Southwest Florida Shells
by José H. Leal
Family Isognomonidae
Isognomon alatus
(Gmelin, 1791)
Flat Tree Oyster
Growing up to 95 mm (3.7 inches), individuals of this species rely on mangrove roots for substrate, forming aggregations attached to the roots via bundles of fibers called byssus. Not a true oyster, Isognomon alatus is a rare find along the coast of Southwest Florida, with very few examples from our immediate area present in the larger American museum collections. The species is common in the Tampa Bay area and along the east coast of Florida. There are a couple of holdings in our collection from Marco Island, but only recently we confirmed the presence of the species in Lee County. The main photo shows a juvenile of the species collected by Steve Rosenthal near the Goodland Bridge (Collier County) tentatively identified as this species. Lorin Buckner found and photographed a couple of Flat Tree Oysters near Sanibel (second photo). And Amy Tripp registered the presence of the species on her boat dock on south Marco Island (third photo).