Marine gastropods in Florida are harvested by the marine-life trade, tourists (for shells), and traditional commercial fisheries, but stocks are not formally assessed for most species. The main goal of this project was to estimate biological variables that may be used to evaluate the Species of Greatest Conservation Need status of the banded tulip Ctnctura tilium and six other large marine gastropod species that are commonly encountered in the targeted habitats. The principal target, C. tilium, was listed in the 2012 State Wildlife Action Plan. The densities and size structures of C. Hlium and six co-occurring species of large marine gastropods in Tampa Bay were examined to evaluate population dynamics, seasonal variation, and habitat preferences of these species. Long-term trends in the densities of large, predatory marine gastropods in 10 regions from 2009 to 2017 were included. In Tampa Bay, strong habitat preferences were observed for all species studied: C. tilium and Melongena corona were most likely to be observed on oyster reefs, and Fasciolaria lulipa was found only in seagrass, whereas Strombu.s alalus. Triplofusus gigantea, Sinistrofulgur sinislrum, and Fulguropsis spirilla were more common on soft sediments. Seasonal variations in densities were weak; seasonal differences in size structure were more pronounced. The smallest individuals of C. tilium appeared in spring and summer; F. spirata, S. alatus, and S. sinislrum reached a detectable size in fall. The smallest detectable M. corona appeared in winter. Regionally, there were more gastropods in southwestern bay grass beds (Tampa Bay, Sarasota Bay, and Pine Island Sound) than in coastal seagrass beds (Big Bend. Citrus, Hernando, Pasco, and coastal Pinellas) or northern bays (St. Joseph Bay and St. Andrew Bay), and each region had characteristic species. As a group, tulip snails exhibited modest local declines in densities at two sites, whereas the whelks and T. gigantea varied annually but did not exhibit consistent trends during 2009 to 2017. The present study establishes a baseline of abundance for seven species of common marine gastropods and recommends expanded monitoring in multiple habitats to improve future analyses of abundance trends. KEY WORDS: Florida, Gulf of Mexico, snails, density, growth, recruitment, gastropods, Cinclura