MCQ (Practice) - Earthworm - Lower Animal (Level 1) - Class 11 MCQ

Explanation:
To determine the group in which the earthworm belongs, we need to consider its characteristics and compare it with the characteristics of different animal groups.
The characteristics of the earthworm are as follows:
- It has a long, cylindrical body with a segmented structure.
- It lacks any specialized appendages like legs or antennae.
- It has a moist, slimy skin that helps in respiration.
- It exhibits a closed circulatory system.
- It has a well-developed digestive system with a straight alimentary canal.
- It reproduces sexually, with the presence of both male and female reproductive organs.
Based on these characteristics, we can conclude that the earthworm belongs to the group Oligochaeta.
Key Points:
- Earthworm has a long, cylindrical body with segments.
- It lacks specialized appendages.
- It has a moist, slimy skin for respiration.
- Exhibits a closed circulatory system.
- Has a well-developed digestive system with a straight alimentary canal.
- Reproduces sexually.
Therefore, the correct answer is B. Oligochaeta.

Tube within a tube plan exists in Earthworm
The tube within a tube plan refers to the anatomical structure of certain organisms where there is a tube-like structure within another tube-like structure. In the case of the options given, this plan is observed in Earthworms.
Here is a detailed explanation:
Tube within a tube plan in Earthworm:
- Earthworms have a segmented body consisting of numerous repeating units called segments.
- The external body wall of the earthworm is covered by a thin moist cuticle.
- The body wall consists of an outer circular muscle layer and an inner longitudinal muscle layer.
- The innermost layer of the body wall is the coelomic epithelium, which lines the coelom (the body cavity).
- Within the body cavity, there is a long, straight digestive tube that extends from the mouth to the anus.
- This digestive tube is the inner tube within the earthworm's body.
- The digestive tube is divided into several regions, including the pharynx, esophagus, crop, gizzard, and intestine.
- The digestive tube is surrounded by coelomic fluid, which helps in the movement of nutrients and waste materials.
- The tube within a tube plan allows for efficient digestion and absorption of nutrients in earthworms.
Therefore, the correct answer is A: Earthworm.

Body segmentation in different animal phyla:
A: Porifera (sponges)
- Sponges lack true tissue and organ systems.
- They have a simple body structure without any distinct segmentation.
B: Coelenterata (cnidarians)
- Cnidarians, such as jellyfish and corals, have a radial symmetry.
- They do not exhibit true body segmentation.
C: Annelida (segmented worms)
- Annelids, including earthworms and leeches, exhibit true body segmentation.
- Their bodies are divided into a series of repeating segments.
- Each segment contains a set of similar organs and structures.
- This segmentation allows for specialized functions in different segments.
D: Mollusca (mollusks)
- Mollusks, such as snails, clams, and squids, do not have true body segmentation.
- They may have distinct body regions, but these are not true segments.
In conclusion, the correct answer is C: Annelida. Annelids are the phylum of animals that exhibit true body segmentation.

Segment of earthworm bearing mouth is - Peristomium.
Explanation:
The earthworm has a segmented body, and one of these segments is called the peristomium, which bears the mouth. Here is a detailed explanation of the different segments of an earthworm:
1. Prostomium:
- The prostomium is the first segment of the earthworm's body.
- It is not directly involved in bearing the mouth but lies in front of it.
- It is a sensory organ that helps the earthworm in detecting its environment.
2. Peristomium:
- The peristomium is the second segment of the earthworm's body, located immediately behind the prostomium.
- It bears the mouth, which is the opening through which the earthworm takes in food.
- The peristomium is equipped with a muscular upper lip called the prostomium, which helps in the intake of food.
3. Clitellum:
- The clitellum is a thickened glandular segment located near the anterior end of the earthworm's body.
- It is responsible for the production of a cocoon during reproduction.
- The clitellum does not bear the mouth.
4. Deuterostomium:
- Deuterostomium is not a segment of the earthworm's body.
- It is a term used in embryology to describe the developmental process of certain animals, including some invertebrates and vertebrates.
Therefore, the correct answer is B: Peristomium.

