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Mollusca: Torsion in Gastropods and Cephalopods
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Mollusca: Torsion in Gastropods and Cephalopods

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Questions and Answers

What is the definition of torsion in mollusks?

  • The coiling of the shell in a spiral manner
  • The 180° rotation of the head and foot during embryonic development
  • The asymmetry in the body plan of mollusks
  • The twisting of the visceral mass relative to the foot and shell (correct)
  • What is the result of torsion in terms of body symmetry?

  • Radial symmetry
  • Bilateral symmetry
  • Asymmetry (correct)
  • No symmetry
  • What is the direction of the aperture in a twisted shell?

  • Facing diagonally
  • Facing downwards (correct)
  • Facing sideways
  • Facing upwards
  • What type of torsion is found in most gastropods?

    <p>Complete torsion</p> Signup and view all the answers

    What is one of the adaptations of the twisted body plan in mollusks?

    <p>Protection of internal organs and head</p> Signup and view all the answers

    What is one of the functions of the coiled shell in mollusks?

    <p>Efficient feeding and burrowing behaviors</p> Signup and view all the answers

    Study Notes

    Torsion in Mollusca

    Torsion is a unique body plan characteristic found in mollusks, particularly in gastropods (snails and slugs) and some cephalopods (squids and octopuses).

    Definition:

    Torsion refers to the twisting of the visceral mass (containing the internal organs) relative to the foot and shell in mollusks.

    Key Features:

    • 180° rotation: The visceral mass rotates 180° during embryonic development, resulting in the anus and mantle cavity being located above the head and foot.
    • Asymmetry: Torsion leads to asymmetry in the body, with the left side of the body being more developed than the right side.
    • Coiling: The shell coils in a spiral manner, with the aperture (opening) facing downwards.

    Types of Torsion:

    • Complete torsion: Found in most gastropods, where the visceral mass rotates 180°.
    • Incomplete torsion: Found in some cephalopods, where the visceral mass rotates less than 180°.
    • Pseudo-torsion: Found in some mollusks, where the visceral mass does not rotate, but the body appears twisted due to other developmental processes.

    Adaptations:

    • Protection: The twisted body plan provides protection for the internal organs and the head.
    • Feeding: The coiled shell allows for efficient feeding and burrowing behaviors.
    • Locomotion: The twisted body plan enables efficient movement and maneuverability.

    Evolutionary Significance:

    • Convergent evolution: Torsion has evolved independently in different mollusk lineages, indicating its importance for survival and adaptation.
    • Diversification: Torsion has contributed to the diversification of mollusk body plans and the development of unique characteristics.

    Torsion in Mollusca

    • Torsion is a unique body plan characteristic found in mollusks, particularly in gastropods and some cephalopods.

    Definition and Process

    • Torsion refers to the twisting of the visceral mass relative to the foot and shell in mollusks.
    • During embryonic development, the visceral mass rotates 180°, resulting in the anus and mantle cavity being located above the head and foot.

    Characteristics

    • Asymmetry: Torsion leads to asymmetry in the body, with the left side of the body being more developed than the right side.
    • Coiling: The shell coils in a spiral manner, with the aperture (opening) facing downwards.

    Types of Torsion

    • Complete torsion: Found in most gastropods, where the visceral mass rotates 180°.
    • Incomplete torsion: Found in some cephalopods, where the visceral mass rotates less than 180°.
    • Pseudo-torsion: Found in some mollusks, where the visceral mass does not rotate, but the body appears twisted due to other developmental processes.

    Adaptations and Functions

    • Protection: The twisted body plan provides protection for the internal organs and the head.
    • Feeding: The coiled shell allows for efficient feeding and burrowing behaviors.
    • Locomotion: The twisted body plan enables efficient movement and maneuverability.

    Evolutionary Significance

    • Convergent evolution: Torsion has evolved independently in different mollusk lineages, indicating its importance for survival and adaptation.
    • Diversification: Torsion has contributed to the diversification of mollusk body plans and the development of unique characteristics.

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    Description

    Learn about torsion, a unique body plan characteristic found in mollusks, particularly in gastropods and some cephalopods. Discover how it affects the visceral mass and other body parts.

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