This sponge formed quietly over time in my son's 29g tank. While rearranging the rockwork, I discovered it and turned it toward the front to observe it. I'm not sure if it will continue to thrive now that it has been moved, but it is pretty cool looking. I named this 2" x 2" patch Structured Sponge for lack of a better name. Something to keep in mind when you remove or add rock to your own tank is to make sure the rock stays submerged at all times. When sponges are exposed to air, in general they die and can cause a real problem as they will rot in your tank. Inspect your rock carefully, and if you do some rearranging, put the rock in a container of saltwater to limit exposure to air. This sponge is usually Reef-safe.