Answer:
The total number of body segments in Pheretima is approximately 100-120.
Explanation:
Pheretima, commonly known as the earthworm, is a segmented worm belonging to the phylum Annelida.
- Earthworms have a long, cylindrical body that is divided into numerous segments called metameres or somites.
- Each body segment of an earthworm contains a set of organs and structures that perform specific functions.
- The total number of body segments can vary depending on the species and size of the earthworm.
- On average, Pheretima has around 100-120 body segments.
- These segments are clearly visible externally as ring-like structures along the length of the worm's body.
- Each segment contains both circular and longitudinal muscles that enable the earthworm to move and burrow through the soil.
In conclusion, the total number of body segments in Pheretima is approximately 100-120.

Bodywall of earthworm is without -
The correct answer is A: Appendage.
Here is a detailed explanation:
1. Earthworm Bodywall:
- The bodywall of an earthworm is the outer covering that protects its internal organs.
- It is made up of several layers, including the epidermis, cuticle, and muscles.
2. Appendages:
- Appendages are external structures or organs that are attached to the bodywall.
- Examples of appendages in other animals include legs, wings, and antennae.
- However, earthworms do not possess any external appendages.
3. Epidermis:
- The epidermis is the outermost layer of the earthworm's bodywall.
- It is a thin, protective layer that covers the entire body surface.
- The epidermis secretes mucus, which helps in locomotion and provides protection against drying out.
4. Setae:
- Setae are bristle-like structures found on the body of an earthworm.
- They are located in the epidermis and help the earthworm in locomotion.
- Earthworms use their setae to grip the soil and move forward.
5. Cuticle:
- The cuticle is a layer present beneath the epidermis in the earthworm's bodywall.
- It is a tough, flexible, and waterproof outer covering.
- The cuticle provides protection and prevents the loss of water from the earthworm's body.
Conclusion:
- The bodywall of an earthworm does not have any appendages.
- It consists of layers such as the epidermis, cuticle, and muscles.
- The epidermis produces mucus, while the cuticle acts as a protective barrier.
- Setae are present on the body surface and aid in locomotion.
- Therefore, the correct answer is A: Appendage.

Pheretima posthuma lives within a burrow mainly to get moisture.

• Pheretima posthuma: Pheretima posthuma is a species of earthworm commonly known as the Indian earthworm or nightcrawler. It is found in moist soil and is known for its burrowing behavior.


• Burrow: A burrow is a tunnel or hole dug by an animal for shelter or protection.


• Moisture: Moisture refers to the presence of water or dampness.

Pheretima posthuma lives within a burrow mainly to get moisture due to the following reasons:

• Water requirement: Pheretima posthuma requires moisture to survive as water is essential for various physiological processes in its body.


• Maintaining hydration: Living within a burrow helps the earthworm to maintain its body hydration levels by reducing the risk of dehydration.


• Protection from desiccation: The burrow provides a moist environment that helps to prevent the earthworm's body from drying out and protects it from desiccation.


• Respiration: Earthworms breathe through their skin, which needs to be kept moist for efficient gas exchange. The burrow provides a suitable environment for respiration.


• Nutrient absorption: Moist soil contains dissolved nutrients that can be absorbed by the earthworm's skin. Living within a burrow allows the earthworm to access these nutrients.

In conclusion, Pheretima posthuma lives within a burrow mainly to get moisture, which is crucial for its survival, hydration, protection, respiration, and nutrient absorption.

The epidermis of earthworm is mainly made up of supportive cells.


