---

All those who think that bivalves are boring are in the best company. Karl von Frisch is reported to have turned the pages more quickly in texts where bivalves were treated because, according to him, they literally lack any behaviour. The fact that they can filtrate huge amounts of water, burrow into the sedi ment, actively swim, drill holes into rocks and boats or detect shadows with the aid of pretty blue eyes located on the rim of their mantle obviously left v. Frisch unimpressed. Why, then, a book on the large freshwater mussels (Naiads or Unionoida), which on first sight are much less spectacular than the marine ones? The main reason is that they are keepers of secrets which they reveal only on close and careful inspection. This is not only true for the pearls some species produce and which over centuries have contributed to the treasures of bishops and kings, but particularly for their ecology: their life cycles are linked with those of fishes, some can occur in incredible densities and some can live for more than 100 years. Thus, the presence or absence of naiads in a lake or stream has manifold implications.

---

I Systematics and Distribution.- 1 Characterization of the Unionoida (= Naiads).- 2 Freshwater Mussels (Hyriidae) of Australasia.- 3 Systematics and Distribution of the Recent Margaritiferidae.- 4 Population Genetics and Systematics of European Unionoidea.- II Life-History Strategies.- 5 Life-History Variation on Different Taxonomic Levels of Naiads.- 6 Larval Types and Early Postlarval Biology in Naiads (Unionoida).- 7 Plasticity of Life-History Traits in Unio crassus.- 8 Life-History Data on the Virtually Unknown Margaritifera auricularia.- III Populations and Communities.- 9 Factors Affecting Naiad Occurrence and Abundance.- 10 Effect of Muskrat Predation on Naiads.- 11 Glochidial Mortality in Freshwater Mussels.- 12 Macrohabitat Factors Influencing the Distribution of Naiads in the St. Croix River, Minnesota and Wisconsin, USA.- IV Evolutionary Biology.- 13 Framework and Driving Forces for the Evolution of Naiad Life Histories.- 14 A Phylogenetic Perspective on the Evolution of Morphological and Reproductive Characteristics in the Unionoida.- 15 The Evolution of the Unionacea in North America, and Its Implications for the Worldwide Fauna.- V Mussels and Environment.- 16 Environmental Relationships of Naiads: Threats, Impact on the Ecosystem, Indicator Function.- 17 Filtration and Respiration Rates of Two Unionid Species and Their Impact on the Water Quality of a Lowland River.- 18 Effects of Eutrophication on Unionids.- 19 The Extent of, and Causes for, the Decline of a Highly Threatened Naiad: Margaritifera margaritifera.- 20 The Pearl Mussel-Salmon Community in the Varzuga River, Northwest Russia: Problems of Environmental Impacts.- 21 How Environmental Information Can Be Obtained from Naiad Shells.- VI Synopsis.- 22 Ecology and Evolution of the Naiads.

---