Family Veneridae

Shell to 14 mm in length. Shell rounded-trigonal, shell surface smooth except for very low commarginal ridges. Inner edges of valves marked with microscopic oblique lines. Pallial sinus rounded, relatively short. Color white, often with brown or violet chevron-like markings, internally with infused with purple. Periostracum varnish-like, yellowish. Compare with locally occurring Transennella conradina, which is more pointed posteriorly and lacks the purple color. Also known as Stimpson's Transennella. This unusually dark shell was collected by Ken Piech on August 1, 2021, on Bunche Beach, Fort Myers, Florida. It is a new record of the species for the general area.

Shell size to 13 mm; shell trigonal, pointed posteriorly, relatively elongate for the genus. Shell surface smooth except for very fine growth lines. Inner edges of valves marked with microscopic oblique lines. Color white, often with sparse zigzag brown lines. Collected by Alice and Ken Piech on Sanibel.

Shell size to 20 mm; shell inflated, ovate. Sculpture of crowded growth lines. Umbones prominent, large. Lunule large, polished. Color white, sometimes with light-brown markings. Differs from Pitar fulminatus by smaller size, relatively higher shell, stronger hinge, and more subdued color pattern.

Shell size to 20 mm; shell inflated, ovate. Sculpture of crowded growth lines. Umbones prominent, large. Lunule large. Color white or chalk-white with light-brown spots of tent-like markings.

Shell size to 50 mm; shell elongate, cylindrical. Sculpture of radial ribs and well-spaced concentric lines; sculpture stronger on anterior part of shell; anterior ribs with scale-like projections. Color white. Lives in compacted mud bottoms. Formerly in separate family Petricolidae. The supplementary image of the live animal was taken by Amy Tripp on Kice Island, Collier County, in early 2015. The image shows the incurrent (bottom) and excurrent (top) siphons, and the clam's foot (lower left). The incurrent siphon directs seawater into the animal's mantle cavity (for oxygen uptake and filter-feeding), the excurrent siphon lets used water out.

Shell size to 65 mm; selatively heavy, trapezoidal, with truncated posterior margin. Sculpture of commarginal ridges bearing fine, evenly spaced radial lines that give ridges a crenulated aspect. Pallial sinus moderately deep. External color whitish, often mottled with light brown. This species is not commonly found in SW Florida. Single lot from Sanibel in BMSM collection dates from 1957.

Shell size to 3 mm; shell very small, trigonal, higher than wide. Surface polished, smooth. Umbones large, elevated. Color tan to brown. Do not confuse with Gemma gemma (Totten, 1834), which is not as high. Common on muddy sand bars. Pictures of Sanibel specimens by N. Barrera.

Shell to 120 mm, trigonal to rounded, with commarginal ("concentric") ridges on outer surface. It differs from its closest relative (and local native species), the Southern Quahog, Mercenaria campechiensis by smaller maximum size, violet-color tinges on the internal surface of its valves (lacking in the southern quahog), and lack of commarginal ridges on central part of the external shell surface. Given its commercial value, this is one of the best studied species of bivalves on the planet. The aquaculture industry has introduced the northern quahog to the bays and protected waters of Southwest Florida: the species was chosen over the native Mercenaria campechiensis because of the very short shelf life in this latter species. Both species can be found in the local areas invaded by M. mercenaria, and hybrids are not uncommon.

Shell size to 150 mm; shell thick, more inflated than in Mercenaria mercenaria, ovate-trigonal. Sculpture of irregular lines, more separated than in M. mercenaria. Lines never absent in middle of valve. Lunule as long as wide. Color dull-white to gray. Internally sometimes stained with purple. This species hybridizes with M. mercenaria in the southeastern United States. Juvenile shells (additional photo, size 30 mm) have purple zigzag lines; do not confuse these with Chione elevata or Chionopsis intapurpurea.

Shell size to 70 mm; shell ovate, much less elongate than Macrocallista nimbosa. Surface highly glossy. Sculpture of very fine growth lines under glossy layer. Umbones small. Lunule small. Color tan with irregular brown marks, sometimes arranged in radial bands. Internally white. Formerly known as Macrocallista maculata.