The epidermis of an earthworm is the outermost layer of its body and is responsible for protecting the internal organs. It is primarily composed of supportive cells, which provide structural support and help maintain the shape of the earthworm's body. These cells are specialized in their function and contribute to the overall functioning of the epidermis.
Some key points to note about the epidermis of earthworm being mainly made up of supportive cells are:
- Earthworms do not have a true cuticle or skin like other animals. Instead, they have a moist and thin epidermis that covers their body.
- The supportive cells in the epidermis help in maintaining the shape and integrity of the earthworm's body. They provide support to the internal organs and protect them from external damage.
- The epidermis also contains other types of cells, such as gland cells, sensory cells, and muscle cells. These cells work together with the supportive cells to perform various functions, including locomotion, respiration, and excretion.
- The epidermis of an earthworm is permeable to water and gases, allowing for efficient respiration and waste elimination.
- The supportive cells in the epidermis also play a role in regeneration. Earthworms have the ability to regenerate lost segments, and the supportive cells help in the process of tissue regrowth.
In conclusion, the epidermis of an earthworm is mainly composed of supportive cells, which provide structural support and help maintain the shape and integrity of the earthworm's body.

The brown skin colour of Pheretima is due to:

• Porphyrin: Pheretima, commonly known as earthworms, have a brown skin color due to the presence of porphyrin pigments. Porphyrins are organic compounds that contain a tetrapyrrole ring structure. These pigments are responsible for the brown coloration in earthworms.

Other possible options:

• Haemoglobin: Haemoglobin is a protein responsible for transporting oxygen in the blood of many animals. While haemoglobin does contribute to the red coloration of blood, it is not the primary pigment responsible for the brown skin color in Pheretima.


• Haemoerythrin: Haemoerythrin is a respiratory pigment found in some marine invertebrates. It is responsible for oxygen transport in these organisms. However, it is not present in earthworms and therefore not responsible for their brown skin color.


• Chromophils: Chromophils are cells or structures that contain pigments and contribute to coloration in organisms. While earthworms do have chromophils, they are not the main reason for their brown skin color.

In conclusion, the brown skin color of Pheretima is primarily due to the presence of porphyrin pigments.

Pheretima exhibits both external and internal segmentation.

Segmentation refers to the division of the body into repeated segments or sections. Pheretima, also known as earthworm, exhibits both external and internal segmentation.

External segmentation:
- The body of Pheretima is externally segmented into a series of ring-like structures called segments.
- Each segment is separated by grooves or constrictions, giving the appearance of a segmented body.
- This external segmentation is easily visible on the body surface of the earthworm.
Internal segmentation:
- Internally, each segment of Pheretima is further divided into compartments or chambers by transverse partitions called septa.
- These septa extend from the body wall towards the central axis of the earthworm.
- The internal segmentation allows for efficient movement and locomotion, as well as organ specialization within each segment.
Conclusion:
Pheretima exhibits both external and internal segmentation, which is an important characteristic of this organism. This segmentation plays a significant role in its locomotion, digestion, and overall body organization.

Earthworm lacks:
- Alimentary canal: Earthworms have a well-developed alimentary canal, which consists of a mouth, pharynx, esophagus, crop, gizzard, intestine, and anus. The alimentary canal is responsible for the digestion and absorption of food.
- Excretory organs: Earthworms have excretory organs called nephridia, which are responsible for removing metabolic wastes from the body. Nephridia help in maintaining the osmotic balance and removing excess water and nitrogenous waste products.
- Distinct head: Earthworms do not have a distinct head with specialized sensory organs. However, they have a prostomium, which is a fleshy lobe covering the mouth and acts as a sensory organ.
- Reproductive system: Earthworms have a well-developed reproductive system with both male and female reproductive organs. They are hermaphroditic, meaning they have both male and female reproductive structures in the same individual.
Based on the given options, the correct answer is C: Earthworm lacks a distinct head.

