Unionid mussel.html



Unionidae
The shell of a Duck mussel, Anodonta anatina
Scientific classification
Kingdom: Animalia Phylum: Mollusca Class: Bivalvia Subclass: Paleoheterodonta Order: Unionoida Family: Unionidae
Genera
See text for genera and species.

Unionidae is a family of freshwater mussels, aquatic bivalve mollusks which are sometimes known as river mussels, naiads or simply as unionids.

The range of distribution for this family is world-wide. The family is at its most diverse in North America, with about 297 recognized taxa¹.

Freshwater mussels occupy a wide range of habitats, but most often occupy lotic waters.

Shell description

The shell of unionids is equivalve and nacreous and has a thick periostracum. The hinge usually has two cardinal teeth and two posterior lamellar teeth.

Life habits

Unionidae burrow into the substrate, with their posterior margins exposed. They pump water through the incurrent aperture, obtaining oxygen and food.

Unionidae are distinguished by a unique and complex life cycle. Most Unionids are of separate sex (although some species, such as Elliptio complanata, are known to be hermaphroditic). The sperm is ejected from the mantle cavity through the male’s excurrent aperture and taken into the female's mantle cavity through the incurrent aperture. Fertilized eggs move from the gonads to the gills (marsupia) where they further ripen and metamorph into glochidia, the first larval stage. Mature glochidia are released by the female and then attach to the gills, fins or skin of a host fish. 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 mussels which then bury themselves in the sediment.

Genera within the family Unionidae

• Genus Alasmidonta
• Genus Amblema
• Genus Anodonta
• Genus Cucumerunio Iredale, 1934
  • Cucumerunio websteri delli, McMichael & Hiscock, 1958
  • Cucumerunio websteri websteri, Simpson, 1902
• Genus Elliptio
• Genus Epioblasma
• Genus Hyridella Swainson, 1840
  • New Zealand freshwater mussel, Hyridella menziesi, Gray, 1843
• Genus Lampsilis
• Genus Lasmigona
• Genus Obliquaria
• Genus Pseudanodonta
  • Depressed river mussel, Pseudanodonta complanata
• Genus Pyganodon
• Genus Quincuncina
• Genus Sinanodonta
  • Sinanodonta woodiana
• Genus Strophitus
• Genus Truncilla
• Genus Unio
• Genus Utterbackia

References

• Powell A. W. B., New Zealand Mollusca, William Collins Publishers Ltd, Auckland, New Zealand 1979 ISBN 0-00-216906-1

External links

• Missouri State Unio Gallery
• Freshwater Mollusk Conservation Society
• Ohio State University: Division of Molluscs - Freshwater Mussel Collection - Unionidae

Wikimedia Commons has media related to: Unionidae