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Difficulty: MediumSupport Structures and Locomotion

An adult invertebrate specimen collected from soil leaf litter is observed to have a body divided into two distinct regions (cephalothorax and abdomen), four pairs of jointed walking appendages, and no antennae. Which taxonomic class and skeleton type correctly characterize this organism's support and locomotory framework?

  1. A
    Insecta, supported by a chitinous exoskeleton
  2. Arachnida, supported by a chitinous exoskeletonAnswer
  3. C
    Crustacea, supported by a hydrostatic skeleton
  4. D
    Myriapoda, supported by a cartilaginous endoskeleton

Answer

The specimen belongs to the class Arachnida and is supported by a chitinous exoskeleton.
Members of the class Arachnida (Phylum Arthropoda) have their bodies divided into two main parts: an anterior cephalothorax (prosoma) and a posterior abdomen (opisthosoma). They bear four pairs of jointed walking legs and lack antennae. Like all arthropods, their body is enclosed in a tough chitinous exoskeleton that provides rigid mechanical support, prevents desiccation, and serves as an attachment site for muscles that drive locomotion.

Step-by-Step Solution

1
Analyze anatomical features given in the scenario
Two body divisions (cephalothorax and abdomen), 4 pairs (8 total) of jointed legs, and 0 antennae.
These morphological features define the diagnostic characteristics of arthropod classes.
2
Identify the taxonomic class matching these appendages and body tagmata
Arachnida (e.g., spiders, scorpions, ticks, and mites).
Insects have 3 body divisions and 3 pairs of legs; crustaceans have 2 pairs of antennae and 5+ leg pairs; myriapods have many legs and 1 pair of antennae.
3
Determine the support structure characteristic of this phylum
Chitinous exoskeleton.
All arthropods possess an exoskeleton made primarily of chitin that serves as a protective framework and site for antagonistic muscle attachment during movement.

Key Concept

Arthropod Appendage Differentiation and Exoskeletal Support
Estimated Time:1m 0s
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Topics

Support Structures and Locomotion

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