Function of Porphyrin in Earthworms
Porphyrin is a pigment that imparts color to earthworms. It serves several functions in their bodies, including:
1. Protection against harmful light rays:
- Porphyrin acts as a natural sunscreen, protecting earthworms from harmful ultraviolet (UV) rays.
- UV rays can cause damage to the tissues and DNA of organisms, and porphyrin helps to minimize this damage.
2. Regulation of body temperature:
- Porphyrin helps in the absorption and regulation of heat from the environment.
- It aids in maintaining the optimal body temperature for earthworms, which is essential for their physiological processes.
3. Defense against predators:
- The bright colors produced by porphyrin in earthworms act as warning signals to predators.
- These colors indicate that the earthworms are toxic or unpalatable, deterring potential predators from attacking them.
4. Communication and mating:
- Porphyrin plays a role in communication and mating behaviors of earthworms.
- It helps in attracting potential mates by signaling their reproductive readiness through specific color patterns.
5. Oxygen transport:
- Porphyrin is involved in the transport of oxygen in the circulatory system of earthworms.
- It binds to hemoglobin, a protein responsible for carrying oxygen, and facilitates its transportation throughout the body.
In conclusion, the main function of porphyrin in earthworms is to protect against harmful light rays. However, it also contributes to regulating body temperature, defending against predators, facilitating communication and mating, and aiding in oxygen transport.

Goblet cells on the epidermis of earthworm secrete mucus.
The detailed solution is as follows:
Goblet cells:
- Goblet cells are specialized cells found in the epidermis of earthworms.
- They are named after their shape, which resembles a goblet or a cup with a wide base and a narrow neck.
Function of goblet cells:
- Goblet cells secrete mucus, a slimy substance.
- Mucus acts as a protective layer and lubricant for the earthworm's body.
Importance of mucus secretion:
- Mucus helps prevent the earthworm's body from drying out by retaining moisture.
- It also helps in reducing friction as the earthworm moves through the soil.
- Mucus secretion aids in the process of burrowing and protects the earthworm's delicate skin from mechanical damage.
Therefore, the correct answer is A: Mucus. Goblet cells on the epidermis of earthworms secrete mucus to protect and lubricate their bodies.

Body cavity of earthworm is
The body cavity of an earthworm is called a schizocoel. This means that the body cavity is formed by the splitting of the mesoderm during embryonic development. The schizocoel is filled with fluid and serves several important functions in the earthworm's body.
Functions of the body cavity (schizocoel) in earthworms:
1. Mechanical support: The fluid-filled body cavity provides support to the internal organs, allowing them to maintain their shape and position within the body.
2. Movement: The body cavity acts as a hydrostatic skeleton, providing a medium against which the muscles can work, allowing the earthworm to move and burrow through the soil.
3. Circulation: The fluid in the body cavity helps in the transport of nutrients, oxygen, and waste products throughout the earthworm's body.
4. Respiration: The body cavity allows for the exchange of gases, such as oxygen and carbon dioxide, through the moist body surface of the earthworm.
5. Digestion: The body cavity houses the digestive organs of the earthworm, including the intestine, crop, and gizzard, where food is broken down and absorbed.
In conclusion, the body cavity of an earthworm is called a schizocoel, which serves several important functions in the earthworm's body, including mechanical support, movement, circulation, respiration, and digestion.

Dorsal median line in earthworm is due to the Dorsal blood vessel. Here is a detailed explanation:
Introduction:
The dorsal median line is a prominent feature found on the dorsal side of an earthworm. It is a raised line that runs longitudinally along the midline of the body. This structure is responsible for various physiological functions in the earthworm.
Explanation:
The dorsal median line in an earthworm is primarily due to the presence of the dorsal blood vessel. This vessel is a major component of the earthworm's circulatory system and runs along the midline of the body.
- The dorsal blood vessel functions as the main pumping organ, responsible for circulating the blood throughout the worm's body.
- It is a thick-walled vessel that extends from the anterior to the posterior end of the earthworm.
- The dorsal blood vessel contracts rhythmically, propelling the blood forward and maintaining the circulation.
- The contractions of the dorsal blood vessel can be observed as a pulsating movement along the dorsal median line.
- The presence of the dorsal blood vessel and its rhythmic contractions give rise to the raised dorsal median line on the earthworm's body.
Conclusion:
In conclusion, the dorsal median line in an earthworm is due to the presence of the dorsal blood vessel. This vessel plays a crucial role in the earthworm's circulatory system, pumping blood and maintaining circulation throughout the body.

