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Questions and Answers
What is the function of the mucin secretion by the pharyngeal glands?
What is the function of the mucin secretion by the pharyngeal glands?
The gizzard is responsible for the chemical digestion of food.
The gizzard is responsible for the chemical digestion of food.
False
Name one enzyme found in the intestinal digestive juices and its function.
Name one enzyme found in the intestinal digestive juices and its function.
Lipase; it splits fat.
The end products of digestion are absorbed by the _______ of the intestine.
The end products of digestion are absorbed by the _______ of the intestine.
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What is one role of the septal nephridia?
What is one role of the septal nephridia?
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Match the following digestive enzymes with their functions:
Match the following digestive enzymes with their functions:
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Pharyngeal nephridia are equipped with nephrostome.
Pharyngeal nephridia are equipped with nephrostome.
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What happens to undigested food in the digestive system?
What happens to undigested food in the digestive system?
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Which part of the earthworm's digestive system is primarily responsible for protein digestion?
Which part of the earthworm's digestive system is primarily responsible for protein digestion?
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The gizzard in an earthworm is located in the segments 14 to 16.
The gizzard in an earthworm is located in the segments 14 to 16.
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What are the three regions of the intestine in an earthworm?
What are the three regions of the intestine in an earthworm?
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The _______ opens into the gizzard and extends from the 9th to the 14th segments.
The _______ opens into the gizzard and extends from the 9th to the 14th segments.
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Match the following components of the earthworm's digestive system with their primary function:
Match the following components of the earthworm's digestive system with their primary function:
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Where is the anus located in the digestive system of the earthworm?
Where is the anus located in the digestive system of the earthworm?
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The intestinal caeca in an earthworm are devoid of vascular structures.
The intestinal caeca in an earthworm are devoid of vascular structures.
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What types of food do earthworms typically consume?
What types of food do earthworms typically consume?
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What is the primary function of integumentary nephridia?
What is the primary function of integumentary nephridia?
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Each segment of the body contains about 500 nephridia.
Each segment of the body contains about 500 nephridia.
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Name the two types of nephridia mentioned in the content and their respective excretion types.
Name the two types of nephridia mentioned in the content and their respective excretion types.
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The nerve ring is formed by a pair of _______ ganglia lying in the third segment.
The nerve ring is formed by a pair of _______ ganglia lying in the third segment.
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How many pairs of nerves arise from the cerebral ganglia as part of the peripheral nervous system?
How many pairs of nerves arise from the cerebral ganglia as part of the peripheral nervous system?
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Match the following components of the nervous system with their descriptions:
Match the following components of the nervous system with their descriptions:
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The sympathetic nervous system is included directly in the central nervous system.
The sympathetic nervous system is included directly in the central nervous system.
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What do septal nephridia collect from the coelomic cavity?
What do septal nephridia collect from the coelomic cavity?
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Study Notes
Phylum: Annelida
- Annelida is a phylum of segmented worms.
- Annulus means ring, eidos means form.
Classification
- Phylum: Annelida
- Class: Oligochaeta
- Genus: Pheretima
- Species: posthuma
Habit and Habitat
- Pheretima is a common Indian earthworm found in moist places.
- They are abundant during the rainy season.
- The presence of earthworms is indicated by their characteristic coiled castings.
- They burrow during the day and emerge at night to search for food.
External Features
- Pheretima has a long, cylindrical body (15-20 cm long, 0.3-0.5 cm wide).
- The dorsal surface is browner than the ventral surface.
- This coloration is due to porphyrin, a pigment formed from chlorophyll consumed by the earthworm.
Body Structure
- The body is segmented (100-120 segments).
- The anterior end has a mouth below a fleshy structure called the prostomium.
- The first segment surrounding the mouth is the peristomium.
- The dorsal surface has a dorsal blood vessel.
- The ventral surface has a ventral blood vessel.
Body Segments
- The intersegmental groove is the space between segments.
- Dorsal pores are found in the intersegmental groove, after 12 segments.
- Spermathecal pores, located in intersegmental grooves 5/6, 6/7, 7/8, and 8/9,
- Each segment has locomotory structures called setae, developed from a setigerous cell.
