The Crown Pearl V2: an improved genome assembly of the European freshwater pearl mussel Margaritifera margaritifera (Linnaeus, 1758)

Contiguous assemblies are fundamental to decipher the exact composition of extant genomes. In molluscs, this task is considerably challenging owing to their large size, heterozygosity, and widespread content of repetitive content. Consequently, the usage of long-read sequencing technologies is fundamental to achieve high contiguity and quality. The first genome assembly of Margaritifera margaritifera (Linnaeus, 1758) (Mollusca: Bivalvia: Unionida), a culturally relevant, widespread, and highly threatened species of freshwater mussels, has been produced recently. However, the current genome is highly fragmented since the assembly relied solely on short-read approaches. To overcome this caveat, here, a new improved reference genome assembly is produced using a combination of PacBio CLR long reads and Illumina paired-end short reads. This novel genome assembly is 2.4 Gb long, organized into 1,700 scaffolds with a contig N50 length of 3.4Mbp. The ab initio gene prediction resulted in a total of 48,314 protein-coding genes. This new assembly represents a substantial improvement and is an essential resource for studying this species unique biological and evolutionary features that ultimately will help to promote its conservation.