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Question

Difficulty: HardGrowth, Development, and Metamorphosis

During an ecological survey of a grassland habitat, a student collected an immature arthropod featuring three distinct body regions (head, thorax, and abdomen) and three pairs of jointed walking legs attached strictly to the thoracic segment. Microscopic examination revealed external wing pads on the immature stages, which reached maturity through a succession of nymphal instars without passing through a quiescent pupal stage. Which of the following correctly classifies the organism and its mode of development?

  1. An insect undergoing incomplete (hemimetabolous) metamorphosisAnswer
  2. B
    An arachnid undergoing incomplete (hemimetabolous) metamorphosis
  3. C
    An insect undergoing complete (holometabolous) metamorphosis
  4. D
    A crustacean undergoing complete (holometabolous) metamorphosis

Answer

An insect undergoing incomplete (hemimetabolous) metamorphosis
The correct answer identifies the organism as an insect undergoing incomplete metamorphosis because it possesses the diagnostic anatomical features of Class Insecta (three body regions and three pairs of thoracic legs) and exhibits hemimetabolous development characterized by progressive nymphal stages, external wing buds, and the absence of a pupal stage.

Step-by-Step Solution

1
Analyze anatomical features to identify the arthropod class.
The presence of three distinct body divisions (head, thorax, abdomen) and three pairs of legs attached to the thorax places the organism in Class Insecta (insects).
Arachnids have two body regions and four pairs of legs, while crustaceans typically have a cephalothorax and five or more pairs of legs.
2
Examine the developmental pattern to determine the type of metamorphosis.
Development involving nymphal instars with external wing pads and lacking a pupal stage indicates incomplete (hemimetabolous) metamorphosis.
Complete (holometabolous) metamorphosis requires a distinct larval stage, internal wing disc development, and a non-feeding pupal stage.

Key Concept

Insect Metamorphosis and Arthropod Classification
Estimated Time:1m 30s
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Topics

Growth, Development, and Metamorphosis

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