Anatomy of Earthworm Questions in English

(A, C) The incorrect statements are $(a)$ and $(c)$.
$\Rightarrow$ Correction for $(a)$: Earthworms possess one pair of male genital pores situated on the ventrolateral side of the $18^{th}$ segment.
$\Rightarrow$ Correction for $(c)$: The muscular layer in the body wall of an earthworm consists of an outer layer of circular muscles and an inner layer of longitudinal muscles.
$\Rightarrow$ Statements $(b)$ and $(d)$ are correct. Setae are indeed involved in locomotion,and the typhlosole is a characteristic internal fold of the intestine that increases the surface area for absorption.

(N/A) Although nephridia in earthworms are structurally similar,they are classified into three types based on their location and the segments in which they are found. These types are:
$1$. Septal nephridia: These are present on both sides of the intersegmental septa of segment $15$ to the last,which open into the intestine.
$2$. Integumentary nephridia: These are attached to the lining of the body wall of segment $3$ to the last,which open on the body surface.
$3$. Pharyngeal nephridia: These are present as three paired tufts in the $4th$,$5th$,and $6th$ segments.

(N/A) $\Rightarrow$ The exchange of reproductive cells and the physiological process of reproduction in earthworms can be described as follows:
$(i)$ Earthworms are protandrous,meaning sperm cells mature before egg cells.
$(ii)$ Mating involves the exchange of sperm between two individuals,followed by external fertilization.
$(iii)$ During mating,two earthworms come together in opposite directions,applying their ventral surfaces against each other.
$(iv)$ They exchange sperm packets known as spermatophores.
$(v)$ During this process,the skin surrounding the male genital pore rises to form temporary papillae,which act like a penis to enter the spermathecal pore and keep it open.
$(vi)$ Once one spermatheca is filled,the earthworms shift their positions to align the male genital pore with the other spermatheca. This process typically takes about one hour.
$(vii)$ Sperm cells are stored in the diverticula of the spermathecae,while the ampulla is associated with the secretion of nutrients for the sperm cells.
$(viii)$ Later,both sperm cells and egg cells are deposited into a cocoon,which is secreted by the clitellar glands.
$(ix)$ Fertilization and development occur within the cocoon,which is an external process.

(A) $(i)$ The primary excretory organs in cockroaches are Malpighian tubules. Similarly,the primary excretory organs in earthworms are nephridia.
(ii) The scientific name of the common cockroach is Periplaneta americana. The scientific name of the common earthworm is Pheretima posthuma (or Lumbricus terrestris).

(A) $(i)$ Earthworms possess $4$ pairs of lateral hearts located in segments $7, 9, 12,$ and $13$.
$(ii)$ The excretory organs in earthworms are segmentally arranged coiled tubules called nephridia.

(B) $\Rightarrow$ Earthworms are reddish-brown terrestrial invertebrates.
$\Rightarrow$ They inhabit the upper layer of moist soil.
$\Rightarrow$ During the daytime,they live in burrows made by boring into and swallowing the soil.
$\Rightarrow$ In gardens,their presence can be identified by their faecal deposits,which are known as worm castings.

(B) The circulatory system of an earthworm is classified as a closed type because the blood is always confined within a network of closed blood vessels and capillaries.
Unlike open circulatory systems where blood flows into body cavities (sinuses),in the earthworm,the blood is pumped by the heart through a series of closed vessels,ensuring efficient transport of nutrients and gases throughout the body.

(N/A) $1$. Mating: Earthworms are hermaphrodites,but they perform cross-fertilization. During mating,two earthworms come in contact with each other,facing opposite directions,such that the male genital pores of one worm come in contact with the spermathecal pores of the other.
$2$. Sperm Exchange: Sperms are exchanged between the two worms and are stored in the spermathecae of the partner.
$3$. Cocoon Formation: After mating,the glandular cells of the clitellum secrete a mucous-like substance that forms a girdle or cocoon around the clitellar segments. As the worm moves forward,this cocoon slides over the anterior segments,collecting eggs from the female genital pores and sperms from the spermathecae (which were received during mating).
$4$. Fertilization: Fertilization and development occur within the cocoon,which is then deposited in the soil.

