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Order Description


Order Description

The Order Unionoida distinguishes freshwater mussels from other molluscs, such as scallops, clams, and oysters. All unionids pass through a larval phase as glochidia.

Family Unionidae

Most freshwater mussels in Georgia belong to the Family Unionidae. Freshwater mussels live under water, clinging to hard surfaces such as stones with their single foot. They eat by positioning themselves in the water current so that their siphon can pull the microorganisms the mussels eat from the current. Another siphon allows the mussel to excrete its waste into the current.

Freshwater mussels reproduce sexually, with the male releasing sperm into the water current and the female siphoning that sperm into her gills, where the unfertilized eggs are located. Once fertilization occurs, female freshwater mussels hold the fertilized eggs in their gills, where they develop into young mussels (called glochidiurn). At this stage, the glochidia (the plural of glochidium) are very small and have not developed their bivalve shell. The female mussel expels these glochidia into the current, where they attach themselves to the gills or fins of suitable host fish with small hooks. If it succeeds in doing this, the glochidium will live parasitically on the fish for some time until its organs are mature and the shell has started to form. At this stage, the glochidium releases itself from the host fish, falling to the riverbed where it will develop an adult shell and becomes a mature freshwater mussel.

Freshwater mussels can live a very long time, over 100 years in some cases, though very few survive that long. Many die before reaching maturity and those that survive to maturity are eaten by muskrats, raccoons, otters, turtles, birds, and people. Even more dangerous to freshwater mussels is the destruction of their natural habitats. Human activities, such as building dams and straightening river channels, upset the stream currents that the freshwater mussels depend on for food and reproduction. Siltation, toxic waste, and trash are additional perils. Finally, the disappearance of some species of fish from streams prevents some freshwater mussels from reproducing. This is because some species of freshwater mussels, while in their glochidium phase, are only able to cling to certain species of fish. So mussels are not only threatened directly by changes in freshwaters by also by changes that impact fishes.

Species in this family:
    Alabama Creekmussel (Strophitus connasaugaensis)
    Alabama Moccasinshell (Medionidus acutissimus)
    Alabama Spike (Elliptio arca)
    Altamaha Spinymussel (Elliptio spinosa)
    Apalachicola Floater (Anodonta heardi)
    Atlantic Pigtoe Mussel (Fusconaia masoni)
    Brook Floater (Alasmidonta varicose)
    Butterfly mussel (Ellipsaria lineolata)
    Chipola Slabshell (Elliptio chipolaensis)
    Coosa Moccasinshell (Medionidus parvulus)
    Delicate Spike (Elliptio arctata)
    Downy Rainbow (Villosa villosa)
    Fat Threeridge (Amblema neislerii)
    Fine-lined Pocketbook (Lampsilis altilis)
    Flat Floater (Anodonta suborbiculata)
    Florida Floater (Utterbackia peggyae)
    Gulf Moccasinshell (Medionidus penicillatus)
    Inflated Spike (Elliptio purpurella)
    Mountain Creekshell (Villosa vanuxemensis)
    Ochlockonee Moccasinshell (Medionidus simpsonianus)
    Oval Pigtoe (Pleurobema pyriforme)
    Ovate Clubshell (Pleurobema perovatum)
    Pod Lance (Elliptio folliculata)
    Purple Bankclimber (Elliptoideus sloatianus)
    Rayed Creekshell (Anodontoides radiatus)
    Roanoke Slabshell (Elliptio roanokensis)
    Sculptured Pigtoe (Quincuncina infucata)
    Shiny-rayed Pocketbook (Lampsilis subangulata)
    Southern Acornshell (Epioblasma othcaloogensis)
    Southern Clubshell (Pleurobema decisum)
    Southern Creekmussel (Strophitus subvexus)
    Southern Pigtoe (Pleurobema georgianum)
    Southern Pocketbook (Lampsilis ornata)
    Tennessee Heelsplitter (Lasmigona holstonia)
    Threehorn Wartyback (Obliquaria reflexa)
    Triangle Floater (Alasmidonta undulata)
    Triangular Kidneyshell (Ptychobranchus greenii)
    Upland Combshell (Epioblasma metastriata)
    Wavyrayed Lampmussel (Lampsilis fasciola)
    Yellow Lampmussel (Lampsilis cariosa)