Phylum – Echinodermata: Detailed Notes and MCQs

Introduction

The phylum Echinodermata consists of fascinating marine animals known for their distinctive spiny body structure. Exclusively marine, these creatures exhibit an organ-system level of organization. The term "Echinodermata" is derived from the Greek words "echinos" (spiny) and "derma" (skin), highlighting their unique appearance.

Key Characteristics of Echinodermata (Kingdom Animalia)

• Habitat: Exclusively marine
• Body Organization: Organ-system level
• Symmetry:
  • Adult: Radially symmetrical
  • Larvae: Bilaterally symmetrical
• Tissue Layers: Triploblastic
• Body Cavity: Coelomate
• Endoskeleton: Composed of calcareous ossicles
• Digestive System: Complete, with the mouth on the lower (ventral) side and anus on the upper (dorsal) side

Unique Features

• Water Vascular System:
  • Functions: Essential for locomotion, food capture, transport, and respiration.
  • Structure: Composed of a network of hydraulic canals.
• Excretory System: Absent

Reproduction

• Sexes: Separate (dioecious)
• Reproduction: Sexual
• Fertilization: Usually external
• Development: Indirect, with free-swimming larvae

Examples of Echinoderms

1. Asterias (Starfish)
2. Echinus (Sea Urchin)
3. Antedon (Sea Lily)
4. Cucumaria (Sea Cucumber)
5. Ophiura (Brittle Star)

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Asterias (Starfish)

Habitat

Starfish inhabit marine environments, commonly found in shallow waters on rocky shores, coral reefs, and seagrass beds.

Physical Characteristics

• Central disc with five radiating arms (some species have more).
• Surface covered with small spines and pedicellariae (pincer-like structures).
• Exhibit radial symmetry as adults.

Body Structure

• Endoskeleton: Composed of calcareous ossicles.
• Water Vascular System: Facilitates locomotion, feeding, and respiration.
• Tube Feet: Located on the underside of the arms for movement and prey handling.

Feeding

Starfish are carnivorous, primarily feeding on mollusks like clams and oysters. They use tube feet to pry open shells and evert their stomachs to digest prey externally.

Reproduction

Starfish reproduce sexually, with separate sexes (dioecious). Fertilization occurs externally, and they undergo indirect development with free-swimming larval stages.

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Echinus (Sea Urchin)

Habitat

Sea urchins thrive in marine environments, ranging from shallow waters to deep ocean floors.

Physical Characteristics

• Globular shape with long, movable spines covering the body.
• Exhibit radial symmetry with a hard calcareous shell known as a test.
• The mouth is located on the underside, featuring Aristotle's lantern, a specialized feeding structure.

Body Structure

• Endoskeleton: Composed of rigid calcareous plates.
• Water Vascular System: Extends into tube feet for locomotion and food handling.
• Spines: Provide protection and assist in movement.

Feeding

Herbivorous, primarily feeding on algae and detritus. Sea urchins use Aristotle's lantern to scrape algae from surfaces.

Reproduction

Sea urchins exhibit sexual reproduction with separate sexes. Fertilization is external, and they undergo indirect development with planktonic larval stages.

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Antedon (Sea Lily)

Habitat

Sea lilies are typically found in marine environments, often attached to the seabed or floating in the water column.

Physical Characteristics

• Central disc with numerous feathery arms (usually 10).
• Arms are highly branched and serve for filter feeding.

Body Structure

• Endoskeleton: Composed of calcareous plates supporting the body.
• Water Vascular System: Used for movement and feeding.
• Cirri: Small, grasping appendages used to anchor themselves to substrates.

Feeding

As suspension feeders, sea lilies capture plankton and detritus from the water using their feathery arms.

Reproduction

Sea lilies reproduce sexually, with separate sexes. Fertilization is external, and they undergo indirect development with free-swimming larvae.

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Cucumaria (Sea Cucumber)

Habitat

Sea cucumbers are typically found on the seabed in both shallow and deep marine environments.

Physical Characteristics

• Elongated, soft-bodied animals resembling cucumbers.
• Mouth and anus located at opposite ends of the body.
• Tube feet arranged in rows along the body.

