Rainbow Lip Pearl Oyster, Pteria sterna: The Rainbow Lip Pearl Oyster has a thin, brittle dark brown shell with a large ear and a wing-like extension. The interior of the shell has a blue tinge and the periostracum is shaggy.
They reach a maximum length of 10 cm (3.9 inches) and heights of 8.5 cm (3.3 inches) and are found in low intertidal and shallow subtidal muddy bays and mud-rock areas.
They are found throughout the Sea of Cortez and along the coast of the Mexican mainland south to Guatemala.
The Rainbow Lip Pearl Oyster is a member of the Pteridae Family, which are the Pearl Oysters. They attach themselves to hard surfaces with threads called a byssus, rather than cementing themselves to hard sufaces as true oysters do.
They require more “open water” oceanic conditions than the edible species. This species was first cultured for pearls in French Polynesia in the late 1800s and produced most of the black pearls seen in Western countries including many of the larger pearls worn during the European Renaissance that came from either Panama or Baja California. They were considered to be of significant socioeconomic importance for 400 years.
In 1909 the world’s only commercial pearl shell farm, owned by a French Doctor, located in La Paz, raised some 8 to 10 million pearl oysters and had 800 permanent workers. Due to overfishing, the species became endangered and its commercialization was banned by the Mexican Government in 1939. Pearl culturing has recently returned to the Sea of Cortez generating approximately 4,000 black pearls per year for market. An on-line video at Youtube.com provides an excellent overview of this farm. Due to the beauty and rarity these pearls are the most sought after pearl in the world.