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Questions and Answers
What is the definition of torsion in mollusks?
What is the result of torsion in terms of body symmetry?
What is the direction of the aperture in a twisted shell?
What type of torsion is found in most gastropods?
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What is one of the adaptations of the twisted body plan in mollusks?
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What is one of the functions of the coiled shell in mollusks?
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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.