Family Calyptraeidae

Shell size to 13 mm; shell ovate, thin for genus, convex. Shelf margin extending further forward on left side; shelf margin often slightly arched. Color cream-white, with distinct chestnut-brown spots or streaks, sometimes brown overall with darker spots. Shelf whitish. Individuals in this species undergo a brief free-living larval stage (called pediveliger). The specimen on the right possibly a female, has a smaller individual attached to its shell, possibly a male.

Shell size to 38 mm; shell similar to Crepidula fornicata, but with internal septum straight, muscle scar under right edge of septum. Color white with small, well-defined brown spots. As most species in the family, C. maculosa broods the eggs in capsules stored between the head and the foot (photo). The egg capsules contain each between 10-20 eggs only (last photo), which develop into miniature adults inside the capsules, bypassing a free-swimming larval stage. The second image is a photo of female snail with eggs by Amy Tripp, February 2021. The third image is a close-up of an egg mass.

Shell size locally to 40 mm, species gets to 56 mm in parts of the Eastern Seaboard. 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.

Shell to 43 mm; shell flat or taking shape of substrate. Septum relatively small, less than half length of shell. Color pure white inside and out; outside surface sometimes with thin, tan periostracum. Although having a shell virtually indistinguishable from that of Crepidula atrasolea Collin, 2000, C. depressa has white foot and planktotrophic development, whereas C. atrasolea has a blackish foot and is a direct developer. (The illustrated specimens, lot BMSM 15001, were examined and cited in Collin, 2000.)

Shell size to 40 mm; flat or taking the shape of substrate. Septum relatively small, less than half length of shell. Color white inside and out; outside surface sometimes with thin, tan periostracum. Although having a shell virtually indistinguishable from that of Crepidula depressa Say, 1822, C. atrasolea has blackish foot and direct development, whereas C. depressa has a white foot and is a planktotrophic species. The two specimens illustrated on left, part of lot BMSM 15002, are also part of the original material examined by Collin, 2000.

Shell size to 12 mm; shell cap-shaped, conical, with circular base. Apex central. Shell "aperture" represented by a sinuous, flaring shelf inside shell. Edge of shelf near the center is thicker, round in cross-section, and corresponds to columella of regularly coiled gastropods. Color white.

Shell size to 26 mm, sculptured with rough, small spines arranged along ribs that radiate from apex. Apex turned to one side. Interior with white platelike septum. Color white, light-gray, brownish, or rarely greenish, sometimes with rays of lighter color.