This is the tale of two sister species: one gets all the glory, and the other goes "mossly" unnoticed. But these two species are actually very similar and easy to confuse. The Turkey Wing (Arca zebra) has a shell coloration that resembles the color pattern on the wings of a Wild Turkey (and the shell outline evokes the wing's shape). The Mossy Ark (Arca imbricata) lacks that strong color contrast and the well-defined pattern present on the Turkey Wing. This latter species shows a long projection of the hinge line (the very straight white line on "top" of the shell, see picture) that is lacking in the Mossy Ark. In addition, the sculpture in the Turkey Wing consists of thin and raised radial (departing from the beak) lines, whereas the Mossy Ark has flatter and broader ribs. There are yet other differences, but now you have some basic information to help confirm (or change) the identity of some the ark shells you found this past season!
Valves of the Turkey Wing, Arca zebra (left) and the Mossy Ark, Arca imbricata, both from Sanibel. Photos by José H. Leal.