The Genus Pinctada

The Genus Pinctada, Roding 1798
The family Pteriidae is composed of nine or ten genera, and pearl oysters belonging to the Pinctada and Pteria genera are the most important from our point of view. We start off with the firts of these genus.

Pinctada History and Discovery
  • Historically, there is a large amount of duplication among the names of pearl producing mollusks. This is partly due to independent geographical discoveries that were later found to be the same oyster. Furthermore, the crossover between a subspecies and a unique species is vaguely defined. Discoveries may originally be noted as a subspecies and then later revised to belong to a unique species and vice versa.
  • Due to these reasons, there are numerous synonyms for most of the pearl producing mollusks. Other names -older and not used today- for Pinctada are Avicula (aviculides), Meleagrina and Margaritifera . Although the name Pinctada first appeared in 1798 as part of J.F. Bolten's classification, it did not resurface until 1915, and was not widely accepted until the 1970's.
  • Margaritifera means, "bearer of pearls" and is derived from the Greek word for "pearl" (margarites) and the Latin word "to bear" (ferre).
  • Many of the origins for the names of pearl-producing oysters come from words pertaining to birds. For instance, the name Avicula originates from the Latin word "avis", meaning "bird". This term is credited to J.G. Bruguiere in 1792, though references to the term date back as early as 1705.
  • The first reference to the name Pinctada was made by Dezalier d'Argenville in 1792, and also includes an avian comparison. D'Argenville believed the grey color of the Pinctada shells were similar to a guinea fowl and named the genus after the French word "la pintade", which refers to the grey and white speckled feathers of a guinea fowl.

  • Pinctada shells serve as the main identifier of the Pteriidae family. Though it is their nacreous lining that distinguishes pearls of a particular species, the shells serve as a main tool for identification. The hinge that connects the two halves of a Pinctada shell can either have small ridges ("teeth") or none at all.
  • In 1901, English zoologist Jameson classified 34 species of Pinctada and divided them into two groups: those with teeth (such as the Akoya-gai and Mabe-gai pearl oysters) and those without (such as the Black and White/Golden lipped pearl oysters). Jameson's method was revised and clarified by G. Ranson in 1961. Ranson provided detailed descriptions and measurements of the shells that clarified what constituted "teeth" in a shell. He also included information on habitat, geographical distribution, and synonyms. Though there has been considerable disagreement on his nomenclature and classification, Ranson's work is the most comprehensive classification to date.
  • The number of Pinctada pearl oyster's species have been under scrutiny since 1994, when Shohei Shirahi published his comprehensive guide (Pearls and Pearl Oysters of the World) and reduced the number of species to about 9 species, and Southgate (The Pearl Oyster, 2008) mentions just 4 commercial species: maxima, margaritifera, imbricata and mazatlanica.

Pinctada Habitat & Ecology
Most Pinctada shells are found in the Caribean-Pacific and Indo-Pacific. They have never been reported on the west coast of Africa or around the islands of the eastern Atlantic. The two major pearl-mollusk regions are known as the Western (Caribean-Pacific) and Eastern (Indo-Pacific). In both regions, all precise locations for Pinctada have water temperatures that rarely fall below 20 degrees Celsius (68 degrees F) and are generally higher (up to 32 degrees Celsius or 89.6 degrees Fahrenheit).
Pinctada-shell-comparisson-Outer.jpg - Pinctada species shell comparison (exterior)
The size and growth rate of Pinctada corresponds directly to water temperature. In warmer tropical waters, shells are larger and grow faster. The size of a pearl is often an indication as to what region the pearl originated from (larger pearls usually originate from larger shells). Though there may be regional differences in a species' shell size and shape, the inner soft body that produces the pearl of a particular species is the same throughout. For this reason, a geographical discovery of a different looking shell sometimes leads to falsely creating a new subspecies when the inner soft body, and thereby the pearls, had previously been recorded.

Pinctada-Inner-shells.jpg - Inner shell comparison of Pinctada species

Pinctada oysters cluster in large, dense colonies. Sometimes they can be found in shallow water (less than 1 meter/3 feet) but thrive in 30-120 feet water. Although water temperature and food supply contribute to the ultimate depth, seabed conditions are the primary factor. Pinctada require a firm foundation for the mollusk to adhere to by means of organic threads called byssus.
Main hazards for Pinctada pearl oysters include pollution, natural predators, overcrowding and shifting currents and environmental change.

The Pearls of Pinctada
  • The genus includes most of the pearls that are found in fashion. From the exotic South Sea pearls (Pinctada maxima) to the classic Akoya pearls (Pinctada imbricata), shells from the genus Pinctada inspire the majority of pearls' fashion portfolio.
  • Many famous and historical pearls originated from the American "Panamic Black Lip Oyster" or Pinctada mazatlanica that was fished from Mexico's Gulf of California (Sea of Cortez), Panama and all the way down to Costa Rica. These pearls include "La Peregrina", "La Pellegrina", "The Big Lemmon" and many others.
  • Some shells of Pinctada maxima are so large that they are of "dinner plate" diameters and were historically critical to the mother-of-pearl industry. Also included within Pinctada are Tahitian pearls (Pinctada margaritifera) and tiny natural "Pipi pearls" found from the Indian Ocean to the Central Pacific (Pinctada maculata).

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