A New Study Finds that the Jelly, Not the Sponge, May Lie at the Base of the Animal Evolutionary Tree

I’m afraid, my dear friends, I will have to bow out of writing an extensive blog for this week. Not only are my knees figuratively giving way under the weight of two busy projects, but I’m in the thick of holiday festivity preparations (e.g., making that last-minute mad dash to stuff junk into closets, clear off tables, clean bed sheets, and put the last touches on the Christmas decor). However, I don’t wish to leave you with nothing, so here are a few crumbs of recent science news which, in my opinion, are pretty frigging cool.

For a wee background, I’ve had a general interest in sponges for a little while now because even though they don’t seem to have what we would classically call a “synapse”, they certainly have cells that contain what could be considered as precursors to synapses. They also don’t have neurons but do have the genes associated with such functions. So for us brainophiles, the sponge contains a lot of insight into how the central nervous system may have originally developed. And even more interesting, it had been thought that, due to their morphology and simplicity, they were probably the oldest of our animalian ancestors.

According to a study published this month in Science, however, it appears that sponges may not lie at the base of the animal family tree after all but that the comparatively more complex organisms, jellies, may be our oldest-known animalian grandfather. The group of scientists, headed by senior author Andreas Baxevanis and working at the National Human Genome Research Institute, is the first to have fully sequenced two separate genomes from the jelly known as the “sea walnut”. Unlike the sponge, these guys do have what we would call “neurons” and likewise have genes associated with these functions. This suggests that sponges at one point probably did have nervous systems but over time lost them. This also means that even the most basal of animalia had nervous systems.

So while I’m off to tally data and tidy the bed linens, please enjoy Science’s coverage on the paper, as well as the original paper itself. Ciao!

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The Ctenophore, “sea walnut”. Image borrowed from here.

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