Wholesale Banded Tun shells for sale in bulk, Tonna sulcosa, a lightweight shell for large hermit crabs measuring between approximately 3 inches and 3-1/2 inch in size. Banded tun shells or tonna sulcosa shells are from the family Tonnidae and are thin, light weight and have a large mouth opening. They are almost exclusively tropical, prefer deeper water, and feed mainly on fish, sea urchins and crustaceans. These shells are used for large hermit crab homes, displaying airplants and in making candles and other seashell crafts