Comb jellies are these beautiful, otherworldly creatures that sparkle gently in the sea. And now, if a study in the journal Science and another one in the journal Nature hold up, they may not be so gentle on evolution or the tree of life. These “aliens of the sea” are fundamentally changing how we think about both.
The standard line for evolution has been that all the complicated stuff evolved once. Way back when some common ancestor evolved a nervous system, muscles and so on and all of our systems are built on those first ones.
Seems reasonable given how hard it probably was to cobble together all the components to get these systems to work. And there was a lot of evidence to support this idea too. For example, it looked like a subset of parts of the nervous system were shared by all the animals that have a nervous system.
This no longer seems to be the case. Back in December, a group of researchers took a close look at the DNA of the sea walnut (Mnemiopsis leidyi) and found that it lacked the usual set of genes animals have to make a nervous system. They also found that this comb jelly lacked almost all of the genes needed to make muscles. This was even though this comb jelly has both muscles and a nervous system.
This result has now been confirmed in a study out on May 21 on a second comb jelly, the Pacific sea gooseberry (Pleurobrachia bachei). The researchers not only found that this comb jelly lacks the same set of genes, but they also showed that its nervous system works in a unique way too.