All have in common a larval stage that is temporarily parasitic on fish, nacreous shells, high in organic matter, that may crack upon drying out, and siphons too short to permit the animal to live deeply buried in sediment.

[4][5] Families, genera, and species in the order Unionida are found on six continents, where they are restricted exclusively to freshwater rivers, streams, creeks and some lakes.

[6] Unionida burrow into the substrate in clean, fast flowing freshwater rivers, streams and creeks, with their posterior margins exposed.

[7] These clams have, like all bivalve mollusks, a shell consisting of two parts that are hinged together, which can be closed to protect the animal's soft body within.

Fertilised eggs move from the gonads to the gills (marsupia) where they further ripen and metamorph into glochidia, the first larval stage.

[10] A cyst is quickly formed around the glochidia, and they stay on the fish for several weeks or months before they fall off as juvenile freshwater mussels which then bury themselves in the sediment.

[11] This unique life cycle allows Unionida freshwater mussels to move upstream with the fish host species.

[12][13] These bivalve mollusks were heavily exploited for freshwater pearls, and for their nacre which was used in the button manufacturing industry in the late 19th and early 20th centuries.

The effects of heavy fishing for freshwater mussels in North America in for use in manufacturing buttons put many of these species close to extinction.

The common names of the most prolific pearl-bearing species include: the butterfly, ebony, elephant ear, heelsplitter, mapleleaf, three-ridge pigtoe, pimple back, pistol grip, and washboard.

By 1993 in the United States 31 different states were still reporting production of freshwater pearls and export of freshwater mussel shells, including: Alabama, Arkansas, Georgia, Illinois, Indiana, Iowa, Kentucky, Louisiana, Minnesota, Missouri, Nebraska, North Dakota, Oklahoma, South Carolina, South Dakota, Tennessee, Texas, and Wisconsin.

"[17] Over the course of nearly 30 years, John Latendresse devoted his money, time and effort to research and develop the cultured freshwater pearl industry in the United States.

John Boepple immigrated to the United States in 1887 and found that there were vast beds of thick freshwater mussel shells in Muscatine, Iowa, which he determined were perfect for making "pearl buttons".

Since freshwater mussels were so common and the profit potential in making "pearl" buttons was so high, some of Boepple's staff who knew his techniques were "recruited" by other businessmen to start competing businesses.

[14][15][16] The need to "catch" freshwater mussels for the "pearl" button industry spurred the invention of tools to make the job easier than "pollywogging" with bare feet.

[14][15][16] By 1899, there were sixty button factories in the river states of Illinois, Iowa, Missouri, and Wisconsin, employing 1,917 people.

This new button industry quickly placed a huge ecological demand on the freshwater mussels of the Midwestern United States.