Anatomy of Earthworm Questions in English

(A) In the earthworm,nephridia are classified based on their location into three types: septal,integumentary,and pharyngeal.
Among these,only the septal nephridia possess a ciliated funnel-like structure called the nephrostome,which helps in collecting coelomic fluid.
Integumentary and pharyngeal nephridia lack a nephrostome.
Therefore,the correct option is $A$.

(B) In earthworm,the first body segment is known as the $Peristomium$ (or buccal segment). The mouth is located ventrally on this segment. The $Prostomium$ is a fleshy lobe that overhangs the mouth and is used as a wedge to force open cracks in the soil.

(A) In the earthworm,the dorsal blood vessel functions as a collecting vessel from the $14th$ segment onwards.
It receives blood from the dorso-intestinal vessels and from the subneural vessels via the commissural vessels.
Therefore,it acts as a collecting channel behind the $13th$ segment.

(C) In Earthworms,the nervous system consists of neurons that are classified based on their functions. These include sensory neurons,which transmit impulses from receptors to the central nervous system; motor neurons,which transmit impulses from the central nervous system to effectors; and adjuster or association neurons,which connect sensory and motor neurons. Therefore,neurons in Earthworms are both sensory and motor.

(D) In $Pheretima$ (earthworm),the body is divided into segments by transverse partitions called septa.
Septa are absent in the first three segments.
Specifically,the first septum is found between the $4^{th}$ and $5^{th}$ segments.
Therefore,septa are absent between the first four segments (i.e.,$1/2, 2/3, 3/4$ and $4/5$ are not present as complete septa,with the first functional septum starting after the $4^{th}$ segment).

(D) In earthworms,nephridia are classified based on their opening into the body.
$1$. Integumentary nephridia open directly to the exterior.
$2$. Enteronephric nephridia open into the alimentary canal (intestine).
These nephridia discharge nitrogenous wastes into the gut,which are then eliminated along with the feces.
This mechanism helps in the conservation of water,thus playing a significant role in osmoregulation.

(A) In $Pheretima$,the dorsal blood vessel is the main collecting vessel.
It possesses valves that prevent the backflow of blood.
These valves are located in front of the septum in each segment,ensuring the unidirectional flow of blood from the posterior to the anterior end.

(B) The correct answer is $B$.
In earthworms,the blood pigment responsible for oxygen transport is haemoglobin.
Unlike vertebrates,where haemoglobin is contained within red blood cells,in earthworms,it is dissolved directly in the blood plasma.

(D) The nephridia of $Pheretima$ (earthworm) are classified based on their location and size.
They are primarily of three types: septal,integumentary,and pharyngeal nephridia.
Based on their structure and size,the nephridia in $Pheretima$ are referred to as Meganephridia because they are large and complex compared to the smaller micrometanephridia found in other annelids.

(D) In $Pheretima$ (earthworm),there are $4$ pairs of hearts,which are known as lateral hearts and lateral-oesophageal hearts.
Specifically,the lateral hearts are located in the $7^{th}$ and $9^{th}$ segments.
These lateral hearts connect the dorsal blood vessel to the ventral blood vessel.
Since there are $2$ pairs of lateral hearts (one pair in the $7^{th}$ segment and one pair in the $9^{th}$ segment),the total number of lateral hearts is $4$.

(D) The correct answer is $D$.
Setae are composed of chitin, which is a tough, nitrogen-containing polysaccharide.
Chitin is highly resistant to chemical degradation, including strong alkalis like $KOH$.
Therefore, setae do not dissolve in $KOH$.
Other statements regarding the speed of movement, oxygen tolerance, and life span are biologically accurate for the earthworm $(Pheretima \, posthuma)$.

(D) The coelomic fluid of the earthworm $(Pheretima)$ is a milky white fluid.
It does not contain haemoglobin,as haemoglobin is present in the blood of the earthworm,not in the coelomic fluid.
The coelomic fluid primarily consists of water,salts,and various types of coelomocytes,which function in immunity and excretion.
Therefore,it is best described as a watery plasma-like fluid.

(C) In earthworm $(Pheretima)$,blood glands are specialized structures located in the $4^{th}$,$5^{th}$,and $6^{th}$ segments.
These glands are situated above the pharyngeal mass.
They are responsible for the production of blood cells and hemoglobin,which remains dissolved in the blood plasma.

