Freshwater Mussels Pacific Northwest - State Water Resources ...

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KEY TERMSIt can be daunting to learn all of the words used to describe the shape andappearance of mussels. Species identification is a visual process, so we try tominimize the technical words and illustrate the ones that we use. Please alsorefer to the general morphology diagrams on pages two and three.Directions and Dimensionsdorsal(top)lengthwidthanterior(front)posterior(back)heightventral(bottom)Left versus right valve: Place theshell in your palm with the nacretoward you and the beak up. If thebeak is toward the right, it is the leftvalve. If the beak is toward the left,it is the right valve.beak toward rightleft valvebeak toward leftright valveShell ShapeL:H = ratio of length to heightelongate(L:H = or > 2.0)subtrapezoidal (L:H = or > 2.0)elliptical (L:H = 1.5 2.0)laterallycompressed(end view)laterallyinfl ated(end view)ovate (L:H = 1.5)16Freshwater Mussels of the Pacific Northwest
IDENTIFICATION KEYThis key was developed to enable the user to identify adult mussel shells orlive animals. Descriptions, photographs, and illustrations are provided in thespecies accounts. Species in the genus Anodonta are difficult to separate; seepage 19 for an explanation. This key can be used to make a best guess aboutspecies of Anodonta, but experts should confirm the identification.Key to GenusOutline of shell triangular or round. Beak inflated and centrally locatedalong dorsal edge. Well-developed concentric sculpture lines, absent onother genera (introduced)...Asian clam, Corbicula (page 41)Well-developed pseudocardinal teeth. Ventral margin slightly concave.Nacre purple on fresh specimens. Arborescent papillae surrounding theincurrent opening...western pearlshell, Margaritifera (page 34)Distinct heavy ridge running at an angle from beak to posterior ventralsurface. Shell thick, heavy, sturdy. Divided, purplish incurrent aperturepapillae...western ridged mussel, Gonidea (page 38)Pseudocardinal and lateral teeth and heavy ridge absent. Shell thin,light, and fragile. Single, whitish incurrent aperture papillae...Floaters,Anodonta (page 19)Key to Species1a. Outline of shell triangular or round. Well-developed concentricsculpture lines. Lateral teeth serrated. Adults are small (to about2.25 in, though rarely more than one inch)… Asian clam, Corbiculafluminea (page 41)1b. Outline of shell elongate or ovate. Adults larger than 2.25 in…22a. Shell thick, heavy, sturdy…32b. Shell thin, light, fragile. Hinge teeth absent…4 (genus Anodonta)3a. Pseudocardinal teeth greatly reduced or inconspicuous and lateralteeth absent. Distinct, heavy ridge running at an angle from beak toposterior ventral surface. Ventral margin of shell straight or broadlycurved…western ridged mussel, Gonidea angulata (page 38)Freshwater Mussels of the Pacific Northwest 17
Page 6 and 7: 4. SettlementJuvenile mussels relea
Page 8 and 9: Mussels can inhabit both pristine a
Page 10 and 11: Mussels as BiomonitorsFreshwater mu
Page 14 and 15: Healthy rivers and healthy salmon r
Page 16 and 17: Shoreline searches (top), clearbott
Page 20 and 21: 3b. Hinge with well developed pseud
Page 22 and 23: Anodonta DescriptionSize: Up to eig
Page 24 and 25: Anodonta and Gonidea situated in th
Page 26 and 27: The John Day River is home to the C
Page 28 and 29: Winged floaters inhabit sloughs of
Page 30 and 31: Oregon floaters can be found in Upp
Page 32 and 33: Kachess Lake in Washington is home
Page 34 and 35: The Yukon floater is found in lakes
Page 36 and 37: Small wooded creeks often have abun
Page 38 and 39: DistributionThe western pearlshell
Page 40 and 41: The Crooked River is home to popula
Page 42 and 43: DistributionWestern ridged mussels
Page 44 and 45: Zebra musselsphoto: U.S. Geological
Page 46 and 47: 44Freshwater Mussels of the Pacific

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