Triplofusus giganteus

Triplofusus giganteus, commonly known as the Florida horse conch, or the giant horse conch, is a species of extremely large predatory subtropical and tropical sea snail, a marine gastropod mollusc in the family Fasciolariidae, the spindle snails, tulip snails and their allies. On average, it weighs over 11 pounds.

Although known as a horse conch, this is not a true conch, as it is not in the family Strombidae.

With a shell length that can reach 60 cm, this species is the largest gastropod in United States waters, and one of the largest gastropods in the world.

Taxonomy
Triplofusus giganteus was named by Louis Charles Kiener in 1840, originally as Fasciolaria gigantea. The species was subsequently assigned to Pleuroploca. The genus name Triplofusus was proposed for it in 1953. T. giganteus has also been known by the name Fasciolaria papillosa, which was named by George Brettingham Sowerby I in 1825, but it is impossible to confirm what species this name originally applied to, due to the brevity of the original description and loss of the type specimen.

Distribution
This large sea snail is found along the Atlantic coast of the Americas from the U.S. state of North Carolina to the north, to Yucatán in the Gulf of Mexico to the south.

Anatomy
Triplofusus giganteus is the largest species of snail in North America. It has been hypothesized that female individuals reach larger sizes than males. The animal can retract the soft parts entirely into the shell and close it with the operculum. The soft parts are bright orange in color.

Shell
The largest known specimen of Triplofusus giganteus had a shell 604.8 mm long. However, populations have declined in size in recent years due to overharvesting; the largest individuals observed in various recent surveys have had shells ranging from 341 to 400 mm.

The outline of the shell is somewhat fusiform, with a long siphonal canal, and having up to 10 whorls. Its sculpture present several spiral cords and axial ribs, some of which can form knobs on the whorls' shoulders.

The shell color is bright orange in very young individuals. The shell often becomes greyish white to salmon-orange when adult, with a light tan or dark brown periostracum.

Habitat
This species dwells on sand, weed, and mud flats from the low intertidal to shallow subtidal zones, in 20 foot (6 m) deep water. They are found at depths ranging from 0 to 100 m.

Feeding habits
Triplofusus giganteus is a predator, with a diet that consists primarily of large gastropods, such as tulip shell (Fasciolaria tulipa), the lightning whelk (Sinistrofulgur perversum), and the queen conch (Lobatus gigas) as well as some Murex species. T. giganteus rarely eats bivalves, even when they are readily available, with the exception of pen shells in the genus Atrina, which can comprise 20% of its diet. It has been observed (in an aquarium setting) to eat small hermit crabs of the species Clibanarius vittatus. Cannibalism has been documented in captive T. giganteus, but only seems to occur in individuals that have been deprived of sufficient food.

Reproduction
Female T. giganteus probably attain reproductive maturity at an age of six or seven years and shell length of 200 to 250 mm. In a single spawning event, a female can lay up to 400 egg capsules, each of which can contain 70 offspring. However, spawning events are infrequent and individuals probably only live a few years after attaining reproductive maturity.

Predators
T. giganteus are commonly eaten by tiger sharks.

Parasites
Parasites of Triplofusus giganteus include trematode Lophotaspis vallei.

Modern times
The U.S. state of Florida declared it the state seashell in 1969. The shell is popular with shell collectors partly because of its great size.

Archaeological and anthropological uses
In classic Mayan art, the Horse Conch is shown being utilised in many ways including as paint and ink holders for elite scribes, and also as a bugle or trumpet.

In southern Florida, Native Americans, including the Calusa and Tequesta, used the horse conch to make several types of artifact. The whole shell, or more commonly only the columella, was attached to a wooden handle and used as a hammer or woodworking tool. The body whorl was used as a drinking cup. The columella was also used to make plummets or sinkers.

Conservation
Populations of T. giganteus are in decline, and because of the rarity of their spawning events they are vulnerable to population collapse.