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A hexamer origin of the echinoderms' five rays.

Marc H E de Lussanet1

  • 1Department of Psychology, Westf. Wilhelms-Universität Münster, Fliednerstraße 21, Münster, Germany. lussanet@uni-muenster.de

Evolution & Development
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PubMed
Summary
This summary is machine-generated.

Echinoderms

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Area of Science:

  • Developmental Biology
  • Evolutionary Biology
  • Zoology

Background:

  • Echinoderms exhibit complex development and unique adult body plans, posing challenges in evolutionary comparisons.
  • The prevalent pentamerous symmetry in adult echinoderms contrasts with larval bilateral symmetry.
  • Difficulties in homologizing structures across echinoderm clades hinder their classification within deuterostomes.

Purpose of the Study:

  • To propose a novel hypothesis for the origin of pentamerous symmetry in adult echinoderms.
  • To demonstrate that adult echinoderm body plans can be directly derived from larval bilateral symmetry.
  • To firmly rank echinoderms within the bilaterians, including their adult forms.

Main Methods:

  • Development of a theoretical model based on a missing ray in larval echinoderms (hexamerous structure).
  • Testing model predictions against metamorphosis processes and morphology of extant and fossil echinoderms.
  • Generalizing established planes (M-plane, Ubisch's, Lovén's, Carpenter's) for all echinoderms.

Main Results:

  • The proposed hexamerous to pentamerous transition model successfully explains adult echinoderm morphology.
  • Metamorphosis and fossil records support the hypothesis of derivation from larval bilateral symmetry.
  • The theory provides a unified framework for understanding echinoderm body planes and evolution.

Conclusions:

  • Adult echinoderms are derived from their bilaterally symmetric larvae, confirming their status as bilaterians.
  • The study resolves long-standing mysteries surrounding echinoderm body plan evolution and symmetry.
  • This work offers fundamental insights into the developmental basis and evolutionary trajectory of pentamerous symmetry.