- The setae are curved in an 'S' shape, with a thicker middle part (nodule).
- Setae are absent in the first and last segments, as well as in the clitellum.
Clitellum
- Segments 14-16 are deep brown and thick-walled.
- This region is called the clitellum.
- The female genital opening is located on the ventral side of segment 14.
- Male genital openings are on the ventral side of segment 18.
- A pair of genital papillae are found on the ventral surface of segments 17 and 19.
- The anus is at the end of the last segment.
Digestive System
- The digestive system is a straight tube from the mouth to the anus.
- It consists of mouth, buccal cavity, pharynx, esophagus, gizzard, stomach, intestine, and anus.
- The digestive system is involved in food digestion and absorption.
- Parts of the digestive tract include the buccal chamber, pharynx, esophagus, gizzard, stomach, intestine, and intestinal caecum.
- Pre-typhlosolar region extends from segment 15 to 26.
- The typhlosolar region extends from segment 26 to 23–25 in front of the anus.
- The post-typhlosolar region is devoid of typhlosole.
- The anus is in the last segment.
Digestion
- Earthworms eat leaves, seeds, and soil.
- The buccal cavity is everted and the food is drawn into the mouth by the pharynx.
- Pharyngeal glands secrete a juice containing mucin and proteolytic enzymes.
- These lubricate the food and act on proteins.
- The food enters the gizzard, where it is ground by the muscular action of the gizzard wall.
- In the intestine, the food contacts digestive juices to convert proteins to peptones, starches to sugars and fats to split fat.
- The end products of digestion are absorbed into the blood and distributed throughout the body.
- Undigested food is expelled at intervals through the anus.
Excretory System
- The excretory organs are nephridia.
- They are coiled tubes found in all segments except the first three segments.
- There are three types: septal, pharyngeal and integumentary nephridia
- Glandular cells of the nephridia extract water and nitrogenous wastes from the blood (urea, ammonia, amino-acids)
- Nephridial contents are released in the alimentary canal.
- Water and other products are excreted along with faecal matter.
Nervous System
- The nervous system includes the central nervous system (CNS) and the peripheral nervous system (PNS).
- The CNS consists of a nerve ring and a double ventral nerve cord with paired ganglia.
- The nerve ring forms a brain-like structure (suprapharyngeal ganglia).
- The ventral nerve cord runs along the ventral side of the body.
- Ganglia are located in each segment.
- The peripheral nervous system consists of nerves that extend from the CNS to various parts of the body.
- Four giant fibers are present in the nerve cord, responsible for quick movements.
Reproductive System
- Earthworms are hermaphrodites (possess both male and female reproductive organs).
- Testes (paired) are situated in the 10th and 11th segments.
- Seminal vesicles are located in 11th and 12th segments.
- Spermatheca (paired) are located in segments 6-9 to receive sperms from another earthworm.
- Spermatic funnel collects sperms from the testes.
- Vas deferens is part of the reproductive system that carries sperm.
- The prostate gland secretes fluid for sperm mixture.
- Male genital pores are in the 18th segment.
- Ovaries are located in the 12th and 13th segments.
- Oviducts carry the eggs.
- Spermathecal pores are located in the intersegmental grooves of segments 5-9 to receive sperm from another earthworm.
- Copulation often occurs during rainy season.
Copulation and Cocoon
- Earthworms exchange sperms during copulation.
- A cocoon is formed from the clitellum and contains fertilized eggs.
- Fertilization is external.
- The cocoon is deposited in a moist environment.
Economic Importance
- Earthworms are:
- Used in agriculture as soil enrichers through castings.
- They help aerate soil and improve drainage.
- They are used as bait in fishing.
- They are used in laboratories as study organisms.
- They are used as food by some animals (lizards, birds).
- They were used as medicine in ancient times to treat various ailments.
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Description
Test your knowledge about the phylum Annelida, specifically the Oligochaeta class, featuring the common earthworm Pheretima posthuma. Explore their classification, habitat, external features, and body structure in this engaging quiz.
