Septal Nephridia of Earthworm: Structure, Function, FAQs, & MCQs

 

Septal Nephridia of Earthworm: Structure and Function 

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Question: Write a short note on Septal Nephridia of Earthworm.

        

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What is Septal Nephridia? 

Answer:

The Septal Nephridia are the largest of nephridia in earthworms.

Location 

Septal Nephridia of Earthworm are present in segment 15th attached to both the faces of the intersegmental septum.

Structure of Septal Nephridia:

Septal Nephridia of Earthworm Diagram 

           

*Note: Refer and compare to the diagram for a better understanding of the topic. A well-labelled diagram is provided to enhance and make it easy to understand the write-up.

In earthworms, the anatomical structure of Septal Nephridia shows three main parts. They are: 

1. Nephrostome, 2. Body, 3. Terminal duct.

1. Nephrostome:

  Nephrostome diagram 

It is a ciliated funnel communicating with the coelom.

It is like an elliptical core bounded by the upper and lower lip.

The upper lip is formed of large central cells and 8 to 9 marginal cells whereas, the lower lip is formed of 4 to 5 compact cells. All of these cells are ciliated.

2. Body:

The main body of the nephridium is connected to the nephrostome by a short, narrow and ciliated tube-like neck.

The body has two main parts a short straight lobe and a long twisted lobe with a narrow apical part.

The twisted lobe has a proximal limb and a distal limb which are twisted with each other and the proximal limb is joined to the neck.

3. Terminal duct:

The distal limb of the body of nephridia continues as a short and narrow duct called the terminal duct.

Terminal ducts of septal nephridia of earthworms open into a pair of septal excretory canals, then through supra-intestinal excretory ducts, it opens finally into the intestine.

Nephridial Tubule:

The glandular mass of nephridia is traversed by a coiled tubule having four ciliated tracts one each in the neck and terminal duct, two in the body. 

There are four parallel tubules in the straight lobe, 3 tubules in the basal part, and 2 in the apical part of each limb of the twisted loop. Also one each in neck and terminal duct.

2. Arrangement :

Arrangement of Septal Nephridia of Earthworm on a septum Diagram

Each septum behind the 15th segment has 4 rows of septal nephridia. Two of them are faced anteriorly and two posteriorly.

Each row may contain 20-25 nephridia making them around 80-100 in total in each septum.

These nephridia remain freely suspended in the coelom of the segment while their terminal ducts then open up into a pair of septal excretory canals. 

These canals run parallel to the commissural vessel of their side, inwards along the posterior face of the septum, one on each side.

They pour their content dorsally into a pair of supra-intestinal excretory ducts which are present side by side mid-dorsally just above the intestine.

The intestinal excretory ducts run beneath the dorsal blood vessel from the 15th to the last segment.

They open into the intestine in each segment via narrow ductules having sphincter openings.

Septal Nephridia function:

Nephridia are abundantly provided by blood vessels. Septal nephridia eliminates excretory material from the blood and coelomic fluid.

Related important questions :

Question: 

Difference between septal Nephridia and pharyngeal nephridia :

Answer:

1. Location:

*Septal Nephridia are present attached to both the inter-segmental septum behind the 15th segment.

*Pharyngeal Nephridia are present on either side of the pharynx and oesophagus in the 4th, 5th and 6th segment 

2. Nephrostome:

*Septal nephridia opens in the coelom of its segment by nephrostome.

*Pharyngeal nephridia lack nephrostome. ( Note:  Integumentary nephridia also lack nephrostome.)

3. Function:

*Septal Nephridia eliminate excretory waste from the blood and coelomic fluid.

*Pharyngeal Nephridia eliminates excretory waste from the blood.

4. Number:

*Number of septal nephridia varies from 80 to 100 in the 15th segment.

*Only 3 pairs of pharyngeal nephridia in the 4th, 5th and 6th segments.

Multiple choice questions (MCQs) related to Nephridia

1. exonephric nephridia of earthworm is.

• a. septal
• b. pharyngeal
• c. integumentary 
• d. all of these

Answer:

c. integumentary

2. The nephridia found most in number are:

• a. septal
• b. pharyngeal
• c. integumentary
• d. oesophageal

Answer:

c. integumentary

3. Septal nephridia are:

• a. respiratory function
• b. excretory in function
• c. circulatory function
• d. nervous in function

Answer:

b. excretory in function

4. The excretory product of earthworms is:

• a. ammonia
• b. uric acid
• c. urea
• d. ammonia and urea

Answer:

d. ammonia and urea

5. In earthworms nephrostome is absent in:

• a. septal nephridia
• b. pharyngeal nephridia
• c. integumentary nephridia and pharyngeal nephridia
• d. all of them

Answer:

c. integumentary nephridia and pharyngeal nephridia

6. Nephridia of earthworms are:

• a. absent in the first three segments
• b. for excretion
• c. for osmoregulation
• d. all of these

Answer:

d. all of these

7. Which is not enteronephric nephridia of earthworm?

• a.  integumentary
• b. pharyngeal
• c. septal
• d. both a. and b.

Answer:

a. integumentary

8. Pharyngeal nephridia of earthworms are located in segments:

• a. 6,7,8
• b.7,8,9
• c. 3,4,5
• d. 4,5,6

Answer:

d. 4,5,6

9. In earthworms, exonephric excretion takes place by:

• a. septal nephridia 
• b. pharyngeal nephridia 
• c.integumentary nephridia 
• d. all of these

Answer: 

c. integumentary nephridia 

10. Enteronephric nephridia of earthworm opens into:

• a. coelom
• b. body surface
• c. intestine 
• d. stomach

Answer:

c. intestine

11. The septal nephridia of Pheretima expel their waste into:

• a. coelom
• b. blood
• c. pharynx
• d. intestine 

Answer:

d. intestine

12. Which of the following statements is not correct with respect pharyngeal nephridia of Pheretima:

• a. They are present in 3 paired groups
• b. one pair group of these nephridia lies in each of the segments 4-6
• c. they are exonephric
• d. they are without nephrostomes

Answer:

 c. they are exonephric 

13. "Forest of nephridia" present in the region of:

• a. preclitellar
• b. cliteller
• c. postcliteller

Answer:

b. cliteller

Next important topics related to Earthworm:

Digestive System of Earthworm