(B) In earthworms ($Pheretima$ $posthuma$):
$1$. $A$ single female genital pore is present in the mid-ventral line of the $14^{\text{th}}$ segment.
$2$. Four pairs of spermathecae are located in the $6^{\text{th}}-9^{\text{th}}$ segments (one pair in each segment).
$3$. The clitellum is a prominent glandular and thickened part of the body wall,covering segments $14, 15,$ and $16$.
$4$. Spermathecae are situated on the ventro-lateral sides of the intersegmental grooves,specifically between segments $5/6, 6/7, 7/8,$ and $8/9$.
Therefore,the statement in option $B$ is correct.

(C) The typhlosole is a large,internal,median fold of the dorsal wall of the intestine in earthworms.
It typically extends from the $26^{th}$ segment to the $22^{nd}-25^{th}$ segment before the anus.
The primary function of the typhlosole is to increase the effective surface area for the absorption of digested food within the intestine.

(A) The earthworm possesses a closed circulatory system.
In this type of circulation,the blood is confined within blood vessels and does not come into direct contact with the body tissues.
Therefore,the correct answer is $A$ (Closed type).

(D) In earthworms,the male genital pore is located in the $18^{th}$ segment,not in the $14^{th}$ segment. The $14^{th}$ segment contains the female genital pore.

(C) In $Pheretima$, the ring vessels (also known as commissural vessels) are characteristic circular vessels found in the stomach region, specifically embedded within its muscular coat.
These vessels are present in the segments from $12^{\text{th}}$ to $13^{\text{th}}$ and onwards up to the last segment.
There are approximately $12$ pairs of these ring vessels per segment in the stomach region.

(C) The typhlosolar region is a specialized part of the intestine in earthworms,extending from the $26^{\text{th}}$ segment to the last $23-25$ segments before the anus.
In this region,the mid-dorsal wall of the intestine forms a longitudinal fold known as the typhlosole.
The primary function of this fold is to significantly increase the effective surface area for the absorption of digested nutrients.

(A) The earthworm,$Pheretima$ $posthuma$,is a monoecious (hermaphrodite) animal.
In earthworms,cross-fertilization occurs because the male reproductive organs mature before the female reproductive organs,a condition known as protandry.
Therefore,the statement that 'ovaries mature first' is incorrect,as testes mature before ovaries.

(C) The clitellum is a prominent,glandular,and vascularized thickening of the skin in the earthworm.
It is located in the $14^{th}$,$15^{th}$,and $16^{th}$ segments of the body.
This region is responsible for secreting mucus and cocoons for reproduction.

(D) In earthworms,in each body segment,except the first,last,and clitellum,there are rows of $S$-shaped setae,embedded in the epidermal pits in the middle of each segment.
Their principal role is in locomotion.

(C) In $Pheretima$,the accessory glands are present in the $17^{th}$ and $19^{th}$ segments.
These glands secrete a sticky fluid that helps in binding the two worms together during the process of copulation.

(B) In earthworms,the dorsal wall of the intestine from the $26^{th}$ segment to the $95^{th}$ segment (except the last $23-25$ segments) forms a median internal fold known as the typhlosole.
This structure is a highly glandular and vascular longitudinal ridge.
Its primary function is to increase the effective surface area for the absorption of digested food.

(A) In $Pheretima$,the blood circulation in the intestine follows a specific pathway.
$1$. The blood flows from the ventral blood vessel into the ventro-intestinal blood vessels $(IV)$.
$2$. From there,it enters the external intestinal plexus $(II)$ located on the outer wall of the intestine.
$3$. It then moves into the internal intestinal plexus $(III)$ within the intestinal wall.
$4$. Finally,the blood is collected by the dorso-intestinal blood vessels $(I)$ and transported to the dorsal blood vessel.
Therefore,the correct sequence of blood flow is $IV \rightarrow II \rightarrow III \rightarrow I$.

