Convergent evolution isn’t a new thing, of course — the retina being the usual example. But neurons are a different story.
Emily Singer, for Quanta Magazine:
Moroz’s primary evidence for an independent origin of neurons in comb jellies comes from their unusual nervous systems. “The ctenophore’s nervous system is dramatically different from any other nervous system,” said Andrea Kohn, a molecular biologist who works with Moroz. Comb jellies appear to lack the commonly used chemical messengers that other animals have, such as serotonin, dopamine and acetylcholine. (They do use glutamate, a simple molecule that plays a major role in neuronal signaling in animals.) Instead, they have genes that are predicted to produce a slew of neural peptides, small proteins that can also act as chemical messengers. “No other animal except in this phylum has anything like that,” Kohn said.
But critics question this assertion as well. Perhaps comb jellies really do have the genes for serotonin and other neural signaling molecules, but those genes have evolved beyond recognition, Arendt said. “It could just mean [that comb jellies] are highly specialized,” he said.
They’re fascinating creatures, regardless of whether they’re merely exotic, or outright space aliens.