The brown seaweed known as sea potato (not to be confused with the heart urchin also known as sea potato) is smooth, round and irregularly lobed. The ball feels like a mass of jelly. When young, sea potato is solid. However, as it ages, it grows and fills with gas. If it grows large enough, it can pull up the stone or shell it is attached to and move to other places by the current or wind. However, the species found in the Netherlands rarely grows large enough to accomplish this feat. Sea potatoes are found in the Oosterschelde, the Wadden Sea (recently found in the pleasure harbor on Texel) and particularly in the Grevelingen.