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Alveolates are a group of organisms recognized by the presence of alveoli, which are cytoplasmic sacs located beneath the cell membrane. While their function remains uncertain, alveoli may help regulate water balance by controlling how much water enters and leaves the cell. In dinoflagellates, these structures may serve as armor plates. There are three major types of alveolates: ciliates, which move using cilia; dinoflagellates, which use flagella for movement; and apicomplexans, which are...
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Acoel development supports a simple planula-like urbilaterian.

Andreas Hejnol1, Mark Q Martindale

  • 1Kewalo Marine Laboratory, Pacific Bioscience Research Center, University of Hawaii, Honolulu, HI 96813, USA.

Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences
|January 15, 2008
PubMed
Summary
This summary is machine-generated.

The urbilaterian, ancestor to all bilaterians, was simpler than previously thought, resembling acoelomorph flatworms. Its genome contained genes later co-opted for complex development after its evolution.

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Area of Science:

  • Evolutionary developmental biology
  • Comparative genomics
  • Animal evolution

Background:

  • Molecular studies transformed understanding of development and evolution.
  • Historical biases in reconstructing organismal relationships are being overcome.
  • Accurate mapping of characters through evolutionary time is now possible.

Purpose of the Study:

  • To discuss the developmental and morphological features of the urbilaterian.
  • To propose that the urbilaterian was simpler than the protostome-deuterostome ancestor.
  • To identify developmental changes in gastrulation leading to the urbilaterian.

Main Methods:

  • Comparative analysis of gene deployment in acoels.
  • Reconstruction of ancestral developmental pathways.
  • Examination of gastrulation evolution.

Main Results:

  • The urbilaterian, resembling acoelomorphs, was morphologically simpler than the protostome-deuterostome ancestor.
  • Gene deployment in acoels differs from predictions for the urbilaterian.
  • Some genes were likely co-opted after the urbilaterian's evolution.

Conclusions:

  • The urbilaterian possessed a simple morphology despite a complex genome.
  • Developmental pathways evolved significantly after the urbilaterian.
  • Gastrulation changes were key to the evolution of the urbilaterian from cnidarian-like ancestors.