The windowpane oyster (Placuna placenta) is a bivalve marine mollusk in the family of Placunidae.[1] It is edible, but valued more for its shell (and its rather small pearls). The oyster's shells have been used for thousands of years as a glass substitute because of their durability and translucence. More recently, they have been used in the manufacture of decorative items such as chandeliers and lampshades; in this use, the shell is known as the capiz shell (kapis).[2] Capiz shells are also used as raw materials for glue, chalk and varnish.
Distribution extends from the shallows of the Gulf of Aden to around the Philippines, where it is abundant in the eponymous province of Capiz. The mollusks are found in muddy or sandy shores, in bays, coves and lagoons to a depth of about 100m (300feet).
Populations have been in decline because of destructive methods of fishing and gathering such as trawling, dredging, blast fishing and surface-supplied diving. In the Philippines, fisheries are now regulated through permits, quotas, size limits and protected habitats. In spite of this, resources continue to be depleted.[3]
The nearly flat shells of the capiz can grow to over 150mm in diameter, reaching maturity between 70mm100mm. The shell is secured by a V-shaped ligament. Males and females are distinguished by the color of the gonads. Fertilization is external and larvae are free-swimming like plankton for 14 days or attached to surfaces via byssal thread during metamorphosis, eventually settling on the bottom.[4] They consume plankton filtered from the water passing through their slightly opened shell; the oyster's shell closes when the bivalve is above water during low tide.
Aside from being abundant in the province of Capiz, capiz shells are also abundant in the island of Samal in the Philippines, where 500 tons of capiz shells are harvested every other year.
The capiz shells found around the island are harvested and transformed into various decorative products. As late as 2005, the residents of the island were trained to sustain the industry. However, the transfer of institutional knowledge to new generations to maintain the industry is in danger of being lost.[5]