Hydra Vulgaris Contracting (IMAGE) Marine Biological Laboratory Caption Hydra vulgaris in control media: Ectoderm muscle activity before contraction (left) and after contraction (right). Credit Wataru Yamamoto Usage Restrictions Please use with proper 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.