Littorina saxatilis is a model organism to study speciation in natural conditions. The most recent research points towards genomic inversions playing an important role in this process. Currently, we are just completing a high-contiguity assembly using both Pacbio long read sequence data and Illumina short reads. We will then use this assembly in the analysis of both fine-scale (Koster region) and broad scale (North Atlantic) variation using WGS data (>400 individuals at 5-15x) This will help understand how the interplay between selective forces, neutral processes and chromosomal rearrangements could lead to speciation.