"Common Slippersnail" or "Common Atlantic Slippersnail"
Crepidula fornicata (Linnaeus, 1758)
Family Calyptraeidae
The "Common Slippersnail" or "Common Atlantic Slippersnail" is easily found on S. Hutchinson Beaches They are arched with a inside deck or shelf where part of the snail resides. The shell length averages about an inch but large versions may reach almost 2".
The natural color is white or yellow/tan but shells have a variety of other colors (reds, dark yellows, black or gray) sometimes with stripe.
A grouop of Common Atlantic Slippersnails showinf some variation of color (S. Hutchinson Island 2020)
The inside look of the above shells showing the "shelf" or "deck"
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Bailey-Mitchell:
Family Calyptraeidae
Crepidula fornicata
(Linnaeus, 1758)
Common Atlantic Slipper Snail
Shell size to 40 mm; shell ovate, convex, with prominent apex which is turned to one side. Large, white internal septum with curved (convex) edge. Color cream to light-gray with longitudinal, fine dark-brown lines (illustrated) or interrupted dark-brown rays. This is one of the most common gastropod shells found on the beaches of Sanibel and Captiva. Slipper snails have shells that resemble limpets, but can be distinguished from these latter by the internal “deck” or “shelf” that houses the bulk of the snail’s organs, and the “twisted” shell apex. Unlike most gastropods, slipper snails are suspension feeders, scooping-up plankton and other materials in suspension from the water that flows through their gills. Common Atlantic slipper snails live on hard substrates such as large shells and rocks. They change sex, from male in the early part of their lives to female in the later stage, and form stacks, with larger individuals (the females) at the bottom, and smaller ones (the males) on top. The supplementary photo on the right shows a young (about 10 mm, or slightly less than ½ inch) common Atlantic slipper snail from Sanibel, showing, among other structures, the eyes, foot, propodium, and radula.