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Difficulty: MediumLower Invertebrates: Porifera, Coelenterata, Platyhelminthes, and Nematoda

An animal specimen collected during a field study is triploblastic, unsegmented, possesses a pseudocoelom, and has a complete digestive tract with both a mouth and an anus. To which phylum does this organism belong?

  1. NematodaAnswer
  2. B
    Platyhelminthes
  3. C
    Coelenterata
  4. D
    Porifera

Answer

Nematoda
The correct answer identifies Nematoda because roundworms are characteristically triploblastic, unsegmented, possess a pseudocoelom derived from the blastocoel, and have a complete digestive tract featuring both a mouth and an anus.

Step-by-Step Solution

1
Analyze the structural characteristics described in the question stem.
The organism is triploblastic (three germ layers), unsegmented, has a pseudocoelom (false body cavity), and features a complete digestive system (mouth and anus).
Identifying diagnostic anatomical features allows precise classification into the correct lower invertebrate phylum.
2
Compare the features against the characteristics of lower invertebrate phyla.
Porifera lack true tissues. Coelenterata are diploblastic with an incomplete gut. Platyhelminthes are triploblastic but acoelomate with an incomplete gut. Nematoda possess three germ layers, a pseudocoelom, and a complete gut.
The presence of a pseudocoelom combined with a alimentary canal having separate oral and anal openings is unique to Nematoda among the listed lower invertebrate groups.

Key Concept

Body plan and structural characteristics distinguishing lower invertebrate phyla (Porifera, Coelenterata, Platyhelminthes, and Nematoda)
Estimated Time:1m 0s
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Topics

Lower Invertebrates: Porifera, Coelenterata, Platyhelminthes, and Nematoda