Stinging Cells (image) University of California - Davis Caption On the left is a hydra stained in blue where the light-sensitive opsin gene is expressed. On the right, two tentacle bulbs showing the arrangement of neurons and stinging cells (red), muscle fibers (green) and cell nuclei (blue). Credit David Plachetzki, UC Davis Usage Restrictions May be used with credit. 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.