Pearl oyster
Pearl oysters are marine mollusks belonging to the family Pteriidae, known primarily for their ability to produce pearls. They have a soft body encased within a two-part shell, known as valves, which are held together by a muscle. The shell is typically gray, with the upper valve being rounded and the lower valve flat. These oysters are hermaphroditic, meaning they can switch between male and female, producing millions of eggs during spawning seasons. When a small irritant, like a grain of sand, enters the oyster, it secretes nacre around the object, eventually forming a pearl.
Pearl oysters are predominantly found in saltwater environments, with the best-known sources for high-quality pearls located in regions such as the Persian Gulf, the Gulf of Mannar, and the South Pacific. Although natural pearls can occur, the majority of pearls on the market today are cultured, produced in farms where tiny pieces of mother-of-pearl are inserted into the oysters. The value of these pearls is influenced by various factors, including size, shape, and color, with hues ranging from white to black. Pearl oysters can live between 3 and 14 years, depending on their species, and include varieties such as the Akoya, black-lip, and gold-lip oysters.
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Subject Terms
Pearl oyster
This family contains oyster species from which people get pearls. Oysters form valuable pearls by secreting nacre around tiny objects that enter their shells.
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order: Pteriida
Family: Pteriidae
Genus: Various (see below)
Species: Various (see below)
Each pearl oyster has a soft body which lives inside a two-part shell. Each part of the shell is called a valve, and bi means two. An elastic muscle holds the two valves together, and in the center of the shell is a large muscle called an adductor muscle which tightens to close the valves.
Both valves of a pearl oyster's shell are fan-shaped or rounded, but they are not exactly the same shape, and the bottom valve is a little larger than the top valve. An oyster's shell is usually gray and rough. The upper valve is rounded in the middle and has rough edges, while the lower valve is flat with smooth edges. As an oyster's body grows, it secretes more shell material to make its shell larger. Lines across the two valves show an oyster's age. Pearl oysters are around a few inches (centimeters) across.
A pearl oyster's body rests inside a layer of skin that lines the smooth, white inside surfaces of the valves. This layer is called a mantle, and it is secreted by the oyster along with the shell. Tiny hairs called cilia line the mantle and wave back and forth to pull water into the shell. Gills then filter microscopic food particles like planktivores and zooplankton and absorb oxygen from the water. Two to three gallons (7 1/2 to 11 liters) may flow through the shell in one hour. Birds, snails, starfish, fish, octopuses, and skates all prey upon pearl oysters.
A pearl oyster switches between being male and female depending on the season, the water temperature, and the amount of salt in the water. Each oyster can be a male and produce sperm or a female and produce eggs. This is called being a hermaphrodite. Fertilization of eggs may occur in the water, or inside the females' shells. Each female may produce around 50 million eggs at one time. The larvae, or young, are called spat. The spat swim for several days and attach to an object to continue growing and developing shells.
A pearl oyster attaches itself with its fleshy foot to an object. Natural pearl oysters attach themselves in groups to rocks and other surfaces underwater.
A pearl forms inside an oyster when a grain of sand or some other small object gets trapped inside. This irritates the oyster, and it secretes nacre, or mother-of-pearl, to cover the object. With time, a round, smooth, shiny pearl forms.
Freshwater pearls form inside certain clams in temperate regions of the northern hemisphere. Most freshwater pearls come from Europe and China. Saltwater pearls, or Oriental pearls, are from saltwater oysters. The best saltwater pearls come from the Persian Gulf, but other good pearls come from the Gulf of Mannar between India and Sri Lanka, Celebes, Indonesia, islands in the South Pacific, the Gulf of California, the Gulf of Mexico, and the Pacific coast of Mexico.
Almost all the world's pearls are cultured pearls. This means people grow them inside oysters on farms. Tiny bits of mother-of-pearl are inserted into the oysters to be turned into pearls in 9 to 16 months. People have been doing this for hundreds of years. Most cultured pearls are from Japan and Australia. An oyster can produce three to four pearls in its lifetime.
The value of pearls depends on their size, shape, and color. Many pearls are white, but pearls may also be rose-colored, cream, gray, yellow, lavender, green, mauve, or black.
Pearl oysters have a lifespan between 3 and 14 years depending on the species.
Species include:
Akoya pearl oyster Pinctada fucata
Black-lip oyster Pinctada margaritifera
Gulf pearl oyster Pinctada radiata
Gold-lip oyster Pinctada maxima
Mazatlan pearl oyster Pinctada mazatlanica
Shark Bay pearl oyster Pinctada albina
White-lip oyster Pinctada maxima
Bibliography
Gamez, Albert. "Pinctada Margaritifera." Animal Diversity Web, animaldiversity.org/accounts/Pinctada‗margaritifera. Accessed 1 May 2024.
"Oyster." A-Z Animals, 24 Mar. 2023, a-z-animals.com/animals/oyster. Accessed 1 May 2024.
"Pearl Oyster." Department of Primary Industries and Regional Development, Government of Western Australia, www.fish.wa.gov.au/species/pearl-oyster/Pages/default.aspx. Accessed 1 May 2024.