News of the WeekEvolution

From a Flatworm, New Clues on Animal Origins

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Science  19 Mar 1999:
Vol. 283, Issue 5409, pp. 1823-1825
DOI: 10.1126/science.283.5409.1823

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As reported on page 1919, tiny marine worms called acoels may be one of the closest living representatives of the first bilaterally symmetrical organisms on Earth. Using DNA analyses, a research team concludes not only that the acoels don't belong with other flatworms, but that they alone represent a living relic of the transition between radially symmetrical animals such as jellyfish and more complex bilateral organisms such as vertebrates and arthropods. If this position in the evolutionary tree is confirmed, the acoels could provide a living window on early metazoan life.