(C) Based on the reproductive system of the earthworm (Pheretima):
$A$ represents the Spermathecae,which are located in segments $6-9$.
$B$ represents the Testis sacs,located in segments $10$ and $11$.
$C$ represents the Seminal vesicles,which are large structures in segments $11$ and $12$.
$D$ represents the Ovary,located in segment $13$.
$E$ represents the vas deferens,which runs longitudinally from segment $12$ onwards.
$F$ represents the Accessory glands,located in segments $17$ and $19$.
Therefore,the correct labeling is $A-$ Spermatheca,$B-$ Testis,$C-$ Seminal vesicle,$D-$ Ovary,$E-$ vas deferens,$F-$ Accessory gland.

(A) In $Pheretima$,the $10^{th}$ segment contains the stomach.
When a transverse section is taken through the $10^{th}$ segment,the following structures are observed: stomach,dorsal blood vessel,ventral blood vessel,supraoesophageal vessel,anterior loops,ring vessels,and micronephridia.
These structures are characteristic of the anatomy of the $10^{th}$ segment in earthworms.

(B) In $Taenia$ (a member of $Platyhelminthes$),specialized cells called flame cells are responsible for excretion and osmoregulation.
Similarly,in the earthworm (a member of $Annelida$),coiled,tubular structures called $Nephridia$ perform the function of excretion and osmoregulation.

(B) The notochord is a flexible,rod-like supporting structure that is a characteristic feature of chordates.
Earthworms belong to the phylum $Annelida$,which are non-chordates; therefore,they lack a notochord.
The nerve cord in non-chordates,such as earthworms,is solid,double,and located on the ventral side of the body.
Thus,the notochord is absent,and the nerve cord is ventral.

(C) Earthworms belong to the phylum $Annelida$. They exhibit metameric segmentation,meaning their body is divided both externally and internally into a series of repeated segments. These segments are known as $metameres$ or $somites$.

(D) Earthworms $(Pheretima)$ possess three types of nephridia based on their location:
$1$. Septal nephridia: Present on both sides of the intersegmental septa from the $15^{th}$ segment to the last.
$2$. Integumentary nephridia: Attached to the lining of the body wall of segment $3$ to the last.
$3$. Pharyngeal nephridia: Present as three paired tufts in the $4^{th}, 5^{th},$ and $6^{th}$ segments.
Protonephridia are primitive excretory structures found in organisms like flatworms (Platyhelminthes),not in earthworms.

(C) The sensory system of an earthworm does not have eyes. However,it possesses light-sensitive receptors (photoreceptors) to distinguish light intensities and touch-sensitive receptors (tactile receptors) to feel vibrations in the ground.

(D) Endonephric nephridia are those nephridia that discharge their collected excretory waste into the alimentary canal,from where it is eventually expelled outside through the anus.
Septal nephridia and pharyngeal nephridia are classified as endonephric nephridia.
Exonephric nephridia are those that discharge their excretory waste directly outside the body wall. Integumentary nephridia are exonephric.
Based on the provided figure:
$A$ = Pharyngeal nephridia (Endonephric)
$B$ = Integumentary nephridia (Exonephric)
$C$ = Septal nephridia (Endonephric)
Therefore,both $A$ and $C$ are endonephric nephridia.

(D) In the earthworm $(Pheretima)$,four pairs of spermathecae are located in the $6^{th}, 7^{th}, 8^{th}$ and $9^{th}$ segments.
These structures are responsible for storing the sperms received from another earthworm during the process of copulation.

(D) In earthworms,the female reproductive system consists of a pair of ovaries,which are located laterally in the $13^{th}$ segment.
Additionally,there are $4$ pairs of spermathecae located in the $6^{th}$ to $9^{th}$ segments ($1$ pair per segment).
Since none of the provided options ($A$,$B$,or $C$) correctly describe these anatomical features,the correct answer is $D$.

