Family Arcidae

Shell size to 75 mm; shell elongate-rectangular, equivalve. Hinge long, straight. Sculpture reticulated with little beads forming on intersection of radial and concentric elements, 6-8 beaded radial ribs present posteriorly. Byssal gap very large. Periostracum dark-brown, heavy, shaggy. Color dirty- to dark-brown.

Shell size to about 25-30 Shell elongate oval to quadrangular; differs from local arcids by its thin shell, with an alternating pattern of thicker and thinner radial ribs, which are in turn crossed by concentric ridges. Living delicate arks have a hairy, rich periostracum that is more abundant toward the posterior (more pointed) shell end. Shell color white, with brown periostracum. The species is known locally on Sanibel/Captiva from a few single valves found recently (illustrations, December 2015, December 2016) by Susan J. Hewitt on Turner Beach (Captiva side of Blind Pass).

Shell size to 45 mm; shell compressed ("flat"), surface criss-cross, radial (starting at the beak) and commarginal ("parallel" to margin) cordlets forming bead-like bumps at their intersections. Shell internally brown, darker externally. Found under coral heads and rocks; common on ledges and reefs offshore in the Gulf; species not commonly found on Sanibel/Captiva area. The valve illustrated was found at low tide on Blind Pass (between Sanibel and Captiva islands) by Karla Mason on March 13, 2014. The 2013 beach renourishment deposited offshore material in the area. There is ongoing discussion on whether the name Barbatia domingensis (Lamarck, 1819) should be applied to this species.

Shell size to 80 mm; shell elongate-rectangular (twice as long as high), equivalve. Hinge long, straight. Sculpture of about 26, irregular radial ribs, and fine concentric threads that cross ribs and interspaces. Byssal gap present opposite to hinge, moderately large. Periostracum brown and dense on fresh shells, covering color pattern almost completely. Color creamy-white, streak with reddish- to dark-brown wavy bands. Attached by byssus onto hard substrates.

Shell size to 40 mm; shell oblong, inequivalve, with left valve larger, overlapping right valve. Hinge straight. Sculpture of 30-35 radial ribs. Smallest species in genus Anadara. Periostracum dark-brown. Color white. This species has been reported in an 2012 article published by Susan Hewitt in The Festivus as the most common shell found on Sanibel beaches.

Shell size to 100 mm; shell large, oblong, slightly inequivalve. Sculpture of 30-38 curved radial ribs which increase in width toward margin. Each rib with faintly incised, longitudinal groove. Periostracum dark-brown. Color white.