Europe has a long history of human pressure on freshwater ecosystems. As pressure continues to grow and new threats emerge, there is an urgent need for conservation of freshwater biodiversity and its ecosystem services. However, whilst some taxonomic groups, mainly vertebrates, have received a disproportionate amount of attention and funds, other groups remain largely off the public and scientific radar. Freshwater mussels (Bivalvia, Unionida) are an alarming example of this conservation bias and here we point out six conceptual areas that need immediate and long‐term attention: knowledge, threats, socioeconomics, conservation, governance and education. The proposed roadmap aims to advance research, policy and education by identifying the most pressing priorities for the short‐ and long‐term conservation of freshwater mussels across Europe.

Mussels are intermediate hosts of digenean trematodes, but determinants of these infections remain unknown. To address this problem, we collected duck mussels Anodonta anatina in eighteen lakes from northeastern Poland and examined how mussel age, sex, and the encrustation with zebra mussels Dreissena polymorpha and environmental conditions in lakes influenced infection rates. We also assessed parasitic preferences to host gonads and hepatopancreas and the impact of parasites on female fertility. Mussels were infected with Rhipidocotyle campanula and Phyllodistomum sp. Infection rates were higher in older and female mussels but were unrelated to the biomass of encrusting D. polymorpha and the trophy, thermal conditions, and Ca²⁺ availability. Parasites occupied gonads more often than hepatopancreas. Infected females were less likely to carry glochidia and incubated fewer glochidia. We suggest that the risk of infection by digenean trematodes increases with the amount of water processed by filter-feeding hosts and/or that parasites actively seek hosts which can provide them with abundant resources. This mechanism explains why parasites more often occupied older and female mussels and targeted their gonads. Future research on trematode-mussel interactions should integrate knowledge on different elements of the complex trematode life cycles, including effects of higher-order hosts such as fish.

We studied shell variation in the thick-shelled river mussel (Unio crassus Philipson, 1788) sampled from two sites of very different character: (1) a rocky channel (San river) and (2) a fine-sediment channel (Zborowianka river). The analyzed mussels differed significantly between the sampled channels in almost all analyzed phenotypic traits and shape indices. Intersexual variation was so low that it cannot be used effectively for sexing in this species. The growth rate was much higher in the fine-sediment and nutrient-rich channel than in the rocky one, but the asymptotic shell length for the rocky channel was larger than for the fine-sediment channel, suggesting higher survival in the mountainous, unmodified river. Shell size differed significantly within the rocky channel, depending on microhabitat: shell size and dorsal arching were much greater in mussels living in the strong current of the rocky midchannel than in those inhabiting still water at the nearest bank. The results demonstrate that microhabitat conditions significantly determine shell shape.