Anatomy of Earthworm Questions in English

(B) Chloragogen cells are found in the coelomic fluid of annelids (like earthworms) and are primarily involved in excretion and the synthesis of glycogen and fats,functioning similarly to the vertebrate liver.
Flame cells (protonephridia) are the specialized excretory structures found in Platyhelminthes.
Since both chloragogen cells and flame cells are primarily associated with the excretory function in their respective organisms,they are considered analogous in function.

(D) In earthworms ($Pheretima$ $posthuma$),a pair of male genital pores is present on the ventrolateral sides of the $18^{th}$ segment. These pores are responsible for the release of sperms during copulation.

(A) $Monocystis$ is a genus of protozoan parasites that typically infect the seminal vesicles and coelom of earthworms.
These parasites belong to the phylum $Apicomplexa$ and are commonly found in the reproductive organs of the earthworm,where they complete a part of their life cycle.

(B) The typhlosole is a highly glandular,vascular longitudinal ridge present in the intestine of the earthworm.
Its primary function is to increase the internal surface area of the intestine.
This increased surface area facilitates a more efficient absorption of digested food.

(D) In $Pheretima$,the red-coloured follicular bodies found in the $4th$,$5th$,and $6th$ segments,located above the alimentary canal,are known as blood glands.
These glands are responsible for the production of blood corpuscles and haemoglobin,which are essential components of the circulatory system in earthworms.

(A) The body of the earthworm is brown or clay-coloured.
This characteristic colour is due to the presence of a pigment called porphyrin in the dorsal surface of the body wall.
Porphyrin protects the earthworm from the harmful effects of light.

(C) The correct answer is $C$. Prof. Karm Narayan Bahl of Lucknow University published a famous memoir on the Indian earthworm $Pheretima$ $posthuma$ in $1926$. He was a distinguished zoologist and was awarded the Joy Govind Law Memorial Gold Medal in $1942$ for his notable research in Asiatic Zoology.

(D) $Pheretima \text{ } posthuma$ (earthworm) is known as the 'farmer's friend' or 'nature's ploughman'.
It burrows into the soil, which helps in making the soil porous, allowing better aeration and water infiltration.
Additionally, earthworms consume organic matter and excrete nitrogenous waste, which significantly increases the fertility of the soil.

(A) The clitellar region of the earthworm is referred to as the 'forest of nephridia'.
This is because the clitellar region contains a very high density of nephridia,approximately $2000$ nephridiopores per segment.
Due to this dense concentration,it is metaphorically described as a 'forest of nephridia'.

(C) Chloragogen cells are specialized cells found in the coelomic fluid of earthworms. These cells are analogous to the vertebrate liver and play a crucial role in the metabolism of fats,proteins,and carbohydrates,as well as in the storage of glycogen and the detoxification of the body.

(C) In earthworm,two pairs of genital papillae are situated ventrally on the $17^{th}$ and $19^{th}$ segments.
These structures play a crucial role during the process of copulation by helping to hold the two worms together.

(B) The circulatory system of an earthworm is of the closed type. The dorsal blood vessel acts as the main distributing vessel. In the dorsal blood vessel,the blood flows from the posterior to the anterior end of the body,which is a forward direction.

(D) In an earthworm,setae are present in all segments of the body except the first segment (peristomium),the last segment (anal segment),and the clitellar region. This arrangement is known as the perichaetine arrangement. Therefore,all the given options are correct.

(C) In earthworms, the reproductive system is well-developed.
There is a single female genital pore present in the mid-ventral line on the $14^{th}$ segment.
This pore is responsible for the release of eggs during the reproductive process.

(D) Locomotion in earthworms $(Pheretima)$ is achieved through the coordinated action of the body wall muscles and the $S$-shaped structures called $Setae$.
$1$. The body wall contains both circular and longitudinal muscles.
$2$. Contraction and relaxation of these muscles result in the lengthening and shortening of the body segments.
$3$. $Setae$ are embedded in the epidermal pits of each segment (except the first,last,and clitellum) and act as anchors to provide grip against the substrate.
$4$. Therefore,the combination of muscular contraction and the gripping action of $Setae$ facilitates movement.

(A) In $Pheretima$ (earthworm),there are four pairs of hearts that pump blood.
These are located in segments $7, 9, 12,$ and $13$.
The hearts in segments $7$ and $9$ are known as lateral hearts,while the hearts in segments $12$ and $13$ are known as lateral oesophageal hearts.