Body Structure

• Endoskeleton: Reduced, with small calcareous ossicles embedded in the body wall.
• Water Vascular System: Utilized for movement and feeding.
• Tentacles: Surround the mouth and are used for food capture.

Feeding

Sea cucumbers are detritivores, feeding on organic matter and small particles in the sediment. They use their tentacles to sift through the substrate and bring food to their mouths.

Reproduction

Sea cucumbers exhibit sexual reproduction with separate sexes. Fertilization is external, and they undergo indirect development with planktonic larvae.

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Ophiura (Brittle Star)

Habitat

Brittle stars inhabit marine environments, from shallow waters to deep ocean floors.

Physical Characteristics

• Central disc with long, slender, flexible arms.
• Arms are used for rapid movement and can regenerate if broken.

Body Structure

• Endoskeleton: Comprised of calcareous ossicles.
• Water Vascular System: Facilitates locomotion and feeding.
• Tube Feet: Located on the underside of the arms, but lack suckers.

Feeding

Brittle stars are omnivorous, feeding on detritus, small invertebrates, and plankton. They use their arms to capture food and bring it to their mouths.

Reproduction

Brittle stars reproduce sexually, with separate sexes. Fertilization is external, and they undergo indirect development with planktonic larvae.

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FAQs

1. What type of habitat do echinoderms occupy?
   Echinoderms are exclusively marine.

2. What kind of body symmetry do echinoderms exhibit in their adult form?
   Adult echinoderms exhibit radial symmetry.

3. How do larvae of echinoderms differ in terms of symmetry?
   Larvae of echinoderms exhibit bilateral symmetry.

4. What is the most distinctive feature of echinoderms?
   The most distinctive feature of echinoderms is the presence of a water vascular system.

5. What are the functions of the water vascular system in echinoderms?
   The water vascular system aids in locomotion, food capture and transport, and respiration.

6. Do echinoderms have an excretory system?
   No, echinoderms do not have an excretory system.

7. How do echinoderms reproduce?
   Echinoderms reproduce sexually.

8. What type of fertilization is seen in echinoderms?
   Echinoderms usually have external fertilization.

9. What kind of development is observed in echinoderms?
   Echinoderms undergo indirect development with free-swimming larvae.

10. Can you name some examples of echinoderms?
    Examples of echinoderms include Asterias (Starfish), Echinus (Sea Urchin), Antedon (Sea Lily), Cucumaria (Sea Cucumber), and Ophiura (Brittle Star).

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Multiple-Choice Questions (MCQs)

1. What type of symmetry do adult echinoderms exhibit?

   a) Radial
   b) Bilateral
   c) Asymmetrical
   d) None of the above

2. What is the main function of the water vascular system in echinoderms?

   a) Reproduction
   b) Feeding
   c) Locomotion
   d) Excretion

3. Which of the following is absent in echinoderms?

   a) Digestive system
   b) Circulatory system
   c) Excretory system
   d) Respiratory system

4. Where is the mouth located in echinoderms?

   a) Dorsal side
   b) Ventral side
   c) Lateral side
   d) Posterior side

5. How do echinoderms respire?

   a) Through lungs
   b) Through gills
   c) Through water vascular system
   d) Through skin

6. What type of reproduction is observed in most of the echinoderms?

   a) Asexual
   b) Sexual
   c) Both a and b
   d) None of the above

7. What type of development is seen in echinoderms?

   a) Direct
   b) Indirect
   c) Both a and b
   d) None of the above

8. What type of skeleton do echinoderms have?

   a) Exoskeleton
   b) Endoskeleton
   c) Hydrostatic skeleton
   d) None of the above

9. How is fertilization typically carried out in echinoderms?

   a) Internally
   b) Externally
   c) Both a and b
   d) None of the above

10. Which of the following is an example of an echinoderm?

    a) Asterias
    b) Hydra
    c) Fasciola
    d) Taenia

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Answers to MCQs

1. a) Radial
2. c) Locomotion
3. c) Excretory system
4. b) Ventral side
5. c) Through water vascular system
6. b) Sexual
7. b) Indirect
8. b) Endoskeleton
9. b) Externally
10. a)

Also Read:

• NOTES: Class 11
• MCQs: Class 11