(A) The correct answer is $A$.
In the earthworm,each photoreceptor cell contains a nucleus and its cytoplasm possesses a specialized optic organelle known as a phaosome.
This phaosome is an $L$-shaped lens composed of a transparent,hyaline substance that helps in light perception.

(C) The $Chloragogen$ cells are specialized cells found in the coelomic fluid of earthworms,primarily located around the intestine and the dorsal blood vessel.
These cells perform functions analogous to the vertebrate liver,including the storage of glycogen and fats,and the synthesis of urea.
Crucially,$Chloragogen$ cells are responsible for the excretion of metabolic wastes and the removal of silicates that are ingested by the earthworm along with its food from the soil.

(B) The pharyngeal nephridia in $Pheretima$ are located in the $4^{th}, 5^{th},$ and $6^{th}$ segments.
These nephridia open into the anterior part of the alimentary canal,specifically the buccal cavity and the pharynx.
Unlike other types of nephridia,pharyngeal nephridia lack a nephrostome.

(D) Locomotion in the earthworm $(Pheretima)$ is achieved through the coordinated action of the body wall muscles (circular and longitudinal muscles) and the $Setae$.
$1$. The $Setae$ are $S$-shaped structures embedded in the epidermal pits of each segment (except the first,last,and clitellum),which provide grip on the soil.
$2$. The circular muscles cause the body to elongate,while the longitudinal muscles cause the body to shorten.
$3$. By alternating these contractions and using the $Setae$ as anchors,the earthworm moves forward.

(B) In earthworms $(Pheretima)$,nephridia are the excretory organs. Based on their location,they are classified into three types:
$1$. Septal nephridia: Present on both sides of the intersegmental septa of segment $15$ to the last that open into the intestine.
$2$. Integumentary nephridia: Attached to the lining of the body wall of segment $3$ to the last that open on the body surface.
$3$. Pharyngeal nephridia: Present as three paired tufts in the $4th$,$5th$,and $6th$ segments.
Macro nephridia are not a type of nephridia found in earthworms.

(B) In earthworms,spermathecae are specialized sac-like structures located in segments $6-9$.
They are responsible for receiving and storing the sperms received from another earthworm during the process of copulation.
These stored sperms are then utilized later for the fertilization of eggs during cocoon formation.
Therefore,they do not produce sperm; they only store them.

(D) The body of an earthworm,such as $Pheretima$ $posthuma$,is divided into a large number of segments,which are called metameres.
These segments are externally visible as rings.
An adult earthworm typically possesses approximately $100$ to $120$ segments.

(B) The blood of an earthworm $(Pheretima)$ is red in colour.
This red colour is due to the presence of the respiratory pigment haemoglobin.
In earthworms,haemoglobin is not contained within blood corpuscles (like in humans) but is dissolved directly in the blood plasma.
Therefore,the correct description is that the blood is red in colour due to dissolved haemoglobin in the plasma.

(C) In earthworms ($Pheretima$ $posthuma$),four pairs of spermathecae are located in the $6^{th}$ to $9^{th}$ segments.
These are situated on the ventrolateral sides of the intersegmental grooves,specifically one pair in each of the $6^{th}, 7^{th}, 8^{th},$ and $9^{th}$ segments.
They are responsible for storing spermatozoa received during copulation.

(A) In earthworms,septal and pharyngeal nephridia are of the enteronephric type,meaning they discharge their nitrogenous wastes directly into the alimentary canal.
This mechanism allows the organism to reabsorb water from the excretory products before they are eliminated from the body along with the feces.
Therefore,this is a significant evolutionary adaptation for the conservation of water,which is crucial for survival in terrestrial environments.

(D) The dorsal blood vessel of an Earthworm acts as a distributing vessel in the first $13$ segments,where it carries blood to the anterior parts of the body. From the $14^{th}$ segment onwards,it functions as a collecting vessel,receiving blood from the body wall and other organs.

(B) The blood glands in $Pheretima$ (earthworm) are located in the $4^{th}$,$5^{th}$,and $6^{th}$ segments.
These glands are responsible for the production of blood corpuscles and hemoglobin,which are essential for the transport of oxygen.
Among the given options,the production of blood cells (corpuscles) is closely related to the function of phagocytes,which are a type of white blood cell involved in immune defense.
Therefore,the blood glands are involved in the formation of phagocytes.

