Invertebrates are one of the largest groups of creatures in the oceans. Defined simply as animals without backbones, these spineless wonders have evolved into a nearly infinite variety of shapes, sizes, and colors under the sea. Some have used calcium to create hard outer shells. Others are squishy, with the water supporting their soft forms. The images in this gallery have been hand-selected by Sea and Sky for their visual beauty and represent some of the most amazing images of marine invertebrates. Click on an image above to begin a slide show. Use the buttons under each image to navigate through the slide show. You can use the buttons on the left side of this page to select another image gallery and begin a new slide show.