(A) The prostomium is a small fleshy lobe that overhangs the mouth of an earthworm.
Statement $(a)$ is correct as it acts as a covering for the mouth.
Statement $(b)$ is correct as it is used as a wedge to force open cracks in the soil.
Statement $(c)$ is correct as the prostomium is sensory in function.
Statement $(d)$ is incorrect because the first body segment of the earthworm is the peristomium (or buccal segment),not the prostomium. The prostomium is a pre-oral lobe located anterior to the first segment.
Therefore,statements $(a), (b)$ and $(c)$ are correct.

(N/A) $\rightarrow$ In leeches,a true blood vascular system is absent. Instead,the coelomic space and its fluid have been modified to form the circulatory system. Hence,it is called the haemocoelomic system,and the coelomic fluid is referred to as haemocoelomic fluid.
Blood appears red due to the presence of the respiratory pigment haemoglobin or erythrocruorin,which is found dissolved in the plasma.
Free amoeboid blood corpuscles are present,but there are no red blood corpuscles (erythrocytes).

(A) The earthworm is a reddish-brown terrestrial invertebrate,not an aquatic vertebrate. It belongs to the phylum Annelida. Therefore,statement $A$ is incorrect as it describes the earthworm as an aquatic vertebrate.

(A) The dorsal surface of an earthworm is characterized by the presence of a dark mid-dorsal line,which represents the dorsal blood vessel visible through the skin.
The ventral surface is identified by the presence of genital pores and the absence of the dark mid-dorsal line.
Therefore,the ventral surface is marked by genital pores,and the dorsal surface is marked by the dark mid-dorsal line.

(C) The prostomium is a small,fleshy,lobe-like structure that overhangs the mouth of an earthworm. It serves as a covering for the mouth and acts as a wedge to force open cracks in the soil into which the earthworm may crawl. It is also sensory in function.

(D) In the earthworm ($Pheretima$ $posthuma$),the body is divided into three distinct regions based on the presence of the clitellum:
$1$. Pre-clitellar region: This region consists of segments $1$ to $13$ $(R)$.
$2$. Clitellar region: This is a glandular,non-segmented region covering segments $14$ to $16$ $(P)$.
$3$. Post-clitellar region: This region includes segment $17$ to the last segment of the body $(Q)$.
Therefore,the correct sequence for Pre-clitellar,Post-clitellar,and Clitellar regions is $R, Q, P$.

(D) The structure labeled $P$ in the image of the earthworm $(Pheretima)$ is the clitellum.
The clitellum is a glandular,non-segmented,thickened region of the body wall.
Its primary function is the secretion of mucus and albumin,which are essential for the formation of cocoons during the reproductive process of the earthworm.
Therefore,the correct function is the formation of cocoons.

(B) In earthworms,the excretory organs are segmentally arranged coiled tubules called nephridia.
Each nephridium regulates the volume and composition of the body fluids.
These nephridia open to the exterior through a pore called the nephridiopore,which serves as the exit point for nitrogenous wastes.

(C) In the earthworm (Pheretima),the genital pores are as follows:
$1$. $A$ single female genital pore is present in the mid-ventral line of the $14^{th}$ segment.
$2$. $A$ pair of male genital pores is present on the ventro-lateral sides of the $18^{th}$ segment.
Therefore,there are $1 + 2 = 3$ genital pores in total.

(C) The earthworm $(Pheretima)$ belongs to the phylum Annelida.
Annelids are characterized by metameric segmentation (true segmentation).
They exhibit an organ-system level of body organization.
They possess a closed circulatory system.
However,earthworms are true coelomates (eucoelomates),not pseudocoelomates. Pseudocoelomates are characteristic of the phylum Aschelminthes (roundworms). Therefore,the statement that earthworms are pseudocoelomates is incorrect.