The earthworm moves with the help of:
- Setae: The earthworm has small bristle-like structures called setae on its body. These setae anchor the worm to the ground and help it move by gripping the soil.
- Muscles: The earthworm has both longitudinal and circular muscles in its body. The longitudinal muscles contract, causing the worm to lengthen and become thinner, while the circular muscles contract, making the worm shorter and thicker. By alternately contracting and relaxing these muscles, the earthworm is able to move forward.
- Coelomic Fluid: The earthworm also uses its coelomic fluid, which fills the body cavity, to help with movement. The fluid acts as a hydraulic skeleton, providing support and allowing the worm to push against the ground.
- Peristalsis: Peristalsis is a wave-like muscle contraction that helps the earthworm move. It involves the contraction and relaxation of the circular muscles along the length of the worm, creating a squeezing motion that propels it forward.
Overall, the earthworm's movement is a coordinated effort between its setae, muscles, coelomic fluid, and peristalsis.

The setae of an earthworm are made up of chitin. Chitin is a tough, flexible, and insoluble polysaccharide that is found in the exoskeletons of arthropods and the cell walls of fungi. It is a type of structural carbohydrate that provides support and protection to various organisms.
Here is a detailed explanation of why the answer is A - chitin:
- Chitin:
- Chitin is a complex carbohydrate that is composed of repeating units of N-acetylglucosamine.
- It is a strong and flexible material that provides structural support and protection.
- It is commonly found in the exoskeletons of arthropods (such as insects, crustaceans, and spiders) and the cell walls of fungi.
- Chitin is also present in the setae of earthworms.

- Earthworm setae:
- Setae are bristle-like structures that protrude from the body of an earthworm.
- They are arranged in rows along the segments of the earthworm's body.
- Setae play a crucial role in locomotion by providing traction and grip as the earthworm moves through the soil.
- The setae are embedded in the epidermis of the earthworm's body wall.
- The setae help the earthworm anchor itself in the soil, preventing it from being pulled out by predators or disturbed by external forces.

- Reasoning:
- Cartilage (option B) is a type of connective tissue found in vertebrates, not in earthworms.
- Pectin (option C) is a type of polysaccharide found in the cell walls of plants, not in earthworms.
- Cuticle (option D) is a waxy, protective layer found on the surface of the epidermis in many organisms, but it is not directly related to the composition of earthworm setae.
- Chitin (option A) is the correct answer as it is the main component of earthworm setae, providing strength and flexibility to these bristle-like structures.
Therefore, the correct answer is A: Chitin.

The middle part of setae of earthworm is called as Nodulus.

• Setigerous sac: The setigerous sac is the glandular structure in an earthworm that produces the setae.


• Setal cell: The setal cell is the individual cell that forms the setae.


• Nodulus: The nodulus is the middle part of the setae, which is thicker and more flexible compared to the other parts.


• Basal part: The basal part refers to the base or attachment point of the setae on the earthworm's body wall.

The setae are bristle-like structures found on the body segments of earthworms. They help the earthworm move through the soil and anchor it during locomotion. The setae are composed of chitin, a tough and flexible material.
The nodulus, being the middle part of the setae, provides flexibility and strength to the setae, allowing them to withstand the forces exerted during movement. The nodulus is thicker than the other parts of the setae, which helps in preventing breakage.
In summary, the middle part of the setae of an earthworm is called the nodulus.

Answer:
The cuticle of an earthworm is secreted by the epidermis. Here is a detailed explanation:
Epidermis:
- The epidermis is the outermost layer of cells in the body of an earthworm.
- It is responsible for the secretion of the cuticle, which is a protective layer that covers the worm's body.
- The cuticle is a thin, flexible, and translucent layer that helps in preventing desiccation (drying out) and provides protection against physical damage.
Other options:
- Hypodermis: The hypodermis is a layer of cells located beneath the epidermis. It does not secrete the cuticle.
- Peritoneum: The peritoneum is the innermost layer of cells that lines the body cavity of the earthworm. It is not involved in the secretion of the cuticle.
- Muscular layer: The muscular layer is responsible for the movement and locomotion of the earthworm. It does not secrete the cuticle.
In conclusion, the cuticle of an earthworm is secreted by the epidermis.

Locomotion of earthworm involves:
- Contraction of the body: Earthworms have longitudinal muscles running along their body segments. When these muscles contract, the segments become shorter and thicker, allowing the earthworm to move forward.
- Anchorage of the body: Earthworms use their setae (bristle-like structures) to anchor themselves in the soil. By extending and retracting the setae, they can grip the soil and prevent themselves from slipping backward while moving forward.
- Extension of the body: Earthworms extend their body by stretching out their segments. This extension occurs after the contraction of the muscles, pushing the body forward.
- All of the above: The correct answer is D, as all of the mentioned processes are involved in the locomotion of earthworms.
In summary, the locomotion of earthworms involves the contraction of the body, anchorage of the body using setae, and extension of the body. These coordinated movements allow earthworms to crawl through the soil and navigate their environment.

The coelomic fluid in earthworm is alkaline.
Explanation:
The coelomic fluid is a type of body fluid found in the coelom, which is the body cavity of earthworms. It serves several important functions in the earthworm's body.
Functions of coelomic fluid:
- Transport of nutrients, respiratory gases, and waste products.
- Regulation of osmotic balance and pH levels.
- Protection against pathogens and foreign substances.
pH of coelomic fluid:
- The pH of the coelomic fluid in earthworms is alkaline, meaning it has a pH value greater than 7.
- This alkaline pH helps in neutralizing the acidic metabolic waste produced by the earthworm's tissues, maintaining the overall pH balance in the body.
Importance of alkaline pH:
- The alkaline pH of the coelomic fluid allows for efficient enzymatic activity within the earthworm's body.
- It also helps in the digestion of organic matter in the earthworm's gut, as the enzymes involved in digestion function optimally in an alkaline environment.
In conclusion, the coelomic fluid in earthworms is alkaline, which is important for various physiological processes and maintaining the overall pH balance in the body.

Answer:
The most numerous and largest cells present in the coelomic fluid of earthworm are phagocytes. Phagocytes are specialized cells that play a crucial role in the immune response of earthworms. They are involved in engulfing and destroying foreign particles, such as bacteria and other pathogens.
Here is a detailed explanation:
1. Coelomic fluid:
- The coelomic fluid is the fluid found in the coelom, which is the body cavity of earthworms.
- It serves various functions such as transport of nutrients, waste removal, and immune defense.
2. Phagocytes:
- Phagocytes are a type of white blood cells that are involved in the immune response of earthworms.
- They are responsible for engulfing and destroying foreign particles, such as bacteria and other pathogens.
- Phagocytes play a crucial role in protecting the earthworm's body from infections and diseases.
3. Other cell types in the coelomic fluid:
- Mucocytes: These cells produce mucus, which helps in lubricating the earthworm's body and protecting it from mechanical damage.
- Chloragogen cells: These cells are involved in the storage and metabolism of nutrients, as well as the detoxification of harmful substances.
- RBCs (Red Blood Cells): Earthworms do not possess true RBCs like vertebrates. Instead, they have colorless blood cells called amebocytes, which are involved in the transport of oxygen and nutrients.
4. Conclusion:
- Among the various cell types present in the coelomic fluid of earthworms, the most numerous and largest cells are phagocytes.
- Phagocytes are specialized white blood cells that play a crucial role in the immune response of earthworms by engulfing and destroying foreign particles.
- Other cell types present in the coelomic fluid include mucocytes, chloragogen cells, and amebocytes (colorless blood cells).

Explanation:
During burrowing, earthworms use their anterior end to push through the soil. This part of the body becomes turgid and acts as a hydraulic skeleton. The turgidity is maintained by the coelomic fluid present in the earthworm's body cavity.
The coelomic fluid is a watery fluid that fills the coelom, which is the body cavity of the earthworm. It provides support and rigidity to the anterior end, allowing it to push against the soil without collapsing. This hydraulic skeleton assists in the movement and burrowing of the earthworm.
The other options mentioned in the question (setae, circular muscles, and longitudinal muscles) are also important for the movement and burrowing of earthworms, but they do not directly contribute to the turgidity and hydraulic skeleton of the anterior end.
In summary, the coelomic fluid present in the earthworm's body cavity is responsible for maintaining turgidity and acting as a hydraulic skeleton during burrowing.

