The nervous system of comb jellies seems to have evolved separately from those of other animals, researchers led by the University of Florida's Andrea Kohn report in Nature this week.
Kohn and her colleagues sequenced the genome of the Pacific sea gooseberry (Pleurobrachia bachei) and generated its transcriptome and the transcriptome of 10 other comb jellies. From this, they found that comb jelly genomes differ from those of other animals in their neurogenic, immune, and developmental gene content, as in they lack many of those genes. The researchers also placed comb jellies as the earliest lineage in Metazoa.
The researchers also argue that, since the comb jelly is missing many of the usual pieces of the nervous system — the Pacific sea gooseberry uses one or two neurotransmitters rather than all 10 of the primary ones seen in other animals, Nature News notes — it may have evolved independently.
“Everyone thinks this kind of complexity cannot be done twice,” first author Leonid Moroz from UF tells Nature News. “But this organism suggests that it happens.”