Jellyfish in tank (IMAGE) Howard Hughes Medical Institute Caption Cassiopea jellyfish can swim, but prefer to remain stationary on the sea (or tank) floor, with their bells on the ground, and their tentacles floating above them. Credit Caltech Usage Restrictions Use with credit. 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.