Chloragogen cells, also called as y cells, are cells in annelids that function similarly to the liver in vertebrates. The cells store glycogen and neutralize toxins and are present in coelomic fluid of some annelids. They are yellowish in colour due to the presence of yellow granules called chloragosomes.

The unique characteristic of annelida is Nephridia.
Nephridia are specialized excretory organs found in annelids, which are segmented worms. They play a crucial role in eliminating metabolic wastes from the body. Here is a detailed explanation of this unique characteristic:
1. Definition: Nephridia are tubular structures that function as excretory organs in annelids. They are responsible for filtering waste materials from the coelomic fluid and removing them from the body.
2. Structure: Nephridia are composed of a coiled tubule that opens into a nephrostome, which is a ciliated funnel-like structure. The tubule extends throughout the body segments of the annelid and ends in a nephridiopore, where the waste products are eliminated.
3. Function: Nephridia filter waste materials, such as nitrogenous compounds and excess salts, from the coelomic fluid. These waste products are then transported through the tubule and eliminated through the nephridiopore.
4. Role in osmoregulation: In addition to excretion, nephridia also play a role in osmoregulation. They help regulate the water and salt balance in the body by selectively reabsorbing or excreting these substances.
5. Variations: Nephridia can vary in structure and complexity among different species of annelids. Some annelids may have simple nephridia, while others may have more complex structures with additional functions, such as respiration and reproduction.
In conclusion, the unique characteristic of annelida is the presence of nephridia, specialized excretory organs that play a crucial role in eliminating waste materials from the body and regulating osmoregulation.

Explanation:
To answer this question, we need to understand the importance of the skin in the survival of pheretima (earthworms).
1. Importance of the skin:
- The skin of pheretima plays a crucial role in respiration, as earthworms do not have lungs.
- Earthworms breathe through their skin, which is moist and permeable to gases.
- Oxygen from the environment diffuses through their skin into their bloodstream, while carbon dioxide diffuses out.
2. Effects of skin drying:
- When the skin of pheretima dries out, it becomes less permeable to gases.
- This inhibits the exchange of oxygen and carbon dioxide, leading to a condition called asphyxia.
- Asphyxia is a state of oxygen deprivation that can ultimately lead to the death of the earthworm.
3. Dehydration vs. Starvation:
- Dehydration (option A) is the process of losing water from the body. While drying of the skin can contribute to dehydration, the primary concern is the disruption of gas exchange rather than water loss.
- Starvation (option B) refers to the lack of food. Skin drying does not directly lead to starvation.
Conclusion:
Therefore, if the skin of pheretima dries, it will die due to asphyxia (option C) caused by the inability to exchange gases through the skin.

The most common earthworm of India is Pheretima posthuma.
Explanation:
- Earthworms are segmented worms that belong to the phylum Annelida.
- They play a crucial role in improving soil fertility and nutrient cycling.
- In India, the most common earthworm species is Pheretima posthuma.
- Pheretima posthuma is also known as the Indian blue earthworm or common earthworm.
- It is widely distributed throughout India and can be found in various habitats, including agricultural fields, gardens, and forests.
- Pheretima posthuma has a cylindrical body with numerous segments.
- It is reddish-brown in color and has a relatively large size, ranging from 15 to 20 centimeters in length.
- This earthworm species is well-adapted to burrowing in the soil and plays a significant role in improving soil structure and fertility.
- Pheretima posthuma feeds on organic matter, such as dead plant material, and helps in the decomposition process.
- It also enhances nutrient availability in the soil through its excreta, known as vermicompost, which is rich in essential plant nutrients.
- Due to its ecological importance and abundance, Pheretima posthuma is commonly used in vermicomposting and as a bait for fishing.
- Therefore, Pheretima posthuma is considered the most common earthworm species in India.

