''Tonna pennata'' is a large species of

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

, a marine

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

in the family Tonnidae, the tun shells. Commonly known as the Atlantic partridge tun, the species is a predator of animals much larger than itself, particularly

sea cucumber Sea cucumbers are echinoderms from the class Holothuroidea (). They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothuria ...

Description

This shell varies in colour from beige to dark brown, and the whitish markings are quite variable, which may account for the large number of

synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

s that exist. The shell is pear-shaped, with a moderately blunt apex; the wide, flared aperture with a thin lip occupies about three quarters of the length of the shell. The umbilicus is open and the columella twisted. The surface of the shell is finely striated, with shallow grooves between the ribs. The largest

whorl A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral ...

has about twenty ribs, and there is no operculum. The maximum shell length is about . In living animals, the

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

is white with brown markings, and flares widely as the animal moves about. The snail could be confused with ''

Tonna galea ''Tonna galea'', commonly known as the giant tun, is a species of marine gastropod mollusc in the family Tonnidae (also known as the tun shells). This very large sea snail or tun snail is found in the Atlantic Ocean, North Atlantic Ocean as far ...

'', but that species is more globular with a blunter apex; another similar species is ''

Eudolium bairdii ''Eudolium bairdii'' is a species of large sea snail, a marine gastropod mollusk in the family Tonnidae, the tun shells. Distribution This marine species has a circumtropical distribution in the Atlantic, Indian, and Pacific Oceans. Description ...

'', but that is usually found at much greater depths. '' Tonna perdix'' is a similar species from the Pacific Ocean, and the two may be part of a species complex.

Distribution and habitat

''Tonna pennata'' is found in shallow water in the tropical western Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico and in the eastern Atlantic in the

Canary Islands The Canary Islands (; es, Canarias, ), also known informally as the Canaries, are a Spanish autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to the African mainland, they are west of Morocc ...

Madeira ) , anthem = ( en, "Anthem of the Autonomous Region of Madeira") , song_type = Regional anthem , image_map=EU-Portugal_with_Madeira_circled.svg , map_alt=Location of Madeira , map_caption=Location of Madeira , subdivision_type=Sovereign st ...

and the West African coast. It is usually found in reef areas, on coral and rock, and in sandy areas and

seagrass meadow A seagrass meadow or seagrass bed is an underwater ecosystem formed by seagrasses. Seagrasses are marine (saltwater) plants found in shallow coastal waters and in the brackish waters of estuaries. Seagrasses are flowering plants with stems and ...

s. The minimum recorded depth for this species is 0 m; the maximum recorded depth is 13 m.

Ecology

''Tonna pennata'' is a predator, specialising in

s, particularly those in the family Stichopodidae. It also preys on bivalve molluscs and fish. It has a long eversible proboscis, with which it envelops smaller prey, or presses the organ against larger prey, secreting saliva containing

sulphuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

which paralyses its victim and starts the digestive processes. It attacks prey much larger than itself, such as the slow-moving sea cucumber ''

Isostichopus badionotus ''Isostichopus badionotus'', also known as the chocolate chip cucumber or the cookie dough sea cucumber, is a species of sea cucumber in the family Stichopodidae. This common species is found in warm parts of the Atlantic Ocean. Description Th ...

'', which can grow to a length of . The sea cucumber has developed a strategy for getting rid of its attacker. It stiffens the area round the injury which then softens, and muscular contractions cause a patch of integument to autotomise (come away from its body).

References

* 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 {{Taxonbar, from=Q3174983 Tonnidae Molluscs of the Atlantic Ocean Gastropods described in 1853 Taxa named by Otto Andreas Lowson Mörch