See text Isognomon is a genus of marine bivalve mollusks which is related to the pearl oysters.

However previous molecular phylogeny studies have shown that these tree oysters belong in the family Pteriidae.

[3] [4] These oysters grow to be about 4.75 inches (12.1 cm) in overall length, producing a highly irregular shell with a blue-gray and often heavily encrusted exterior but a smooth and pearly white interior.

They use their byssus to completely immobilize themselves to the roots of mangrove trees, corals, and other substrates.

[5] It is because of the preference for mangroves that these are sometimes called tree oysters[6] Extinct species within this genus include:[2]