Phylum Annelida includes a diverse group of organisms commonly known as segmented worms. This phylum is characterized by a range of anatomical and physiological features that distinguish it from other phyla.
Characteristics of Phylum Annelida (Kingdom Animalia)
- Habitat: Annelids can be found in various environments. They may be aquatic, inhabiting marine and freshwater ecosystems, or terrestrial, living on land. Some annelids are free-living, while others are parasitic.
- Body Organization: Annelids exhibit an organ-system level of body organization, meaning their bodies are made up of various organs that perform specific functions.
- Symmetry: They possess bilateral symmetry, allowing for a streamlined body shape and efficient movement.
- Tissue Layers: Annelids are triploblastic, meaning they have three germ layers: ectoderm, mesoderm, and endoderm.
- Segmentation: Their bodies are divided into segments, known as metameres, which are clearly marked. This segmentation is a distinctive feature of this phylum and gives the group its name (Latin: annulus, meaning "little ring").
- Coelom: Annelids are coelomate animals, possessing a true coelom, which is a fluid-filled body cavity lined with mesoderm.
Locomotion and Musculature
- Muscles: Annelids have well-developed longitudinal and circular muscles that aid in locomotion. These muscles work in coordination to enable the worm to move efficiently.
- Parapodia: Aquatic annelids, such as Nereis, have lateral appendages called parapodia, which assist in swimming.
Circulatory and Excretory Systems
- Circulatory System: Annelids have a closed circulatory system, meaning their blood is contained within vessels. This system is more efficient than an open circulatory system, allowing for better transport of nutrients and gases.
- Nephridia: These are excretory organs that help in osmoregulation and the removal of metabolic waste products.
Nervous System
- Neural Organization: The nervous system of annelids consists of paired ganglia (clusters of nerve cells) connected by lateral nerves to a double ventral nerve cord. This structure allows for efficient coordination of body movements and responses to environmental stimuli.
Reproduction
- Dioecious and Monoecious Species: Some annelids, like Nereis, are dioecious (having separate male and female individuals), while others, like earthworms and leeches, are monoecious (having both male and female reproductive organs in the same individual).
- Sexual Reproduction: Reproduction in annelids is primarily sexual, involving the exchange of genetic material between individuals.
Examples
- Nereis: An aquatic form known for its parapodia.
- Pheretima (Earthworm): A terrestrial annelid that plays a crucial role in soil aeration and fertility.
- Hirudinaria (Leech): A blood-sucking parasitic form often found in freshwater habitats.
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| Source: NCERT |
Plant Kingdom - NOTES and MCQs
FAQs
Q1: What are the primary habitats of annelids?
A1: Annelids can be found in aquatic (marine and freshwater) and terrestrial environments. They can be free-living or parasitic.
Q2: How is the body of annelids organized?
A2: Annelids exhibit an organ-system level of body organization, bilateral symmetry, are triploblastic, metamerically segmented, and coelomate.
Q3: What role do parapodia play in annelids?
A3: In aquatic annelids like Nereis, parapodia are lateral appendages that assist in swimming.
Q4: How do annelids achieve locomotion?
A4: Annelids use longitudinal and circular muscles for locomotion. These muscles work together to enable movement.
Q5: What kind of circulatory system do annelids have?
A5: Annelids have a closed circulatory system, which is more efficient for transporting nutrients and gases.
Q6: What is the function of nephridia in annelids?
A6: Nephridia help in osmoregulation and excretion of metabolic wastes.
Q7: How is the nervous system of annelids structured?
A7: The nervous system consists of paired ganglia connected by lateral nerves to a double ventral nerve cord.
Q8: Are annelids dioecious or monoecious?
A8: Some annelids, like Nereis, are dioecious, while others, like earthworms and leeches, are monoecious.
Q9: What type of reproduction is seen in annelids?
A9: Annelids primarily reproduce sexually.
Q10: Can you name some common examples of annelids?
A10: Common examples include Nereis, Pheretima (Earthworm), and Hirudinaria (Leech).
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Multiple Choice Questions (MCQs)
What type of body symmetry do annelids exhibit?
- A) Radial
- B) Bilateral
- C) Asymmetrical
- D) None of the above
Annelids are primarily:
- A) Diploblastic
- B) Triploblastic
- C) Monoblastic
- D) None of the above
What structure assists in locomotion in aquatic annelids like Nereis?
- A) Parapodia
- B) Nephridia
- C) Setae
- D) Gills
Which system in annelids is closed?
- A) Respiratory system
- B) Circulatory system
- C) Digestive system
- D) Excretory system
What role do nephridia play in annelids?
- A) Digestion
- B) Respiration
- C) Osmoregulation and excretion
- D) Reproduction
The nervous system of annelids consists of:
- A) Brain and spinal cord
- B) Paired ganglia and double ventral nerve cord
- C) Nerve net
- D) None of the above
Which of the following is a monoecious annelid?
- A) Nereis
- B) Earthworm
- C) Hirudinaria
- D) both B and C
What is the main function of longitudinal and circular muscles in annelids?
- A) Digestion
- B) Locomotion
- C) Respiration
- D) Reproduction
Which of the following annelids is known for being parasitic?
- A) Nereis
- B) Earthworm
- C) Hirudinaria
- D) None of the above
What type of reproduction is found in annelids?
- A) Asexual
- B) Sexual
- C) Binary fission
- D) Budding
Answers to MCQs
- B) Bilateral
- B) Triploblastic
- A) Parapodia
- B) Circulatory system
- C) Osmoregulation and excretion
- B) Paired ganglia and double ventral nerve cord
- D) both B and C
- B) Locomotion
- C) Hirudinaria
- B) Sexual
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