Moku o Loe, Kaneohe Bay, Oahu, 1 foot

Common in Kane'ohe Bay on seawalls and mangrove roots, these were introduced to Hawaii from Japan in 1926.  The shell is rectangular in outline and relatively smooth, with a pale internal scar, and attains 13 inches, 33 cm.  The North American Blue Point oyster, Crassostrea virginica, introduced in 1866, occurs in Pearl Harbor.  It has a tapering apex and scaly surface, and a dark internal scar.  It is illegal to harvest oysters in Hawaii, and ironically they are infected with larval tapeworms.