(B) The digestive system of an earthworm consists of a straight tube running from the first to the last segment of the body.
The sequence of the organs is as follows:
$1$. Mouth: Opens into the buccal cavity.
$2$. Pharynx: Follows the buccal cavity.
$3$. Oesophagus: $A$ narrow tube that leads to the gizzard.
$4$. Gizzard: Helps in grinding the soil particles and decaying leaves.
$5$. Stomach: Extends from the $9^{th}$ to the $14^{th}$ segment.
$6$. Intestine: Starts from the $15^{th}$ segment onwards.
Therefore,the correct sequence is: Mouth $\rightarrow$ Pharynx $\rightarrow$ Oesophagus $\rightarrow$ Gizzard $\rightarrow$ Stomach $\rightarrow$ Intestine.

(C) In earthworms,the calciferous glands are located in the stomach region.
These glands secrete calcium carbonate $(CaCO_3)$ into the food.
The primary function of these secretions is to neutralize the humic acid present in the decaying organic matter (humus) that the earthworm consumes.
Therefore,the secretion is alkaline in nature to counteract the acidity of the soil/humus.

(D) In Earthworms,a pair of short and conical structures called intestinal caeca are found in the $26^{th}$ segment,attached to the intestine. In Cockroaches,$6-8$ long and tubular structures called hepatic caeca are found at the junction of the foregut and midgut. Therefore,in Earthworms,they are attached to the intestine,and in Cockroaches,they are located between the foregut and midgut. Based on the options provided,the correct description for the location of caeca in these organisms is $D$.

(B) The typhlosole is a longitudinal fold of the inner wall of the intestine in an earthworm $(Pheretima)$.
Its primary function is to increase the effective surface area of the intestine for the absorption of digested food nutrients.
Therefore,the correct option is $B$.

(B) In humans,blood is red due to the presence of hemoglobin inside the red blood cells $(RBCs)$,but the blood plasma itself is straw-colored or yellowish. However,in the context of comparative biology questions regarding the color of blood/fluid,human blood is considered red. In earthworms $(Pheretima)$,hemoglobin is dissolved directly in the blood plasma,which gives the blood a red color. Therefore,both humans and earthworms possess red-colored blood.

(A) In the digestive system of an earthworm $(Pheretima)$:
$1$. $P$ points to the gizzard,which is a muscular organ located in the $8^{th}-9^{th}$ segments,responsible for grinding food particles.
$2$. $Q$ points to the intestinal caeca,which are paired,conical,glandular structures arising from the intestine in the $26^{th}$ segment.
Therefore,$P$ is the gizzard and $Q$ is the intestinal caeca.

(D) In earthworms,the circulatory system is of the closed type. Blood is confined to the heart and blood vessels. Contractions of the heart pump blood into the blood vessels. Smaller blood vessels supply the blood to the gut (alimentary canal),nerve cord,and the body wall to ensure the delivery of nutrients and oxygen to these tissues.

(A) In earthworms ($Pheretima$ $posthuma$),the blood glands are located in the $4^{th}$,$5^{th}$,and $6^{th}$ segments. These glands produce blood cells and hemoglobin,which remain dissolved in the blood plasma.

(A) In earthworms,the skin is thin,moist,and highly vascularized,which allows for the exchange of gases ($O_2$ and $CO_2$) directly through the body surface by diffusion. This process is known as cutaneous respiration. Therefore,the correct answer is the moist body surface.

(B) In the circulatory system of an earthworm $(Pheretima)$:
$1$. The vessel running along the dorsal side of the alimentary canal is the dorsal vessel $(P)$.
$2$. The lateral oesophageal hearts $(Q)$ are present in segments $7$ and $9$,connecting the dorsal and ventral vessels.
$3$. The anterior loops $(R)$ are present in segments $10-13$,connecting the dorsal and ventral vessels.
Therefore,$P=$ Dorsal vessel,$Q=$ Lateral oesophageal hearts,and $R=$ Anterior loops.