[Campbell Biology P.736] The text explains that Acoela was once classified under Platyhelmin... | Practice Question

The text explains that Acoela was once classified under Platyhelminthes but molecular analyses led to its reclassification as a separate lineage. Considering the described characteristics of both phyla, which statement best explains the rationale behind this reclassification?

  • A: Both Acoela and Platyhelminthes are described as having a saclike gut, implying their reclassification is solely based on genetic data.
  • B: Acoela possesses a simple nervous system, whereas Platyhelminthes are characterized by a central nervous system and bilateral symmetry, reflecting significant evolutionary divergence.
  • C: Platyhelminthes, including tapeworms, planarians, and flukes, have specialized organs for circulation, which Acoela lacks.
  • D: Acoela is significantly smaller than any organism classified under Platyhelminthes, leading to its reclassification.

Explanation

The text indicates that Acoela, despite superficial similarities to flatworms, is a 'separate lineage that diverged before the three main bilaterian clades'. This deep evolutionary divergence is supported by structural differences mentioned, such as Acoela having a 'simple nervous system' compared to the 'central nervous system' of Platyhelminthes. This fundamental difference in nervous system organization, coupled with molecular data, supports their reclassification as distinct phyla.