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Evolution is not a one-way road towards complexity

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Posted October 21, 2013

There are still a lot of unanswered questions about mollusks, e.g. snails, slugs and mussels. The research group of Andreas Wanninger, Head of the Department of Integrative Zoology of the University of Vienna, took a detailed look at the development of cryptic worms. The larvae of the wirenia argentea hold a much more complex muscular architecture than their adults—they remodel during their metamorphosis. That’s a clue that the ancestors had a highly complex muscular bodyplan. Their findings are published in the current issue of the scientific journalCurrent Biology.

 
Evolution is not a one-way road towards complexity
This is an image of Collected specimens of the neomeniomorph Helluoherpia aegiri(Aplacophora, Mollusca) from Bergen, Norway. Credit: Copyright: Maik Scherholz
 

With over 200.000 species described, the Mollusca—soft-bodies animals that, among others, include snails, slugs, mussels, and cephalopods—constitutes one of the most species-rich animal phyla. What makes them particularly interesting for evolutionary studies, however, is not the sheer number of their representatives, but rather their vast variety of body morphologies they exhibit. Ever since they have been unambiguously assigned to the phylum, a group of worm-like, shell-less mollusks whose body is entirely covered by spicules—the Aplacophora (“non-shell-bearers”, usually small animals in the mm-range that inhabit the seafloors from a few meters to abyssal depths) has been hotly debated as being the group of today’s living mollusks that most closely resembles the last common ancestor to all mollusks.

Read more at: Phys.org

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