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

An unidentified arthropod specimen has a body divided into two main tagmata (cephalothorax and abdomen), possesses four pairs of jointed walking legs, and completely lacks antennae. Which class of organisms does this specimen belong to?

  1. ArachnidaAnswer
  2. B
    Insecta
  3. C
    Crustacea
  4. D
    Chilopoda

Answer

Arachnida
Members of the class Arachnida are uniquely characterized within the phylum Arthropoda by having bodies divided into a fused cephalothorax (prosoma) and an abdomen (opisthosoma), four pairs of thoracic walking legs, and no antennae.

Step-by-Step Solution

1
Analyze the anatomical features described in the specimen stem
Body plan consists of two tagmata (cephalothorax and abdomen), 4 pairs of walking legs (8 legs total), and 0 antennae.
Diagnostic anatomical structures such as leg count, body segmentation, and antennae presence distinguish the main classes of Arthropoda.
2
Compare given features against diagnostic arthropod class criteria
Arachnids are defined by 4 leg pairs and 0 antennae. Insects have 3 leg pairs and 1 antenna pair. Crustaceans have 5+ leg pairs and 2 antenna pairs. Chilopods have 1 pair of legs per segment.
Matching structural characteristics identifies Arachnida as the correct class.

Key Concept

Diagnostic anatomical features of Arthropoda classes
Estimated Time:1m 0s
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Topics

Higher Invertebrates: Annelida, Mollusca, Arthropoda, and Echinodermata

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