Comb jellies, or ctenophora, are marine animals with gelatinous bodies. When they slowly move through the water, the scattering of light at the oscillating cilia causes a colourful rainbow effect, and they look like alien creatures in a foreign gallaxy.
Comb jellies live in tropical as well as in arctic waters, from the depth of the oceans to the surface, forming about 150 species. They are common, however, most people have never seen them. Although their bodies are transparent, comb jellies do not belong in the same phylum as jellyfish (cnidaria). Neither are they related to salps, another translucent ocean creature.
Ctenophores have muscle tissue, and nervous and digestive systems – but no nettle cells. They have extensive regenerative abilities to restore damaged tissue making them interesting for medical research. The complex animals can actively swim using cilia arranged in rows along their bodies. They are predators, eating other comb jellies, small crustaceans, and larvae of clams and snails. Comb jellies themselves are eaten by jellyfish and sea turtles. The bioluminescence of their bodies may act as a deterrent to potential predators.
You might thus think that ctenophores are evolutionarily younger than sponges (porifera) which just sit at the bottom of the sea and do not have nervous, digestive, or circulatory systems. But actually, comb jellies might have evolved before sponges since animals appeared some 500 to 600 million years ago. Which phylum first branched off from the animal phylogenetic tree remains a contested issue.