Test: Earthworm (Old NCERT) - NEET MCQ

Pheretima and its close relatives derive nourishment from decaying organic matter found in the soil. They also feed on the bits of plants and animal matter.

Clitellum or cingulum is a prominent circular band of glandular skin found from the 14^th to 16th segments. It secretes mucus and albumen which helps in the formation of cocoon, and is used from fertilization of the eggs.

A pair of large, thick and muscular vertical vessels, called hearts, are present in each of the segments 7, 9, 12 and 13 in earthworm. Hearts of 7^th and 9^th segments are called lateral hearts that connect dorsal and ventral vessels only. They consist of 4 pairs of valves 

Blood vessels of Pheretima, which have valves are dorsal. Blood passes from backward to forward direction. To prevent the backward flow of the blood, valves are present infront of each septum.

From the 27^th segment upto 23-25 segments in front of the anus in intestine of earthworm, lies a highly glandular and vascular part called typhlosole. It greatly increases the effective absorption area for digested food in the intestine.

Clitellum - secretes cocoon where fertilization and development takes place.
Gizzard - grinds the food
Setae - help in locomotion
Typhlosole - increases area of absorption in intestine

Coelomic fluid of earthworm is alkaline, colourless fluid containing water, slats some proteins and corpuscles. Haemoglobin is not present in coelomic fluid. It is found dissolved in blood plasma giving red colour to blood. Blood is confined to heart and vessels in closed circulatory system.

(i) Septal nephridia and pharyngeal nephridia- Both are exonephric
(ii) Typhlosole- Internal median fold present in the dorsal wall of the intestine of earthworm, meant to increase the absorpton surface area
(iii)Hepatic caeca- Blind tubules present at the junction of foregut and mid-gut in the alimentary canal of the cockroach
(iv) Gizzard- Helps in grinding the soil particles and decaying leaves

Externally the body wall of earthworm is covered by a thin non cellular cuticle below which lies the epidermis two muscle layers (circular and longitudinal) and innermost coelomic  epithelium.

(A) Buccal cavity: 1-3
(B) Pharynx: 3-4
(C) Oesophagus: 5-7
(D) Gizzard: 8-9
(E) Stomach: 9-14
(F) Intestine: 15 to last
(G) Typhlosole: 26-35
So, the correct answer is
'A- (i); B- (ii); C- (iii); D- (iv); E- (v); F- (vi); G- (vii)'.

Alimentary canal of earthworm is a straight structure with variable diameter extending from anus and consisting of buccal cavity, pharynx, oesophage gizzard, stomach and intestine Pharynx is pear-se muscular, extends upto 4th segment, nervering is per on the anterior region in groove between buccal chas and pharynx. Gizzard is oval, most muscular part by internal cuticle. It triturates (grinds) ingested food extends upto segment 8^th. Stomach is a narrow,gland and vascular tube extending from segment 9-14 sphincter is present between gizzard and stomach between stomach and intestine.
Lymph glands occur in each of the segment 26 and to behind it. There are two small, whitish glands one ones side of dorsal blood vessel. They are believed to gerer
phagocytic cells.

Part labelled as 'C' is gizzard which helps in grinding the soil particles in earthworm

Septal nephridia and pharyngeal nephridia earthworm are enteronephric and thus excrete nitrogenous wastes into the lumen of alimentary canal/enteron

Hydraulic skeleton is the system of support founded bodied invertebrates, which relies on the incompresse of fluids contained within the body cavity. In earthworms coelomic fluid is under pressure within the coelom and therefore provides support for internal organs. Due to hydraulic skeleton, during burrowing, the anterior end and aids in relaxation of longitudinal muscles

In Pheretima, the red coloured bodies found in 4^th, 5^th, 6^th segments above the alimentary canal are called blood glands. These glands serve for the manufacture of blood corpuscles (leucocytes) and haemoglobin. They are also believed to be excretory in nature.