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Comb jellies are our oldest cousins, not sponges

Comb jellies, a group of gelatinous marine animals, represent the oldest branch of the animal family tree.
More than half a billion years ago the first split in the family tree separated one lineage from all other animals. Traditionally, scientists have thought it was sponges but DNA research shows it was comb jellies
Whole-genome sequencing data shows that comb jellies branched from the rest of the animals before the sponge, a simple animal without complex cell types, according to a new study.

With our whole-genome sequencing data in hand, it is now clear that the cell types that make up muscles and nervous systems were either lost in some animal lineages or that, despite the complexity of these cells, they very well may have evolved multiple times.

—Joseph Ryan, Ph.D., lead author

The phylogenetic relationship of ctenophores (comb jellies) to other animals has been a source of long-standing debate.

Until recently, it was thought that Porifera (sponges) was the earliest diverging animal lineage, but recent reports have instead suggested Ctenophora as the earliest diverging animal lineage.

For the past 30 years, researchers have used whole-genome sequencing of organisms to advance their understanding of evolution.

The evidence in favor of comb jellies comes from deciphering the first complete genetic code from a member of this group. Scientists were finally able to compare the full DNA codes from all the earliest branches.

The analyses suggest that ctenophores are the sister group to the rest of the extant animals.

The results present a newly supported view of early animal evolution that accounts for major losses and/or gains of sophisticated cell types, including nerve and muscle cells.


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