(D) In earthworm,fertilization is external and occurs within the cocoon. The cocoon is secreted by the gland cells of the clitellum. As the worm moves backward,it deposits eggs and sperms into the cocoon,where fertilization and development take place.

(A) The correct answer is $A$. During the breeding season,the glandular cells of the clitellum become highly active and secrete a slimy substance that forms a girdle-like covering around the clitellum. Upon exposure to air,this secretion gradually dries and hardens to form a tough but elastic,ring-like egg capsule known as a cocoon.

(B) $Pheretima$ (earthworm) is a hermaphrodite (monoecious) organism,meaning both male and female reproductive organs are present in the same individual.
However,they exhibit cross-fertilization due to a condition called protandry,where the testes mature earlier than the ovaries.

(D) The locomotion in earthworms is a coordinated process involving multiple components:
$1$. The contraction and relaxation of circular and longitudinal muscles create waves of movement.
$2$. The $Setae$ (bristles) act as anchors to provide grip on the substrate.
$3$. The coelomic fluid acts as a hydrostatic skeleton,providing rigidity to the body segments during movement.
Therefore,the correct answer is $D$.

(A) The presence of earthworms in the soil is indicated by the presence of worm castings,which are heaps of small,rounded,soil-like pellets found on the surface. These pellets are the undigested organic matter and soil excreted by the earthworm.

(B) In $Pheretima$ $posthuma$,the clitellum is a prominent,dark-banded,glandular region of the body wall.
It is situated around the $14^{th}$,$15^{th}$,and $16^{th}$ segments.
This region is responsible for secreting mucus and cocoons for reproduction.
Therefore,the correct description is that it is glandular and covers segments $14-16$.

(B) Copulation in earthworms typically occurs at night during the rainy season. This timing is preferred because the moist environment prevents the earthworms from drying out,and the darkness provides protection from predators.

(B) In $Pheretima$ (earthworm),the blood is red in colour. The respiratory pigment,haemoglobin,is dissolved directly in the blood plasma,not contained within blood cells or corpuscles.

(C) Earthworms ($Pheretima$ $posthuma$) do not possess true eyes.
They lack specialized visual organs like eyes.
However,they have light-sensitive receptor cells (photoreceptors) distributed on their dorsal surface,which allow them to detect light intensity and avoid bright light.

(C) Photoreceptors (also known as light-sensitive cells or optic organelles) in earthworms are primarily located on the dorsal surface of the body. These receptors are specialized cells that help the earthworm detect light intensity,which is crucial for its burrowing behavior and avoidance of direct sunlight.

(C) Earthworms are known as the $ \text{'friends of farmers'} $ because they improve soil fertility by burrowing, which aerates the soil, and by producing vermicompost through the decomposition of organic matter. While they may occasionally damage delicate seedlings, their overall contribution to agriculture is overwhelmingly positive. Therefore, they are considered more useful than harmful.

(B) $Pheretima$ $posthuma$ (earthworm) is known as the 'friend of farmers'.
They make the soil porous by burrowing,which helps in the penetration of air and water into the soil.
They also consume organic debris and excrete nitrogen-rich castings,which act as natural fertilizers,thereby increasing soil fertility.

(B) In the earthworm, there are $4$ pairs of large, thick, muscular, and rhythmically contractile hearts.
These hearts are located in segments $7, 9, 12,$ and $13$.

(C) Earthworms are known as the 'friends of farmers'.
They burrow into the soil,which makes the soil porous and loose.
This process,known as vermiculation,helps in the respiration and penetration of developing plant roots.
Additionally,they increase the fertility of the soil by producing vermicompost.

(A) The nephridia in Earthworm are classified based on their location and the site of waste discharge.
$1$. Pharyngeal nephridia and septal nephridia are classified as enteronephric because they discharge their nitrogenous waste products directly into the lumen of the alimentary canal.
$2$. Integumentary nephridia are classified as exonephric because they discharge waste products directly to the exterior of the body.
Therefore,the correct answer is $A$.

(A) In the earthworm ($Pheretima$ $posthuma$),the female reproductive system consists of a pair of ovaries.
These ovaries are attached to the intersegmental septum of the $12^{th}$ and $13^{th}$ segments.
Specifically,the ovaries are located in the $13^{th}$ segment.

(D) In $Pheretima$ (earthworm),the blood is red in color.
This red color is due to the presence of the respiratory pigment haemoglobin.
Unlike vertebrates,where haemoglobin is contained within red blood corpuscles,in $Pheretima$,the haemoglobin is dissolved directly in the blood plasma.
Therefore,the correct description is that the blood is red with haemoglobin in the plasma.

