Novos ramos surpreendentes na árvore da família dos artrópodes

Surprising New Branches on Arthropod Family Tree


ScienceDaily (Feb. 10, 2010) — Any way you look at it -- by sheer weight, species diversity or population -- the hard-shelled, joint-legged creepy crawlies called arthropods dominate planet Earth. Because of their success and importance, scientists have been trying for decades to out the family relationships that link lobsters to millipedes and cockroaches to tarantulas and find which might have come first.

Centipede. (Credit: iStockphoto)

In a scientific and technological tour de force that was nearly a decade in the making, a team of scientists from Duke University, the University of Maryland and the Natural History Museum of Los Angeles County have compared genetic sequences from 75 different species to draw a new family tree that includes every major arthropod lineage. Some of the relationships are so surprising that new names had to be coined for five newly-discovered groupings.

The work, which was supported by the National Science Foundation, appears online in the journal Nature.

A big surprise to tumble out of the new tree is that the closest living relatives of insects include a small and obscure group of creatures called remipedes that were only discovered in the late 1970s living in a watery cave in the Bahamas. With linear bodies like centipedes, simple legs and no eyes, it was thought that this small group -- now placed with cephalocarids in the newly-named Xenocarida or "strange shrimp" -- would be found at the base of the crustacean family tree.

Now, after analyzing 62 shared genetic sequences across all the arthropods, the researchers are putting the strange shrimp together with the six-legged insects, Hexapoda, to form a new group they dubbed Miracrustacea, or "surprising crustaceans." As a "sister clade" to hexapods, the Xenocarida likely represent the sort of creature that came onto land to start the spectacular flowering of the insect lineage, said Cliff Cunningham, a professor of biology at Duke who led the study.

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