Giant Tun ( Tonna galea )

/ / Marine Inverts

Description

Tonna galea is a large, globular shell that reaches 250mm high (1; 2); it has a small, acute spire and a broadly flared aperture (1), the aperture is without operculum, and large with undulating lips (2). The columella is coarsely thickened (1) and there are seven whorls separated by a deep suture; the surface alternates with wide and narrows ribs (2). The umbilicus is open, and the siphonal canal is short (2). The giant tun has a chestnut-yellow colouration; the periostracum is brown and membranous (2).

There are three species in the genus Tonna; T. galea, T. maculosa and T. pennata. All three species can be found within the Mediterranean.

Behaviour

The tun shell has a large foot, which will remain outside of the shell because it is unable to fully retract into its shell (2).

Habitat

T. galea is found in the infra and circalittoral zones, on mixed and hard substrates to depths 20m and deeper (1; 2).

Life Cycle

The tun shell is gonochoristic and fertilisation is internal; the spawn is laid into stiff ribbons and bound with sand and mucus (1).

Distribution

T. galea is a cosmopolitan species, found within the Mediterranean, Atlantic Ocean and Canary Islands (1; 2; 4).

Food

The tun shell are hunting carnivores (1); feeding on holothurians which they anaesthetise them using a salivary secretion from their long proboscis (2).

Conservation Status

Although Tonna galea is not listed under the IUCN Redlist (5), it is listed under Appendix II of the BERN Convention (6).

References

Description written by Ben Harvey (2009)

(1)   Hayward, P., Nelson-Smith, T. & Shields, C., 1996. Collins Pocket Guide – Sea Shore of Britain and Europe. London: Harper Collins Publisher Ltd.

(2)   Delamotte, M. & Vardala-Theodorou, E., 2001. Shells from the Greek Seas. Athens: Goulandris Natural History Museum.

(3)   ITIS, 2009. ITIS Standard Report Page: Tonna. [Online] Available at: http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=73143 [Accessed 25 August 2009].

(4)   Gofas, S. (2009). Tonna galea (Linnaeus, 1758). In: Bouchet, P.; Gofas, S.; Rosenberg, G. World Marine Mollusca database. Accessed through the World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=141687 on 2009-08-25

(5)   IUCN 2009. IUCN Red List of Threatened Species. Version 2009.1. <www.iucnredlist.org>. Downloaded on 25 August 2009.

(6)   Europe, C.o., 2002. Convention on the conservation of European wildlife and natural habitats: Bern Convention. [Online] Available at: http://conventions.coe.int/Treaty/FR/Treaties/Html/104-2.htm [Accessed 25 August 2009].