Freshwater Mussels Pacific Northwest - The Xerces Society

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2 beak of freshwater mussels in protection and restoration of our freshwater ecosystems. A more extensive bibliography, research highlights, and taxonomic updates also will make this new edition more relevant to resource managers and others interested in the science upon which this publication is based. Basic Anatomy Freshwater mussels are mollusks that produce a bivalved shell. The two valves are mirror images of each other and are connected by an elastic-like ligament along the dorsal hinge. The outside of each valve is covered with material called periostracum that gives the shell its color, and the inside of each valve is lined with a smooth mother-of-pearl material called nacre. The raised rounded area along the dorsal margin is called the beak; shells grow outward from the beak in a concentric pattern. Mussels may possess “teeth” on the hinge that create a strong and sturdy connection between the valves. There are two types of teeth—lateral teeth are thin elongate structures parallel to the hinge, and pseudocardinal teeth are short stout structures below and slightly in front of the beak. No native mussel species west of the Continental Divide have lateral teeth and only two species—Margaritifera falcata and Gonidea angulata—have pseudocardinal teeth (although the pseudocardinal teeth in illustration: Ethan Nedeau periostracum pseudocardinal teeth Freshwater Mussels of the Pacific Northwest shell ray growth line beak cavity Shell Morphology adductor muscle scars nacre hinge lateral tooth
foot illustration: Ethan Nedeau gill mantle water out water in Filter Feeding Mussels draw water and food into the inhalent aperture, use their gills to filter food and other materials from the water, and then expel filtered water and waste out the exhalent aperture. illustration: Ethan Nedeau Gonidea are very small). The species in the genus Anodonta have no teeth at all; the Latin word anodonta means “without teeth”. The living mussel occupies the cavity between the two valves. The only body parts that are visible outside of the shell are the foot that is used for locomotion and feeding, and the mantle edges that are modified into inhalent and exhalent apertures. The mantle is a thin sheet of tissue that lines the shell and envelops the body of the mussel. When disturbed, mussels will withdraw the mantle edges and foot into the shell and pull the two valves tightly together using their strong adductor muscles. This affords mussels some defense against predators and harsh environmental conditions. Mussels draw water and food into the body through the inhalent aperture and expel filtered water, waste, and larvae out the exhalent aperture. Typically, adult mussels in the West range in size from three to eight inches. Though sometimes mistaken for juvenile native mussels, fingernail clams and pea clams (Family Sphaeriidae), and non-native Asian clams (Corbicula fluminea) are much smaller than native mussels (less than one inch). Aside from obvious size differences, clams have thinner shells, different teeth morphology, mantles fused to form true siphons, and different reproductive strategies than mussels 61 . Life Cycle People who take the time to learn about freshwater mussels are amazed at the complex life cycle and reproductive traits that freshwater mussels possess. Freshwater mussels have separate sexes, although hermaphrodites (individuals with male and female traits that are capable of self-fertilization) have been documented for some North American species, including the western pearlshell 43,44 . During breeding, males release sperm into the water and females must filter it from the water for fertilization to occur. Fertilization occurs in a special portion of the female gill called the marsu- Freshwater Mussels of the Pacific Northwest 3
Page 1 and 2: Freshwater Mussels of the Pacific N
Page 3 and 4: Freshwater Mussels of the Pacific N
Page 5 and 6: CONTENTS Introduction to Freshwater
Page 7: Introduction to Freshwater Mussels
Page 11 and 12: Underwater view of western ridged m
Page 13 and 14: that live in flowing water may inha
Page 15 and 16: of glaciers, dispersal barriers, cl
Page 17 and 18: Freshwater mussels have been greatl
Page 19 and 20: Warning about collecting mussels! S
Page 21 and 22: Identification Field Guide The purp
Page 23 and 24: Anodonta Taxonomy It would be misle
Page 25 and 26: Anodonta General Account Variation
Page 27 and 28: Anodonta grow rapidly, often reachi
Page 29 and 30: Anodonta Clade 1 California Floater
Page 31 and 32: and east to western Wyoming, easter
Page 33 and 34: A. C. Internal and external valves
Page 35 and 36: The Yukon floater is found in lakes
Page 37 and 38: Small wooded creeks often have abun
Page 39 and 40: tion for this distribution is headw
Page 41 and 42: unknown. Native hosts with which mu
Page 43 and 44: A. B. C. Western Ridged Mussel A. E
Page 45 and 46: Conservation G. angulata have disap
Page 47 and 48: ies, especially in shallow water. A
Page 49 and 50: Literature Cited 1. Anthony, J.L.,
Page 51 and 52: 30. Frest, T. J. and E. J. Johannes
Page 53 and 54: 59. Mackie, G.L. 1991. Biology of t
Page 55 and 56: 90. Stagliano, D.M., G.M. Stephens,
Page 57: 118. Ziuganov, V., E.S. Miguel, R.J

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