(A) Earthworms are bisexual (hermaphrodite) animals,meaning they possess both male and female reproductive organs.
However,they exhibit cross-fertilization because the maturation of sperm and eggs occurs at different times,a condition known as protandry.
During mating,two earthworms exchange sperm,which is then stored in the spermathecae to fertilize the eggs later.
Therefore,the correct answer is $A$.

(C) The dental formula of a rabbit is $\frac{2033}{1023}$.
Calculating the total number of teeth: $(\frac{2+0+3+3}{1+0+2+3}) \times 2 = \frac{8}{6} \times 2 = 28$ teeth.
In rabbits,canines are absent,which creates a gap between the incisors and the premolars known as the $Diastema$.
Therefore,option $(c)$ is correct.

(B) Haemoglobin is a respiratory pigment found in many animals.
In earthworms $(Pheretima)$,haemoglobin is not contained within red blood cells but is found dissolved directly in the blood plasma.
In mammals,haemoglobin is a complex conjugated protein (not a dipeptide) localized within the red blood corpuscles $(RBCs)$.
Therefore,the statement that haemoglobin is present in the dissolved state in the blood plasma of earthworms is scientifically correct.

(A) In $Pheretima$ (earthworm), the circulatory system includes specialized pumping organs called hearts.
There are $4$ pairs of lateral hearts.
These are loop-like vessels located in segments $7, 9, 12,$ and $13$.
They connect the dorsal and ventral blood vessels and help in pumping blood.

(D) In $Pheretima$,the dorsal vessel acts as a distributing vessel in the anterior region (first $13$ segments) to supply blood to the body parts.
In the intestinal region (behind the $13^{th}$ segment),it acts as a collecting vessel,receiving blood laden with digested nutrients and ${O_2}$ from the body wall and gut.

(A) In $Pheretima$,lymph glands are located on the $4^{th}$,$5^{th}$,and $6^{th}$ segments.
These glands produce phagocytic cells.
These cells are released into the coelomic fluid,where they perform the function of phagocytosing (engulfing) harmful bacteria and other foreign particles,thereby protecting the earthworm.

(D) In $Pheretima$ (earthworm),nephridia are the primary excretory organs.
Septal nephridia,which are located on both sides of the intersegmental septa behind the $15^{th}$ segment,open into the intestine.
These nephridia are enteronephric,meaning they discharge their nitrogenous waste (primarily urea) directly into the intestinal lumen.
This adaptation helps in the conservation of water by reabsorbing water from the waste before it is excreted,thus playing a crucial role in osmoregulation and the excretion of nitrogenous waste.

(C) In earthworms,nephridia are classified based on their location and the site of waste discharge.
$1$. Integumentary nephridia discharge waste directly to the exterior of the body.
$2$. Septal and pharyngeal nephridia discharge waste into the alimentary canal (digestive tract).
Nephridia that empty into the gut are called enteronephric nephridia.
Therefore,both septal and pharyngeal nephridia are classified as enteronephric.

(B) The correct answer is $(b)$.
Integumentary nephridia are also known as exonephric nephridia.
These are the smallest nephridia,$V$-shaped,and lack a nephrostome.
Integumentary nephridia are scattered throughout the body wall of $Pheretima$ and discharge their waste directly to the exterior of the body.

(D) Nephridia are the excretory organs found in earthworms $(Pheretima)$.
Flame cells (protonephridia) are the specialized excretory structures found in flatworms like $Planaria$.
Both nephridia and flame cells perform the same function of excretion and osmoregulation,although they have different evolutionary origins.
Therefore,nephridia in earthworms are analogous to the flame cells of $Planaria$.

(D) In the reproductive system of a rabbit,the ducts that emerge directly from the testes to transport sperm are known as $Vasa \ efferentia$. These ducts collect spermatozoa from the seminiferous tubules and carry them to the epididymis.

(C) $Pheretima$ (earthworm) is a protostome animal. In protostomes,the blastopore,which is the first opening formed during gastrulation,develops into the mouth. Therefore,the mouth of $Pheretima$ is derived from the blastopore.

