Pearl-Producing Mollusks (Molluscs)
Scientific Classification Of Pearl-Producing Mollusks
Mollusks encompass the second largest phylum of the animal kingdom (there are approximately 128,000 different species). The phylum is divided into two subphyla, only one of which contains species that produce pearls. Conchifera is the name given to the subphylum of mollusks that produces pearls. In this discussion, a pearl-producing mollusk is one that will produce jewelry-quality pearls.
Pearl-Producing Mollusks Are Not Oysters
Most pearl-producing mollusks are bivalves, meaning their shells have two halves connected by a hinge, like a clam. Although there are approximately 20,000 species of bivalve mollusks, only relatively few of these species are used in pearl culturing to create commercial pearls. The term “pearl oyster”, commonly used in the pearl trade, is in fact incorrect - pearl producing mollusks are not oysters. Though edible oysters can occasionally produce a pearl, they are of no commercial significance. Furthermore, for the safety of our teeth, pearls in edible oysters are undesirable. Commercial farming beds for oysters are in fact shut down if pearls persist to form within them.
The Anatomy Of Pearl-Producing Mollusks
The anatomy of a bivalve mollusk facilitates the production of pearls. Unlike a closed snail, or gastropod shell, a bivalve clamshell is open and water filled, leaving more room for pearls to form. Most bivalves are also passive filter feeders - meaning they maintain an open relationship with the environment by constantly circulating water in order to supply food. This process is critical for pearl production, since most natural pearls are formed as a reaction to a parasite or foreign object within the shell. The open relationship of the bivalve structure increases the probability of foreign objects and creatures to enter, and the possibility of a natural pearl to develop.
Gastropods Are A Different Pearl-Producing Mollusk
In contrast, gastropods do not rely on water flow for food and are usually predators who deliberately scrape food from rocks or from prey. Gastropods are also mobile and able to expel foreign particles before they become a pearl's nucleus through movement. Mobility has been a difficult factor in culturing abalone pearls. Abalone pearls come from large, ear-shaped snails, whose movement often expels inserted nuclei. Abalone pearls have beautiful blue-green nacre and display gorgeous rainbow iridescence. Because of their irregular shapes and liquid iridescence, abalone pearls epitomize the beautiful canvas of nacre that creates singular beauty in each pearl.