Question

In earthworm, the characteristic internal median fold of dorsal wall of the intestine, called as ‘typhlosole’ is present in
A. $5$th to $9$th segments
B. $9$th to$10$th segments
C. $26$th to $25$th segments
D. $15$th to last segment
E. $35$th to last segment

Answer 1

Typhlosole is defined as an internal fold of intestine or inner wall of the intestine. It occurs in annelids, echinoderms, lampreys and mollusks. As earthworm comes under the phylum annelids, typhlosole is also present in earthworms. It is a part of the earthworm's digestive system. It increases the surface area so that the earthworm efficiently absorbs soil nutrients.

Complete answer
Option A $5$th to $9$th segments: The lining of the intestine occurring in earthworm is folded to form villi structures. One of the villi is bigger than the others and the larger one is called typhlosole. Typhlosole runs from $26$th to $25$th segments mid-dorsally in the earthworm.
Option A is not correct.
Option B $9$th to$10$th segments: As seen above, this option is not suitable.
Hence, Option B is not correct.
Option C $26$th to $25$th segments: This is the correct option as seen in option A explanation.
So, Option C is correct.
Option D $15$th to last segment: It is not probable.
Option D is not correct.
Option E $35$th to last segment: It is not possible.
Option E is not correct.

Therefore, Option C is the correct answer

Note:
Typhlosole is responsible for increasing the effective area of the intestine in earthworms. It is a flap forming a tube within a tube. It is also present in snails. In addition, it enhances the rate of nutrient ingestion. It is also involved in effective diffusion of nutrients. It has multiple origins in different earthworm families. It runs along most of the length of the earthworm.