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Difficulty: MediumHigher Invertebrates: Annelida, Mollusca, Arthropoda, and Echinodermata

Unlike most other molluscs, members of the class Cephalopoda (such as squids and octopuses) exhibit which combination of physiological and anatomical adaptations?

  1. A closed circulatory system, a well-developed nervous system with image-forming eyes, and a foot modified into tentaclesAnswer
  2. B
    An open circulatory system, excretion via Malpighian tubules, and a heavy external calcareous shell
  3. C
    Metameric body segmentation, jointed chitinous appendages, and a hydrostatic skeleton
  4. D
    Secondary pentaradial body symmetry, a water vascular system, and tube feet for movement

Answer

Cephalopods are characterized by a closed circulatory system, a highly developed nervous system with complex image-forming eyes, and a foot modified into arms or tentacles.
Members of the class Cephalopoda differ from other molluscs by having a closed circulatory system with capillaries to deliver oxygen rapidly during active locomotion. They also possess large, image-forming eyes similar in efficiency to vertebrate eyes, and their muscular foot has evolved into tentacles surrounding the head for prey capture.

Step-by-Step Solution

1
Analyze the general characteristics of the phylum Mollusca.
Molluscs are typically unsegmented, soft-bodied organisms with a muscular foot, visceral mass, mantle, and usually an open circulatory system.
Establishing baseline molluscan features highlights the specialized evolutionary divergences in Cephalopoda.
2
Identify the unique adaptations of the class Cephalopoda.
Cephalopods (e.g., squids, octopuses) adapted to an active predatory lifestyle by developing a closed circulatory system with systemic and branchial hearts, advanced sensory organs including image-forming eyes, and tentacles derived from the foot.
High metabolic rates required for active swimming demand efficient closed blood circulation, unlike slow-moving gastropods or bivalves.
3
Match these adaptations with the correct response option.
The option specifying a closed circulatory system, image-forming eyes, and tentacles correctly describes Cephalopoda.
This option accurately captures both physiological and morphological specializations distinguishing cephalopods from other molluscan classes.

Key Concept

Cephalopod Physiological and Anatomical Adaptations
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Topics

Higher Invertebrates: Annelida, Mollusca, Arthropoda, and Echinodermata

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