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Cultivation of the Marine Pelagic Tunicate Dolioletta gegenbauri (Uljanin 1884) for Experimental Studies
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How did indirect development with planktotrophic larvae evolve?

Claus Nielsen1

  • 1Zoological Museum, The Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark. cnielsen@snm.ku.dk

The Biological Bulletin
|June 27, 2009
PubMed
Summary
This summary is machine-generated.

Marine invertebrate biphasic life cycles evolved through either intercalation or terminal addition. Theories suggesting non-feeding ancestors are rejected, favoring a rapid Ediacaran radiation driven by tubular gut evolution.

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Area of Science:

  • Evolutionary Biology
  • Marine Invertebrate Zoology
  • Developmental Biology

Background:

  • Biphasic life cycles, common in marine invertebrates, involve distinct larval and adult stages.
  • Two primary theoretical frameworks explain their evolution: intercalation and terminal addition.
  • Understanding these evolutionary pathways is crucial for deciphering invertebrate diversification.

Purpose of the Study:

  • To critically evaluate existing theories on the evolution of biphasic life cycles in marine invertebrates.
  • To challenge hypotheses that posit non-feeding ancestors.
  • To propose an alternative framework for early animal evolution.

Main Methods:

  • Comparative analysis of existing evolutionary theories.
  • Critique of hypotheses regarding ancestral states and larval evolution.
  • Reinterpretation of paleontological events like the "Cambrian explosion".

Main Results:

  • Theories proposing non-feeding ancestors, including planula and trochaea theories, are deemed untenable.
  • Intercalation and terminal addition theories present contrasting hypotheses for life cycle evolution.
  • The Ediacaran radiation of eubilaterians is suggested as a precursor to the "Cambrian explosion".

Conclusions:

  • The evolution of a tubular gut was a pivotal event enabling new body plans and diversification.
  • Feeding larval stages are likely derived, not ancestral, in major lineages.
  • A rapid Ediacaran radiation, not solely the Cambrian explosion, marks early bilaterian diversification.