The Florida Horse Conch, Triplofusus giganteus, is the second largest gastropod in the world and the largest in the Atlantic Ocean. Its shell can grow to over 60 cm (24 in) long. The animal is colored bright orange, and there is a large operculum closing the aperture (as seen in the photo). At University Beach it seldon grows larger than 20 cm (8 in), and most shells are inhabited by crabs. The shell in the photos has a white polychaete tube around it. Larger shells are often paler orange in color.

This species is known in older literature as Pleuroploca gigantea.

Learn more about this species at the Biodiversity of the Gulf of Mexico (BioGoMx) database at:
http://gulfbase.org/biogomx/biospecies.php?species=Spp-33-0943

Edit 2017: I added more photos of this specimen, and information about where the species is discussed in the Encyclopedia of Texas Seashells (p. 222) and Texas Seashells, a Field Guide (p. 98)