Amy Maxmen, reporting for Science News:
Comb jellies are gelatinous like jellyfish, but the similarity ends there. In body plan, jellyfish resemble the largely sessile, almost plantlike sea anemones, corals and other cnidarians: a group that dates back at least 550 million years. While jellyfish and other cnidarians have nerve cells that form a loose network in their bodies, comb jellies have a more sophisticated nervous system with a rudimentary brain and cellular connections called synapses that are also found in flies, humans and most other animals.
Yet, detailed looks at the genomes of two species of comb jellies suggest, surprisingly, that they are the more primitive animals, and not the jellyfish, sea anemones or corals, as has long been thought. It’s even possible that the sophisticated comb jelly lineage may have evolved before the brainless, gutless, muscle-less sea sponges.
These curious creatures, as Maxmen goes on to write, are upending many assumptions about how traits may evolve over time and then, perhaps counterintuitively, be lost.