The gelatinous comb jellies are members of the phylum Ctenophora, meaning “carried by combs.” These gelatinous animals are the biggest organisms that swim by moving cilia, hair-like structures lining the walls of their bodies. Though they aren’t true jellyfishes, the similarity is uncanny. Comb jellies are at least 95% water, have no complex nervous system and usually bear tentacles for ensnaring prey. But their 520-million-year old relatives were very different.
Fossilized imprints from the Cambrian period found in China show that these ancient comb jellies coupled the usual features of the group, like the characteristic cilia, with unique structures such as bony plates, rods for internal support and spikes for protection. These invertebrates actually had a skeleton.
Gelatinous soft bodies aren’t often preserved and fossils of extinct comb jellies have always been rare. Paleontologists long suspected that ctenophores from previous eras were just as boneless as their modern counterparts, but the Chinese findings show that’s not the case.