Ostrica europea Ostrea - Ostrea edulis

Ostrea (common name oyster) is a genus of bivalve mollusks with a rounded shell covered with wavy scaly gills. Ostrea edulis, Linnaeus, 1758, known by the common name of oyster, or flat oyster, or also as the European flat oyster, is a species of bivalve mollusk in the family Ostreidae.

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The two valves are unequal, and the lower one, to which the animal is anchored, is larger and more concave than the upper one. The mollusk has a rounded body, with fringed edges on the two mantle flaps. It lives in all European seas at shallow depths, clinging to rocks or other solid bodies. Some oysters, mainly species from eastern seas, produce pearls.

Description

Roundish, irregular shell with a rough surface, covered with wavy lamellae. It has an inequivalve shape. The right valve is flat and scaly, while the left valve, with which the mollusk attaches to the rock, is concave. It measures 7-12 centimeters in diameter or more.

The species should not be confused with Crassostrea gigas, the cupped oyster, which, as its common name suggests, has concave and elongated valves. This species, native to the Pacific, has in recent years[which?] supplanted the production of Ostrea edulis and has become the most widely available species on the market, as it is farmed in much of France. Crassostrea gigas alone accounts for 75% of European production.

Biology

They are proterandrous hermaphrodites. They usually change sex twice a year. The eggs are kept in the female’s palpebral cavity, where fertilization occurs. The zygotes and larvae are retained for 8–10 days inside the palpebral cavity, after which they are released into the water column at the veliger stage. Ostrea edulis veligers undergo a pelagic phase of 8–10 days before attaching to a substrate.

Distribution and habitat

The oyster lives attached to coastal rocks, from a few meters to about 50 meters deep, from which it is detached throughout the year, especially in spring and summer. The oyster is common but in sharp decline in the Mediterranean Sea, Atlantic Ocean, and North Sea.

It is farmed (oyster farming) in specific locations, such as Taranto, in Lake Fusaro, in La Spezia, in Rovinj and in France, along the coast of Normandy and Brittany and in Corsica, in the Diana pond.