An anonymous reader writes: When Leonid Moroz, a neuroscientist at the Whitney Laboratory for Marine Bioscience in St. Augustine, Fla., first began studying comb jellies, he was puzzled. He knew the primitive sea creatures had nerve cells — responsible, among other things, for orchestrating the darting of their tentacles and the beat of their iridescent cilia. But those neurons appeared to be invisible. The dyes that scientists typically use to stain and study those cells simply didn’t work. The comb jellies’ neural anatomy was like nothing else he had ever encountered.
After years of study, he thinks he knows why. According to traditional evolutionary biology, neurons evolved just once, hundreds of millions of years ago, likely after sea sponges branched off the evolutionary tree. But Moroz thinks it happened twice — once in ancestors of comb jellies, which split off at around the same time as sea sponges, and once in the animals that gave rise to jellyfish and all subsequent animals, including us. He cites as evidence the fact that comb jellies have a relatively alien neural system, employing different chemicals and architecture from our own. “When we look at the genome and other information, we see not only different grammar but a different alphabet,” Moroz said.