The Cloudy Periwinkle, Littoraria nebulosa (Lamarck, 1822), can be found along the coast of Southwest Florida living high above the high tide line on hard surfaces, mostly on dead tree trunks and branches. Periwinkles are marine gastropods that became almost completely independent of the aquatic environment. I took the photo on the right last weekend at Cayo Costa State Park during one of Captiva Cruises trips to the island. The image shows groups of unusually bluish-colored cloudy periwinkles thriving on trunks of dead black mangrove trees. The black mangrove trees were killed during Hurricane Charley in 2004.
The Cloudy Periwinkle, shell and (right) living snails at Cayo Costa State Park.