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Comb Jelly Squeezes Out Sponge As First Animal
Sponges are getting squeezed out of a distinctive role in evolution with a new study saying they do not represent the oldest branch of the animal family tree after all.
The DNA research instead awards top spot to comb jellies, a group of gelatinous marine animals better known as the sea walnut, the sea gooseberry or the Venus girdle, according to the journal Science.
Scientists at the University of Miami say the Mnemiopsis leidyi may be "the earliest branch of the animal tree and the sister lineage to that of all other animals".
While life evolved from a single ancestor, scientists are always looking to find out more about how it happened.
More than half a billion years ago, long before humans appeared, the first split in the tree of life separated one lineage from all other animals and, traditionally, scientists have thought it was sponges.
The evidence in favour of comb jellies comes from deciphering the first complete genetic code from a member of this group with scientists being able finally to compare the full DNA codes from all the earliest branches.
Sorting out the early branching of the tree could help scientists learn what the ancestor of all animals was like.
But despite decades of study and the traditional view favouring sponges, there is plenty of disagreement about which early branch came first.
The question is "devilishly difficult" to answer, and the new paper is probably not the last word, said scientist Antonis Rokas of Vanderbilt University, who was not involved in the new work.
"The results need to be taken seriously," he said, but "I'm pretty sure there will be other studies that suggest something else".
The comb jelly is native to the waters of the western Atlantic.
It is blind, has no brain and is a carnivore. On the plus side, it does not sting.
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