|Pteriidae, the pearl (or winged) oysters, have shells with long flat hinge lines and wing-like extensions on both sides of the hinge. The exterior surface may be smooth or have a series of thin overlapping plates. The interior of the shell is nacreous (having an iridescent luster) which is a source of mother of pearl. Pteriids, especially those in the genus Pinctata, are important sources of natural and cultured saltwater pearls. However, the species found in Texas produce pearls that are generally too small to be of gem quality. Pteriids are not closely related to true oysters. They attach to hard substrates using byssal threads whereas the edible eastern oyster, Crassostrea virginica, "cements" itself to hard objects, as do other oysters. There are 2 species of pteriids found in Texas waters.