Question

Which of the following is correct about the excretion of earthworm?
(i) Earthworm is mainly ureotelic
(ii)Septal nephridia, present on both sides of intersegmental septa of segment
15 to the last, open into intestine
(iii) Integumentary nephridia, attached to the lining of the body wall of segment 3 to the last, open on the body surface.
(iv) Different types of nephridia are basically similar in structure
(v) Nephridia regulate the volume and composition of body fluids

A)i) and (iv)
B)(iv) and (v)
C)(i), (ii), (iii)
D)All of these

Answer 1

The process of removal from the body of metabolic waste products, including nitrogenous materials such as ammonia, urea, uric acid, amino acid, etc. is called excretion.

Complete answer:
The excretory system consists of nephridia as an excretory organ analogous to the kidney of vertebrates.
Nephridia is a porous, long, thin, coiled tube found in all segments except the first three.
They are of three types, depending on their position in the body:

1)Septal Nephridia/Typic Nephridia
2)Pharyngeal Nephridia
3)Integumentary Nephridia

Septal Nephridia:
They are well developed and the largest nephridia, and found to be attached to both sides of each intersegmental septum behind the 15th segment.
Each septum has 40-50 septic nephridia and is arranged in two rows. So every septum has 80-100 nephridia of the septum.
It consists of 3 parts
1.Nephrostome:
2.Body
3.Terminal duct
Septal nephridia discharges waste products through the canal and ducts into the lumen of the intestine. So they're enteronephric.

Pharyngeal Nephridia;
They are found as paired and lie one pair in each of the 4th, 5th and 6th segments.
They are similar in structure to septal nephridia, but they lack nephrostomy (contain short straight lobe and spirally twisted loop).
Lumen's got a ciliated canal.
The terminal nephric ducts of all the tubules of each segment are joined together to form a single common pharyngeal duct on each side.
They've got three pairs of nephridial canal/duct.
The duct emerges from the 6th segment, which opens into the buccal cavity in the 2nd segment, while the 4th and 5th segment ducts open into the pharynx in the 4th segment.
They discharge waste products directly into the buccal cavity and the pharynx from where they pass through the anus with undigested food. They're called enteronephric nephridia.

Integumentary Nephridia:
They are attached to the inside of the body wall from the 7th to the last segment.
They're smaller than the septal nephridia.
Each nephridium is V-shaped with a short straight lobe and a twisted loop with no nephridiostome or funnel.

There are two ciliated canals in their lumen.
They discharge nitrogenous metabolic waste products directly outside the body through nephridiopores. So they're called exonephric nephridia. Earthworm is ureotelic because its nitrogen waste contains 40 percent urea, 20 percent ammonia, 40 per cent amino acid and other nitrogen compounds.

Hence, the correct answer is option (D)

Note: Since nephridia is richly supplied with capillaries, it collects nitrogenous waste and removes it from the body.Nitrogen waste is thrown out at intervals of three days.