Population genetic structure and phylogeography of Mesokalliapseudes macsweenyi (Crustacea: Tanaidacea) in the northwestern Atlantic and Gulf of Mexico

► Significant genetic structure among Gulf of Mexico/Atlantic populations of M. macsweenyi. ► Genetic structure is consistent with expectations based on life history. ► Demographic analyses inferred population expansion in Gulf of Mexico. ► Four divergent Atlantic haplotypes might be representative of an undersampled lineage. ► It appears that multiple factors have influenced the evolutionary history of M. macsweenyi.