A chromosome-level genome assembly of the common eider, <i>Somateria mollissima</i> (Linnaeus, 1758)

The common eider, Somateria mollissima mollissima (Chordata; Aves; Anseriformes; Anatidae), is a large sea duck with a circumpolar distribution. We here describe a chromosome-level genome assembly from an individual female. The haplotype-resolved assembly contains one pseudo-haplotype spanning 1,205 megabases (with both Z and W sex chromosomes) and one pseudo-haplotype spanning 1,080 megabases. Most of these two assemblies (91.13% and 93.18%, respectively) are scaffolded into 32 autosomal chromosomal pseudomolecules plus Z and W for pseudo-haplotype one. The BUSCO completeness scores are 94.0% and 89.9%, respectively, and gene annotations of the assemblies identified 17,479 and 16,315 protein coding genes. Annotation of repetitive sequences classify 17.84% and 14.62% of pseudo-haplotype one and two, respectively, as repeats. The genome of the common eider will be a useful resource for the widely distributed northern species in light of climate change and anthropogenic threats.