(B) Earthworms are known as the '$ \text{friends of farmers} $'.
They play a crucial role in soil fertility by burrowing, which aerates the soil, and by their excretory products.
Specifically, their nephridial excretions add nitrogenous wastes and other nutrients to the soil, thereby enriching it and improving its quality for crop growth.

(B) Earthworms have been used by humans for various purposes throughout history. One of the oldest documented uses of earthworms is as bait for fishing. Fishermen have traditionally used earthworms to attract and catch fish due to their movement and scent,which are highly effective in aquatic environments.

(B) In earthworms,the blood is red in colour due to the presence of haemoglobin.
Unlike humans,where haemoglobin is contained within the red blood cells (intracellular),in earthworms,the haemoglobin is dissolved directly in the blood plasma.
Therefore,the haemoglobin is intercellular (present between the cells in the plasma).

(B) The common Indian earthworm is $Pheretima$ $posthuma$.
$Pheretima$ is the most widely studied genus of earthworms in India,belonging to the family $Megascolecidae$.

(B) In earthworms,there are two pairs of testes present. These are located in the $10^{th}$ and $11^{th}$ segments,one pair in each segment,on the ventrolateral sides of the alimentary canal.

(B) In earthworm,the blood vascular system is different in the first $13$ segments regarding the number,arrangement,and nature of the blood vessels compared to the rest of the body.

(D) $Chloragogen$ cells are small,star-shaped,yellow cells found in annelids (like earthworms).
They are primarily concerned with the storage of reserve food (glycogen and fat),the deamination of proteins,the formation of urea,and they also play a role in excretion.
Among the given options,fat storage is the most accurate function associated with these cells.

(C) The excretory organs of the earthworm $(Pheretima)$ are segmentally arranged coiled tubules called $Nephridia$.
These structures are responsible for the removal of nitrogenous waste products from the body of the earthworm.
$Flame$ $cells$ are the excretory structures in $Platyhelminthes$,while the $Gizzard$ is a part of the digestive system used for grinding food.

(D) In the digestive system of an earthworm,the stomach is the primary organ responsible for the digestion of food. The food,which consists of decaying organic matter and soil,passes through the mouth,buccal cavity,and pharynx before reaching the gizzard,where it is ground. The stomach then secretes digestive enzymes that break down the organic components of the food.

(A) The life span of an earthworm,such as $Pheretima$ $posthuma$,typically ranges from $1$ to $3$ years in its natural habitat. Factors such as soil moisture,temperature,and predation influence its survival.

(A) Earthworms are hermaphrodites and perform cross-fertilization. During copulation,two earthworms come together and attach their ventral surfaces in opposite directions. This process involves the exchange of sperms between the two individuals. The entire process of copulation in earthworms typically lasts for about $1$ hour.

(A) In $Pheretima$,nephridia are segmentally arranged excretory organs.
They are classified based on their location as septal,integumentary,and pharyngeal nephridia.
Nephridia are absent in the first three segments $(1, 2, 3)$ and the last segment.
While most nephridia are of the micronephridia type,the septal nephridia are often considered meganephridia due to their larger size compared to others.

(B) In the earthworm ($Pheretima$ $posthuma$),the reproductive system includes two pairs of testes and one pair of ovaries.
- The testes are located in the $10^{th}$ and $11^{th}$ segments.
- The ovaries are located in the $13^{th}$ segment.
- Anatomically,the testes are larger and more prominent structures compared to the ovaries,which are relatively smaller,compact,fan-shaped structures.

(C) Nephridia are the excretory organs of earthworms (Phylum $Annelida$).
Flame cells (protonephridia) are the excretory organs of flatworms like Planaria (Phylum $Platyhelminthes$).
Since both structures perform the same function of excretion and osmoregulation despite having different evolutionary origins,they are considered analogous organs.

(A) In $Pheretima$ (earthworm),there are four pairs of spermathecae located in the $6th, 7th, 8th,$ and $9th$ segments.
These spermathecae open to the exterior through spermathecal pores situated on the intersegmental grooves between segments $5/6, 6/7, 7/8,$ and $8/9$.

(D) The $Typhlosole$ is a characteristic internal fold of the dorsal wall of the intestine in $Pheretima$ (earthworm).
It extends from the $26th$ segment to the $25th$ segment before the anus (rectum).
Its primary function is to increase the effective surface area for the absorption of digested food within the intestine.

(A) The pharyngeal glands are located on the roof of the pharynx in the Earthworm. These glands contain chromophil cells. These cells are responsible for the secretion of mucus and proteases,which help in the digestion of food.