The four Mollusks

Mollusks represent the earliest forms of animal life and date back 550 million years. Pearl-producing mollusks first appeared 530 million years ago when mollusks developed shells. Pearls are organic gemstones which form inside a living pearl-producing mollusk.
A strand of pearls is one of the most elegant pieces of jewelry there is, yet these lustrous beauties have humble origins.

It has been estimated by scientists that only about a few dozen of mollusk species produce pearls and about half of them are used to produce cultured pearls.

There are two types of mollusks: saltwater and freshwater. Pearl-producing mollusks that live in salt water are often referred to as oysters. Pearl-producing mollusks that live in fresh water may be referred to as mussels.

When a natural irritant such as a fragment of shell, a scale or a parasite becomes lodged inside an oyster or mollusk, it gets coated with layer upon layer of nacre. As the layers of nacre build, the pearl grows. Depending on the type of mollusk, it can take from six months to seven years for the pearl to form.

There are four species of Mollusks that are primarily used to grow cultured pearls: akoya, Tahitian, South Sea, and freshwater.

South Sea oyster (Pinctada maxima)
South Sea cultured pearls are produced by the Pinctada maxima. The largest of all saltwater cultured pearl oysters, it can produce pearls from 8 to 20 mm in diameter, the average size is 13 mm. There are two types of Pinctada maxima oysters – silver-lipped (on the right) and gold-lipped (on the left). The silver-lipped type produces pearls that are mostly white to silver, sometimes with pink, blue or green overtones. The gold-lipped type produces mostly yellow to orangy yellow pearls, called “gold” and they are concidered to be the most valuable pearl type in the world.

The pearling regions of the South Seas stretch between the southern coast of Southeast Asia and the northern coast of Australia, and extend up to the Philippines. Australia is the largest producer of South Sea cultured pearls.

Black-Lipped South Sea Oyster (Pinctada margaritifera)

The saltwater Pinctada margaritifera or black-lipped oyster is from the Polynesian islands. These oysters produce the worlds second most valuable pearls "Tahitian Pearls" or "black pearls". Contrary to their name, Tahitian pearls are not actually cultured in Tahiti. These pearls are grown in the tropical lagoons and atolls located in the French Polynesian island chain by small family or community-owned farms. The harvests are sent to Tahiti for export.

The dark edge of the shell and its large size confirm that this is the shell of the Black-lipped Pearl Oyster. These oysters are the only ones that can produce pearls with a full color spectrum. Tahitian pearls are especially known for colors like dark grey, green, blue, purple and peacock. .

Akoya oyster (Pinctada fucata)
Akoya cultured pearls come from the saltwater Pinctada fucata oyster. The Akoya oyster is the smallest commercially farmed oyster that produces pearls.

Akoya cultured pearls are often perfectly round and have a high luster. Their color range varies from white to cream-colored and light pink. Akoya oysters are found on areas of the eastern coastline of North and South America, the east-coast of Africa, the Mediterranean and throughout the Indo-Pacific. Most notably, the Akoya oyster is found in Japan, where it has formed the basis of a multi-million dollar pearling industry.

Freshwater mussel (Hyriopsis cumingii)

The freshwater pearl mussel is an endangered mollusc species that is found mainly in clean, nutrient-poor, low-calcium rivers, ponds and lakes in China

Freshwater pearls used to be perceived as inferior compared to saltwater pearls, but today that has changed, and freshwater pearls have increased in quality and popularity. Freshwater pearls also have a very wide range of beautiful colors and different shapes.

Image sources: 1.8, 1.8.