It meant that the nervous system of the ctenophore had evolved from the ground up, using a different set of molecules and genes than any other animal known on Earth. It was a classic case of convergence: the lineage of ctenophores had evolved a nervous system using whatever genetic starting materials were available. In a sense, it was an alien nervous system – evolved separately from the rest of the animal kingdom.
But the surprises didn’t stop there. The ctenophore was turning out to be unique from other animals in far more than just its nervous system. The genes involved in development and function of its muscles were also entirely different. And the ctenophore lacked several classes of general body-patterning genes that were thought to be universal to all animals. These included so-called micro-RNA genes, which help to form specialised cell types in organs, and HOX genes, which divide bodies into separate parts, be it the segmented body of a worm or lobster, or the segmented spine and finger bones of a human. These gene classes were present in simpleton sponges and placozoa – yet absent in ctenophores.