Unionidae

mollusk family

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July 14, 2026

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The Unionidae family comprises freshwater mussels, also known as naiads. These bivalve mollusks are found worldwide, with a significant number of species in North America and Southeast Asia. Freshwater mussels typically have pear-shaped shells with a thick outer layer and a pearly interior. Their larvae, called glochidia, are parasitic, attaching to fish gills or fins for a period before developing into adult mussels.123

While many species are threatened by habitat degradation and invasive species like the zebra mussel, some North American unionids have historically been used for button making due to their nacreous shells.21

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conservation
Freshwater mussels and clams
…of the bivalve mollusk families Unionidae and Margaritiferidae. Of these, 21 have become extinct in the past century, and 70 percent are in danger of extinction. During this same period, engineers have extensively dammed and channeled North America’s rivers. The Tennessee River, for example, is dammed along its entire length…
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…of the bivalve mollusk families Unionidae and Margaritiferidae. Of these, 21 have become extinct in the past century, and 70 percent are in danger of extinction. During this same period, engineers have extensively dammed and channeled North America’s rivers. The Tennessee River, for example, is dammed along its entire length…
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bivalve
Distribution and abundance
…and two important families, the Unionidae and Corbiculidae, are predominantly freshwater with complicated reproductive cycles. There are no terrestrial bivalves, although some high-intertidal and freshwater species can withstand drought conditions.
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…and two important families, the Unionidae and Corbiculidae, are predominantly freshwater with complicated reproductive cycles. There are no terrestrial bivalves, although some high-intertidal and freshwater species can withstand drought conditions.
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bivalve
Reproduction and life cycles
In the freshwater Unionidae the released larva, called a glochidium, often has sharp spines projecting inward from each valve. The larva attaches to either the gills or fins of passing fish and becomes a temporary parasite. Eventually, it leaves the fish, falls to the lake floor, and metamorphoses…
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In the freshwater Unionidae the released larva, called a glochidium, often has sharp spines projecting inward from each valve. The larva attaches to either the gills or fins of passing fish and becomes a temporary parasite. Eventually, it leaves the fish, falls to the lake floor, and metamorphoses…
Read More