Ctenophore (IMAGE) Vanderbilt University Medical Center Caption The comb jelly, or ctenophore, is an ancient marine invertebrate that may be the key to understanding the transition from single-celled to multicellular animals and the evolution of tissues, Vanderbilt University researchers reported this week. Credit Photo courtesy of Alexander Semenov. Usage Restrictions Photo courtesy of Alexander Semenov. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.