Pinctada is commonly called pearl oysters and these are molluscs. These oysters have a strong inner shell layer composed of nacre, also known as "mother of pearl". Molluscs are terrestrial or aquatic (marine or freshwater) having an organ-system level of organization. They are bilaterally symmetrical, triploblastic and coelomate animals. The body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and visceral hump.