I noticed a snail this morning that has small thin piece of algea with fuzzy top growing on its shell. It's hard to tell from the picture, but the top half is green and the bottom is white. The tip also looks a little fuzzier in the picture than it does in person. It also seems fairly stiff. It barely moves even in the higher flow areas of my tank. I haven't noticed it growing anywhere else in the tank. Any idea what this could be?