Glass sponges live on the bottom of the ocean, as deep as 2,000 meters (about 6,500 feet) or more. They have special structures to anchor them and keep themselves upright. Those that live on sand, for example, have long tufts of fibers sticking out of their bases. Glass sponges are adapted to really cold water and are most abundant in polar regions such as Antarctica. The only time they are found close to the sea surface is when surface waters are chilly, such as below ice or where deep waters are upwelling to the surface. They were found in a Mediterranean cave, for example, only meters from the surface, thanks to a trapped mass of cold water. Glass sponges tend to live in clusters and have formed a reef in British Columbia that towers nearly 20 feet above the seafloor.