According to Darwin, one acre of land may contain about 50,000 earthworms.
Here is the detailed explanation:
1. Charles Darwin was a renowned naturalist who extensively studied the behavior and ecology of various organisms, including earthworms.
2. Earthworms are vital for soil health as they help in the decomposition of organic matter, nutrient cycling, and soil structure improvement.
3. Darwin conducted several experiments and observations to estimate the population density of earthworms in different ecosystems.
4. Through his research, he found that the average population density of earthworms in one acre of land is around 50,000.
5. It is important to note that the actual number of earthworms may vary depending on various factors such as soil type, environmental conditions, and management practices.
6. Earthworm populations tend to be higher in fertile soils with abundant organic matter and favorable moisture levels.
7. Darwin's estimation of 50,000 earthworms per acre provides a general guideline for understanding the potential abundance of earthworms in an ecosystem.
8. The presence of a large population of earthworms in the soil indicates a healthy and fertile soil ecosystem.
In conclusion, according to Darwin, one acre of land may contain approximately 50,000 earthworms. This estimation is based on his extensive research and observations on earthworm populations in different ecosystems.

Excretory organs of an earthworm are:
The excretory system of an earthworm is responsible for removing metabolic waste from its body. The main excretory organs in an earthworm are nephridia.
Nephridia:
- Nephridia are the primary excretory organs in earthworms.
- They are present in pairs throughout the length of the body.
- Each segment of the earthworm's body contains a pair of nephridia.
- Nephridia function like small kidneys, filtering waste products from the coelomic fluid and excreting them out of the body.
- They help in the removal of nitrogenous waste, such as urea and ammonia, from the body.
Other excretory organs found in different organisms, but not in earthworms, include:
Malpighian tubules:
- Malpighian tubules are found in insects and some other arthropods.
- They are responsible for removing metabolic waste and excess water from the hemolymph (insect blood).
- Malpighian tubules actively transport waste products, such as uric acid, from the hemolymph into the digestive system for elimination.
Green glands:
- Green glands, also known as antennal glands, are excretory organs found in many crustaceans, such as crabs and lobsters.
- They remove waste products, such as ammonia and urea, from the hemolymph and excrete them out of the body.
- Green glands are located in the head region, behind the eyes, and are connected to the antennae.
Flame cells:
- Flame cells are excretory cells found in flatworms, such as planarians.
- They are responsible for removing metabolic waste and excess water from the body.
- Flame cells have a tuft of cilia that create a flickering flame-like appearance, hence their name.
- They help in the excretion of nitrogenous waste, such as ammonia, from the body.
In conclusion, the excretory organs of an earthworm are primarily nephridia. Nephridia function as the earthworm's excretory system, removing waste products from the coelomic fluid and excreting them out of the body.

Blood Pigment of Annelida:
The blood pigment of annelida refers to the substance responsible for oxygen transport in the blood of annelids, which are segmented worms. The correct answer is option C: Haemoglobin. Here are the reasons why Haemoglobin is the blood pigment of annelida:
1. Haemoglobin:
- Haemoglobin is a protein-based pigment found in the red blood cells of many animals, including annelids.
- It is responsible for binding and carrying oxygen from the respiratory organs or gills to the body tissues.
- Haemoglobin gives blood its red color when oxygenated and a darker shade when deoxygenated.
2. Haemocyanin:
- Haemocyanin is the blood pigment found in some invertebrates, such as mollusks and arthropods, but not annelids.
- Unlike haemoglobin, haemocyanin uses copper ions to bind and transport oxygen.
3. Haemanin and Cyanin:
- Haemanin and Cyanin are not recognized as blood pigments in annelids or any other organisms.
In conclusion, the correct blood pigment of annelida is Haemoglobin (option C). It is worth noting that different organisms may have different types of blood pigments depending on their evolutionary adaptations and physiological requirements.