Pearl oysters, a term encompassing various marine mollusk species, are famed producers of lustrous pearls. 

The process starts when an irritant enters its shell, such as an invading worm or a bead placed by a pearl farmer. They react by secreting nacre, a mix of amino acids and calcium carbonate, encapsulating the irritant to form a pearl.

Each type creates pearls of distinct sizes and colors, shaped by the size of the producing species and the naturally occurring nacre color. 

For example, the black-lip oyster is responsible for the striking obsidian allure of Tahitian pearls. Meanwhile, the Akoya oyster species exert their efforts to yield pearls with neutral colors and green or pink overtones.

These mollusks attach themselves to rocky or gravelly seabeds in both saltwater and freshwater habitats. They also reside in controlled settings like pearl farms.