.	Lie in three paired groups	Vary from 200 to 250 per segment.
Opening of nephridia	In the intestine	Ducts of the 6th segment open into the buccal cavity while those of 4th and 5th open into the pharynx.	Directly to the outside.
Type	Enteronephric	Enteronephric	Ecto Nephric
Waste removal	Remove metabolic wastes from the blood and coelomic fluid	Remove metabolic wastes from the blood only.	Remove metabolic wastes from the blood only.

So, the correct answer is ‘Integumentary nephron’.

Note: Enteronephric nephridia in earthworm assists in keeping the skin moist for cutaneous respiration. Enteronephric nephridia play an important role in the conservation of water by absorbing it via the inner lining of the alimentary canal. 14^th, 15^th,16^th segments (clitellar region) in an earthworm are known as ‘forest of nephridia’ because here, the number of integumentary nephridia increases up to 10 times than the other segments.