These are single polyps of green mushroom, Discosoma cargreni from Florida. These are primarily a shallow water corallimorph (mushroom) that adapt really well to most aquariums. This color morph is mostly a light green with a pink mouth, and each polyp is about 1′ to 1.5″ in diameter.
Mushrooms are a lot like ricordea as far as care and feeding. They are mostly photosynthetic, but regular feeding will stimulate them to grow bigger and reproduce in your tank. You will not likely see them actively feeding, but they seem to somehow feed on the organics in the water and in the “dust” that settles on them, so when you feed them, dust them with a fine particle food.
Unlike ricordeas, discosoma mushrooms primarily reproduce by budding instead of division, so instead of waiting for them to form another mouth and split in half, watch for tiny daughter colonies sprouting up around the base of the parent colony.
We only sell single polyps and they usually don’t have much if any substrate on them. They seem to attach to most clean substrates within a week, so you shouldn’t have to do too much fussing with adhesives. Try placing them is a still part of your tank and allow them to attach to the rock or your choice or to bits of rubble on the bottom. Once they have attached to something, you can move them to other parts of the tank and they will usually stay there. Although they come from shallow, brightly lit areas, they will also thrive in shady areas of the tank.