The transcriptome assembly of the European freshwater mussel Unio elongatulus C. Pfeiffer, 1825

Freshwater mussels of the order Unionida are a global conservation concern. Species of this group are strictly freshwater, sessile, and slow-growing animals, extremely sensitive to environmental changes. Human-mediated changes in freshwater habitats are imposing enormous pressures on the survival of freshwater mussels. In Europe, while a few flagship species are being protected, other highly imperilled species receive much less attention. Some European species still lack an understanding of their biology, ecology, and evolution and proper conservation assessments. This knowledge is further aggravated by the lack of genomic resources available, which are key tools for conservation. Here we present the transcriptome assembly of <i>Unio elongatulus</i> C. Pfeiffer, 1825, one of the least studied European freshwater mussels. Using the individual sequencing outputs from eight functionally representative mussel tissues we provide an annotated panel of tissue-specific Relative Gene Expression profiles. These resources are key to studying this species' biological and ecological features, as well as to help understand its vulnerability to current and future threats.