Phylum Annelida : Class 11 Biology One Shot Notes for NEET

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Before diving into the Phylum Annelida : Class 11 Biology One Shot Notes for NEET, nsure you have gone through comprehensive guide on Phylum Aschelminthes (Roundworms): Characteristics, Classification & NEET Important MCQs

Table of content 

• Definition to Annelida
• ​General Characteristics of Annelids)
• ​Body Systems (Digestive, Excretory & Nervous)
• ​Locomotion in Earthworms, Nereis and Hirudinaria 
• ​Key Examples: Earthworms, Nereis, & Hirudinaria 
• ​Nervous system in Annelids
• ​NEET Previous Year Questions (PYQs) & Practice Test

Definition to Annelida 

• Annelids are first Coelomate, Triploblastic, bilateral symmetrical, metamerically segmented animals with organ system level of organisation.
• Annelids are well known for its metamerically segmented body. 
• In metamerically segmented body, external segments make correspondence to internal segments.

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General Characteristics of Annelids

• They are aquatic and found in marine and fresh water and also live in  terrestrial habitat.
• They are free-living some are parasite like Pontobdella, Acanthobdella etc.
• They have organ-system level of body organisation and bilateral symmetry. They are triploblastic, metameric segmented and coelomate animals. 

💡 Related study to understand the Phylum Platyhelminthes : General Characters, Classification and Example , Multiple Choice questions: NEET

• Their body surface is distinctly marked out into segments or metameres. Hence the phylum name Annelida has been given.
• They possess longitudinal and circular muscles which help in locomotion. 

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• Aquatic annelids like Nereis possess lateral appendages, parapodia, which help in swimming. 
• A closed circulatory system is present in which blood is flown in network of blood vessels.
• Nephridia  help in osmoregulation and excretion. 
• Nervous system consists of paired ganglia  connected by lateral nerves to a double ventral nerve cord. 
• Nereis is dioecious, but earthworms and leeches are monoecious. Reproduction is sexual.

🔼 Video Key Moments (Timestamps)

00:00 - Intro to Phylum Annelida

• 00:34 - Concept of Metamers & Metamerism
• 01:23 - Diagrammatic Study of Earthworm Segmentation
• 03:14 - Occurrence: Aquatic vs Terrestrial Habitat
• 05:13 - Level of Organization & Symmetry
• 06:14 - First time Coelomate animals
• 07:21 - Locomotion in Earthworm vs Nereis
• 08:25 - Parapodia: Special feature of Nereis
• 10:14 - Closed Circulatory System
• 10:40 - Excretion via Nephridia
• 11:24 - Nervous System & Nerve Cord
• 14:02 - Examples: Pheretima & Hirudinaria

Body Systems 

Digestive System

• ​Annelids possess a complete digestive tract (mouth to anus).
• ​Digestion occurs entirely outside the cells within the gut cavity.
• ​In many species, the system is specialized into regions like the pharynx, esophagus, crop, gizzard, and intestine for efficient food processing.

Excretory system by Nephridia:

• They use specialized tubular structures called Nephridia (singular: Nephridium) for excretion and Osmoregulation.
• These organs help in removing nitrogenous wastes and maintaining the salt-water balance in the body.

Nervous System 

• Brain & Nerve Cord: It consists of paired Cerebral Ganglia (acting as a simple brain) connected to a double ventral nerve cord.
• ​Segmental Ganglia: The nerve cord has swellings called ganglia in every segment, allowing for coordinated movement.
• ​Lateral Nerves: Paired nerves extend from the ganglia to the body wall and muscles in each segment.

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Locomotion in Earthworms, Nereis 

and Hirudinaria 

Earthworms:

• They move using a combination of muscle contractions and tiny, S-shaped chitinous bristles called Setae. 
• The coordinated action of circular and longitudinal muscles allows them to crawl through the soil.

​Nereis (Aquatic Annelid): 

• Being aquatic, Nereis possesses lateral, fleshy appendages called Parapodia. 
• These structures act like paddles, helping the organism in swimming and active movement.

​Hirudinaria (Leech): 

• Leeches move using a characteristic "Looping" movement on solid surfaces with the help of Anterior and Posterior Suckers.
• In water, they perform graceful, undulating swimming movements.

Examples of Annelida  

Nereis

• It is commonly called as Calm worm or Rag worm.
• Prostomium and Peristomium are two parts of Head of Nereis. First one is triangular and second one is ring like.

Nereis ( Calm worm)

• Mouth is located at anterior of Peristomium with fine tentacles.
• It use parapodia for locomotion and swimming.
• It usually live in burrow of sand and carnivores and nocturnal in nature.

  🩺 NEET Important Point

  Annelida are the first animals to have a True Coelom and a Closed Circulatory System. Many times NEET asks about 'Nephridia'—remember it helps in both excretion and osmoregulation!

   
• It can maintain its internal body environment with respect to surrounding.
• Alimentary canal is in form of straight tube and include mouth to rectum.

💡 Related study to understand the Phylum Porifera (Sponges) NCERT Notes & MCQs for NEET Biology

• The number of body segments are 200. 
• It has four pairs of simple and round eyes.
• It reproduce sexually because it is dioecious. Male and female are different.