(D) In earthworms,locomotion is primarily facilitated by the presence of $Setae$.
$Setae$ are $S$-shaped,chitinous structures embedded in the epidermal pits in the middle of each segment (except the first,last,and clitellum).
These structures act as anchors and provide grip on the soil,allowing the earthworm to move forward through muscular contractions and relaxations of the body wall.

(A) Earthworms have been used by humans for various purposes throughout history. One of the most traditional and common uses of earthworms is as bait for fishing. Anglers use earthworms because their movement and scent are highly attractive to many species of fish.

(A) In an earthworm,the body cavity is filled with coelomic fluid. This fluid is incompressible and acts as a hydrostatic skeleton. It provides structural support to the body,allowing the earthworm to maintain its shape and facilitating movement through the soil by creating pressure against the body wall.

(A) Earthworms ($Pheretima$ $posthuma$) possess a closed circulatory system.
They have four pairs of tubular,contractile hearts located in segments $7, 9, 12,$ and $13$.
These are commonly referred to as lateral hearts because they pump blood from the dorsal vessel to the ventral vessel.
Therefore,earthworms are well-known for the presence of lateral hearts.

(D) In $Pheretima$ (earthworm),the alimentary canal consists of a gizzard.
The gizzard is a thick-walled,muscular organ located in the anterior part of the digestive tract.
Its primary function is to grind the food particles (decaying leaves and organic matter) into smaller pieces,which facilitates further digestion.

(D) In earthworms,nephridia are classified based on their location and the site of waste discharge.
$1$. Septal nephridia are enteronephric,meaning they discharge waste into the alimentary canal.
$2$. Pharyngeal nephridia and Integumentary nephridia are exonephric,meaning they discharge waste directly to the exterior of the body surface.
Therefore,both pharyngeal and integumentary nephridia are responsible for exonephric excretion.

(C) Earthworms are called 'friends of farmers' primarily because they make burrows in the soil,which makes the soil porous. This helps in the respiration and penetration of the developing plant roots. Furthermore,they help in the process of vermicomposting,where they break down organic matter into nutrient-rich humus,thereby significantly increasing the fertility of the soil.

(B) $Chloragogan$ cells are specialized cells found in the earthworm $(Pheretima)$ that are primarily involved in the metabolism of fats,proteins,and carbohydrates,as well as the storage of glycogen and the excretion of nitrogenous wastes. Due to these diverse metabolic and detoxifying functions,they are considered analogous to the liver in humans.

(A) In $Pheretima$ (earthworm),nephridia are classified based on their location into three types: pharyngeal,integumentary,and septal nephridia.
Pharyngeal nephridia are present as three paired tufts in the $4^{th}, 5^{th},$ and $6^{th}$ segments.
These nephridia discharge their waste products into the pharynx and buccal cavity.

(C) In the earthworm ($Pheretima$ $posthuma$),the reproductive system is well-developed.
Specifically,a single female genital pore is present in the mid-ventral line of the $14^{th}$ segment.
This pore is associated with the opening of the female reproductive tract.

(D) In earthworms $(Pheretima)$,nephridia are classified based on their opening into three types: septal,integumentary,and pharyngeal nephridia.
Pharyngeal nephridia are present as three paired tufts in the $4^{th}$,$5^{th}$,and $6^{th}$ segments.
These nephridia discharge their nitrogenous wastes into the alimentary canal.
Specifically,the pharyngeal nephridia of the $4^{th}$ and $5^{th}$ segments open into the buccal cavity,while those of the $6^{th}$ segment open into the intestine.
Therefore,enteronephric nephridia open into both the buccal cavity and the intestine.

(A) In the earthworm ($Pheretima$ $posthuma$),the circulatory system is of the closed type. The dorsal blood vessel is the main collecting vessel. It collects blood from the entire body through various branches and pumps it forward towards the anterior end. Therefore,it acts as the primary vessel for collecting blood from the whole body.

(D) In earthworms,the cocoon is formed by the glandular secretions of the clitellum. As the cocoon moves forward from the clitellum towards the anterior end,it collects ova from the female genital pore and sperms from the spermathecae (which were received during copulation). If the cocoon were to be released from the posterior end,it would fail to pass over the female genital pores and the spermathecal pores. Consequently,neither ova nor sperms would be deposited into the cocoon,leading to a failure in fertilization.