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Oyster can reach 3 to 14 inches in length and 1.7 to 7 ounces of weight.
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Oyster has rough, extremely hard, oval or pear-shaped shell that protects soft, grey and slimy body hidden inside.
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Shell is made of calcium. Most oysters have whitish-grey shell that is white-colored from the inside.
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Oyster has three-chamber heart and colorless blood. It breathes via gills and excretes waste products via pair of kidneys. Oyster has very strong adductor muscle which keeps the shell closed.
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All oysters can be divided in four main groups: true oysters (that are part of human diet), pearl oysters (those that produce pearl), thorny oysters (those with thorny shells) and saddle oysters (those with very thin shells).
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Pearl oysters produce pearl around small grain of sand or some other irritant trapped in the shell. They repeatedly cover grain of sand with mixture of calcium and protein (substance called nacre) until prominent, white, yellow, rose or black-color pearl is created, usually 3 to 6 years later.
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Oyster is filter feeder. Water constantly circulates through the shell and brings nutrients (plankton) that end up trapped in the gills.
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Oysters are part of human diet for thousands of years. They can be consumed raw or cooked. Oysters have salty, pleasant taste and they represent good source of vitamins, minerals and proteins. They are often cultivated in the artificial ponds (oyster farms) to ensure constant supply and good quality of meat.
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Edible oysters can be harmful for the human health when they are harvested from the polluted areas (they easily accumulate toxins in the body).
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Natural enemies of oysters are various fish, marine mammals, birds and sea turtles.
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True oysters live in the colonies called oyster reefs or beds.
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Oysters reproduce during the warm period of year.
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Most species of oyster are hermaphrodites, while some species possess either male or female reproductive organs. Many oysters are able to change gender.
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Females produce up to million eggs per season and release them into the water. Only 6 hours after fertilization, free-swimming larvae emerge from the eggs. Free-swimming stage lasts 2 to 3 weeks. After that period, larvae transform into adults and attach themselves to the substrate where they will spend the rest of their life.
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Oyster has an average lifespan of 1 to 3 years.
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