The thin shell is ventricose, inflated, generally globular, rarely oblong, and encircled with ribs. The spire is short. The outer lip is crenulated and sometimes denticulated throughout its whole length. The oblong aperture is very large and emarginated inferiorly. The columella is channeled. There is no operculum.
The animal is very large, so as scarcely to be contained within its shell. The head is broad and swollen anteriorly, supporting two long, slender, obtuse, distant tentacles, dilated towards the base, where the eyes are situated. The mouth is large, muscular, strong, and retractile. The respiratory tube is pretty stout. Its cavity is large, entirely open, provided with two branchiae placed on the left side, the larger of which forms a large semicircle. The trunk is cylindrical, very much developed, flexible, capable of being turned in every direction at the will of the animal, and of elongating itself in a remarkable manner. It is furnished internally with several rows of hooks. The foot is ovate, large, and fleshy, bordering all parts of the shell. It is rounded, widened, lobed, and dilated anteriorly, with a horizontal furrow. The posterior extremity has no trace of an operculum. The reproductive organ of the male is very retractile.[2]
Anterior view of a live Tonna galea held in a human hand
The genus Tonna comprehends a small number of species, some of which attain so remarkable a growth that they are sometimes as large as a man's head. The general appearance of the shell, of an inflated, thick-set form, calls up the image of a tun, whence is derived its generic name. Thus, the characters which make up these species are a form more or less inflated, girdled, and very globular. The spire is much shorter than the body whorl. This causes the size of the aperture, which almost always occupies two-thirds of the length of the shell.[2]
The animals of the tuns are in general strongly colored, and painted with different tints which form bands and spottings upon their entire exterior.[2]
Rovereto, G. 1899. Prime ricerche sinonimiche sui generi dei gasteropodi. Atti della Società Ligustica de Scienze Naturali e Geografiche 10: 101-110
Iredale, T. & McMichael, D.F. 1962. A reference list of the marine Mollusca of New South Wales. Memoirs of the Australian Museum 11: 1-109
Vaught, K.C. (1989). A classification of the living Mollusca. American Malacologists: Melbourne, FL (USA). ISBN0-915826-22-4. XII, 195 pp
Wilson, B. 1993. Australian Marine Shells. Prosobranch Gastropods. Kallaroo, Western Australia : Odyssey Publishing Vol. 1 408 pp.
Gofas, S.; Le Renard, J.; Bouchet, P. (2001). Mollusca, in: Costello, M.J. et al. (Ed.) (2001). European register of marine species: a check-list of the marine species in Europe and a bibliography of guides to their identification. Collection Patrimoines Naturels, 50: pp. 180–213
Rolán E., 2005. Malacological Fauna From The Cape Verde Archipelago. Part 1, Polyplacophora and Gastropoda
Beu, A. G. (2005) Neogene fossil tonnoidean gastropods of Indonesia. Scripta Geologica 130, p. 1-186, pp. 166, figs. 327
Vos, C. (2007). A conchological Iconography (No. 13) - The family Tonnidae. 123 pp., 30 numb. plus 41 (1 col.) un-numb. text-figs, 33 maps., 63 col. pls, Conchbooks, Germany
Beu, A.G., Bouchet, P. & Tröndlé, J. 2012. Tonnoidean gastropods of French Polynesia. Molluscan Research 32(2): 61-120
Vos, C. (2012) Overview of the Tonnidae (MOLLUSCA: GASTROPODA) in Chinese waters. Shell Discoveries 1(1); pp. 12–22; Pls. 1-9
Vos, C. (2013) Overview of the Tonnidae (Mollusca: Gastropoda) in Chinese waters. Gloria Maris 52(1-2); pp. 22–53; Pls. 1-9
