The Giant Tun, Tonna galea (Linnaeus, 1758) is a large gastropod, with a shell that may reach in excess of 150 mm (6 inches). The shell globose, with a short spire, and ornamented with around 20 spiral, strong but flat ridges. A thin shell allows ridges to show on its internal surface. The Giant Tun has a broad distribution in tropical and subtropical areas of the world’s ocean. The species includes a long-lasting, free-living (planktonic) larval stage that allows dispersal via currents over large oceanic expanses. Giant Tuns feed on Sea Cucumbers, Sea Stars, and Sea Urchins, using a feeding apparatus that includes a pair of jaws and acidic saliva containing sulfuric acid.
Although pieces of shells sometimes wash ashore on Sanibel, this illustration represents the first local record of a whole shell, found in December 2009 by Rob Meyer in shallow water at the eastern end of the island (young Oysters were living inside the shell when Mr. Meyer first found it). Photos by José H. Leal.