Question

Septal nephridia of earthworm are-
A. Responsible for excretion
B. Present in all body segments
C. Responsible for keeping the surface moist
D. Present in $4,5,6$ fragments

Answer 1

Hint: Belonging to Opisthopora order, the earthworm is an invertebrate. The body of earthworm is segmented and each contains and protects different types of organs that perform various processes in its body. The circulatory system, muscular system, digestive, nervous, excretory and nervous systems are the types of organic systems that are present in an earthworm.

Complete answer:
-Nephridia are like kidney invertebrates. They are always found in pairs. They help in removing the metabolic wastes from an animal’s body. Septal nephridia are responsible for the excretion in Earthworms.
-These are situated on the inter-segmental septum in between them, $15th$ and $16th$ segments at the posterior side of their body.
-Each of the septa contains about $40$ to $50$ nephridia in front and the same behind too.
-Each segment exhibits $80-100$ septal nephridia, except the $15th$ segment (only $40$ to $50$ nephridia are present there).
-Each septum posse’s nephridia on both the surfaces and they are present in semi circles around its intestine, two of the rows are in front of the septum and two are behind it.
-They are not found in the segments up to $14th$.
-It is considered typical of all the nephridia of Pheretima.
-Each of the septal nephridia consists of the body of nephridium, nephrostome, neck, and terminal duct.
-Nephridia hang freely in the coelom and they are attached only with the help of their terminal ducts.
-They open by the terminal ducts into two septal excretory canals which lie on the posterior surface of the septum; one is present on each side of the intestine, beginning ventrally but dorsally opens in the supra-intestinal excretory duct.
Waste collected by the nephridia is directed outside through the excretory canals and ducts into the intestine's lumen.
-These types of nephridia that open into the intestine are known as Enteronephric nephridia.

Hence, the correct answer is option (A).


Note: The earthworm is made of around $100-150$ segments. About a hundred integumentary nephridia are present throughout the earthworm's body wall (except the first two segments). These tiny nephridia help in channelling the nitrogenous waste from inside of the body of the worm to the outside soil. Several nephridia range from $200-250$ in each segment whereas, in the clitellar region, the number is around $2000-2500$ . With the help of the super intestinal duct, septal nephridia opens into the intestine.