Nature Nugget – Freshwater Mussels

Freshwater mussels, a type of mollusk, are benthic (bottom-dwelling) animals. Nearly 300 species occur in the United States, mainly in the Mississippi River drainage. Seventy percent of the United States species are either extinct, endangered, or in need of special protection because of habitat loss and degradation. Most freshwater mussels live with 30–100 percent of their shells buried in sand and gravel on the bottom of rivers and streams. Only a few are adapted to the still, deep, and often muddy waters of lakes, ponds, and reservoirs. Freshwater mussels are long-lived, some acquiring ages of 60 years or more. Large species, like the washboard mussel, can weigh as much as 4 pounds and measure nearly 12 inches in length.

Being bivalves, mussels feed by taking water into their shells through a siphon valve, filtering out algae, plankton, bacteria, and organic particles with their gills. The filtered water, along with waste and rejected particles, leave the mussel through a second valve. Mussels have a large muscular foot which they use for burrowing and moving around. This foot also helps anchor them in strong currents. Their main protection against predators is their shell, which consists of two halves joined by a hinge. The shell consists of four layers of non-living material made primarily of calcium carbonate. The outside shell layer, called the periostracum, contains the color, pattern, and other markings that help distinguish one species from another. Unique names like “monkeyface,” “threehorn wartyback,” and “pink heelsplitter” refer to the wide range of shell size, color, pattern, shape, and texture found among mussel shells. The innermost shell layer that comes in contact with the soft body of the animal is called the nacre.

In Arkansas, where there are 70 different species, the mussel shell industry is fairly big business. Previous to the late 1940s and the invention of plastic, mussels were harvested for the button industry. Now they are collected to be shipped to Japan for the cultured pearl industry. There they are processed into mother-of-pearl nuclei, which are round seed pearls or pellets that are inserted into pearl oysters. The oysters respond to this irritating foreign object placed in their shell by coating it with its own mother-of-pearl secretion, thus producing a pearl. This process takes six months to three years, depending on the size and quality of pearl desired. Freshwater mussels occasionally produce pearls, but they are rarely of any value.

Mussels have an unusual reproductive process. At certain times of the year, males release sperm into the water, which are then siphoned in by the females to fertilize their eggs. The female’s gills are then used as a brood pouch for the young until they develop into larvae called glochidia. When the tiny glochidia, just microns in diameter, reach a certain stage, they are expelled into the water to become parasites on fish. This stage lasts one to six weeks, depending on species; then, the now juvenile mussels drop loose to the bottom of the water to begin life as a free-living mussel.

Just as the mussel shell pellet is transformed into a pearl by being placed in contact with the oyster, where it is covered with its mother-of-pearl secretions, so the person who comes in constant contact with Christ and His redeeming love is covered with His righteousness and transformed into a goodly pearl. “Christ, the heavenly merchantman seeking goodly pearls, saw in lost humanity the pearl of price. In man, defiled and ruined by sin, He saw the possibilities of redemption. . . . God looked upon humanity, not as vile and worthless; He looked upon it in Christ, saw it as it might become through redeeming love.” Christ’s Object Lessons, 118.

David Arbour writes from his home in DeQueen, Arkansas. He may be contacted by e-mail at: