Nerve Cells and Bacteria in Hydra (IMAGE) Kiel University Caption Body contractions in Hydra are triggered by nerve cells (in green), while bacteria (rod-shaped cells in red) influence the underlying pacemaker activity. Credit Image: Christoph Giez, Dr. Alexander Klimovich Usage Restrictions None 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.