Living Nautilus
The 7.2 nautilus item; in 7.3, the tentacles are white and the shell is more orange.
Stack Size 1

Living nautilus is an item that you can get when you right click the nautilus mob. This effectively "catches" the nautilus. Right clicking a block or liquid with the living nautilus item will "release" it (note that it will suffocate on land). Living nautilus cannot be consumed, but can be cooked in a furnace to produce sio-chiu-le, a food item.