Question

Typhlosole in earthworm begins from__________ segment.
A. 15$^{th}$
B. 9$^{th}$
C. 26$^{th}$
D. 27$^{th}$

Answer 1

Hint: As we know that earthworm possess 100-120 segments in its body and its intestines extends from the 15$^{th}$ segment to the last segment and it has a longitudinal fold called Typhlosole that helps in increasing the surface area for absorption.

Complete answer:
We all know that the earthworm (Pheretima posthuma) possesses 100-120 segments in its body and mainly lives in burrows of moist soil. Because of porphyrin pigment it is brown in colour.
The first segment in earthworm’s body is called Peristomium. Setae made up of chitin are present in all segments except the 1$^{st}$ and the last segments.
The digestive system of earthworm is divided into the following segment:
> Mouth is mainly present on the 1$^{st}$ segment.
> On the 1$^{st}$-3$^{rd}$ segments is the Buccal cavity.
> Pharynx is present on 3rd and 4$^{th}$ segments.
> Oesophagus extends from 5$^{th}$ to 7$^{th}$ segments.
> Gizzard is present on 8$^{th}$ and 9$^{th}$ segments.
> Stomach is present from 9$^{th}$ to 14$^{th}$ segments.
> Finally the intestines extend from 15$^{th}$ to the last segment.
> Pharynx helps in secreting mucus, gizzard crushes or grinds the food and passes it to the stomach having calciferous glands whose secretion helps in neutralising the acidic medium present in soil.
> Intestine extends from 15$^{th}$ to the last segment and at the 27$^{th}$ segment, it possesses a longitudinal fold called Typhlosole which helps in increasing the surface area for absorption.
It can be divided into three parts:
(i) Pre-typholosar part starting from 15$^{th}$ to 26$^{th}$ segments,
(ii) Typhlosolar part extending from 26$^{th}$ segment to 95$^{th}$ segment and
(iii) Post- typhlosole part starting from 95$^{th}$ segment to the 120$^{th}$ segment.
The 26$^{th}$ segment also has a pair of tubes called intestinal caeca that produces digestive juices and enzymes.

Hence, the correct answer is (C).

Note: Earthworms have four pairs of heart called lateral hearts which are paired and located in 7$^{th}$ and 9$^{th}$ segment and lateral esophageal hearts which are present in 12$^{th}$ and 13$^{th}$ segments. Pharynx of earthworms has a pharyngeal mass that contains cells called chromophiles which secrete mucus and protease and hence considered analogous with salivary glands.