 Pheretima 

• It is commonly called as Earth worm.
• Earthworms have microscopic  fine hair like structure  called setae that help in locomotion and Anchorage. Setae are present in body except first, last and clitellum region.
• Earthworms have a closed circulatory system with a heart, capillaries, and vessels. Their blood is red and contains hemoglobin which is dissolved in plasma.
• Earthworms have a dark band of glandular tissue called the clitellum, which is located between 14th and 16th segment. Clitellum has  mature eggs of Earthworm.

Pheretima (Earthworm) 

• Earthworms have blood glands in segments 4-6 that produce hemoglobin and blood corpuscles.
• Earthworms are hermaphrodites or Monoecious . They have both male and female sex organs.
• Earthworms have nephridia that help them excrete nitrogenous waste and regulate osmoregulation.
• Alimentary canal is in form of straight tube and include mouth to rectum.

Feature	Nereis	Earthworm (Pheretima)
Habitat	Aquatic (Marine)	Terrestrial (Moist Soil)
Locomotion	Parapodia	Setae & Muscles
Reproduction	Dioecious (Separate)	Monoecious (Hermaphrodite)

 Hirudinaria

• It is commonly called Leech. Leeches has  an anterior sucker at the front of the body and a posterior sucker at the back of the body.
• The number of body segments are 33.

💡 Related study to understand Phylum Aschelminthes (Roundworms): Characteristics, Classification & NEET Important MCQs

• Leech are hermaphrodites or Monoecious . They have both male and female sex organs.
• Skin is kept moist and slimy due to abundant mucus secretion
• Body is divided into cephalic, pre clittellar, clittellar, middle, caudal and posterior sucker.

Hirudinaria (Leech)

• Anterior sucker is oval and contains ventral tri radiate mouth formed by the fusion prostomium and few anterior segments. 
• The posterior sucker is highly muscular and acts as powerful locomotory and adhesive organ.
• Eyes are  5 pairs dorsally. 
• It is sanguivorous ectoparasite and release anti coagulant called Hirudin.

To understand   the  detail  information about the  Phylum Arthropoda: Class 11 Biology One Shot Notes for NEET  read my next detailed guide

🎯 NEET MULTIPLE CHOICE QUESTIONS

🔥 100% CHALLENGE

"Questions yahi se aayega... taiyari jeet ki!"

 1. Which of the following statement is not correct with respect to Annelida.

A.They are not  found in marine water.  

B. Some members  are found in fresh water.

C. Some of the members are Parasite.

D. Most of the members are free living. 

Answer : A  

2. Which one of following features first appeared  in members of Annelida.

A. Triploblastic

B. Bilateral symmetrical 

C. Organ system level of organisation 

D. Coelom 

Answer : D 

3. Name Annelida has been given due to which of the following features 

A. Nerve ring

B. Worm like body

C. Metameric segmentation 

D. All of the above.

Answer : C 

4. Metamerism in Annelids signify 

A. External segments make correspondence to internal segments.

B. Paired ganglia  are connected by lateral nerves to a double ventral nerve cord. 

C. Hemoglobin  is dissolved in plasma.

D. None of the above 

Answer : A 

5. Consider the following statement and select the correct code:

1.  Aquatic members of Annelids like Nereis  use appendages like parapodia for swimming and Locomotion. 

2. Terrestrial members of Annelids like Leech and Earthworm  use circular and longitudinal muscle for locomotion. 

A. Only 1   

B. Only 2

C. Neither 1 nor 2 

D. Both 1 and 2 

Answer : D 

6. Which one of the following is Excretory organ in Annelids.

A. Malpighian tubule 

B. Nephredia 

C. Proboscis glands 

D. Excretory pore

Answer : B

7. Which of the following statement is correct with respect to Annelida.

A. Closed circulatory system is present in which blood is flown in network of blood vessels.

B. Protonephridia  help in osmoregulation and excretion. 

C. Pseudopodia are lateral appendages in Nereis. 

D. Leech and Earthworm are Dioecious.

Answer : A  

8.Which one of the following statement is not correct with respect to nervous system in Annelids.

A. Supra oesophageal ganglia represents the brain.

B. It has paired ganglion.

C. Ganglion are connected by the lateral nerves.

D. Lateral nerves are finally connected with ventral double nerve cord.

Answer : A   

9. Consider the following characteristics of Annelids in which they constitute nervous system and select the correct code

1. Unpaired  ganglion 

2. Paired   ganglion  

3. Lateral nerves 

4. Ventral Double nerve cord

5. Dorsal Single nerve cord

A. 2, 3 and 4

B. 1, 3 and 5

C. 1, 4 and 5

D. 2, 4 and 5

Answer : A 

10. Which of the following statement is correct.

A. sexual  reproduction is present in Annelids.

B. Leech and Earth worm are Hermaphrodite.

C. Nereis is Dioecious 

D. All of the above.

Answer : D 

11. Which one of following is not a Annelids.

A. Earthworm (Pheretima)

B. Leech ( Hirudinaria)

C. Silver fish ( Lepisma)

D. Calm worm ( Nereis) 

Answer : C 

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