Measuring less than one inch in length I never would have seen these well camouflaged critters without the help of my dive master. They are also called Coleman Shrimp. See Fire Urchin Close and Large Fire Urchin. For the square version of this image go to Fire Urchin Shrimp (square).
This image is available in standard and square formats. The maximum sizes are 6 x 9 and 6 x 6 respectively.