Neighbor joining (NJ) tree based on Maximum Composite Likelihood (MCL) distances showing the phylogenetic affinity of the Ostrea sp. specimens used for this study (Ostrea sp-IRTA - Ebro Delta) to Ostrea stentina. Numbers near nodes give bootstrap support (%). The inclusion in the different groups of dwarf oysters proposed by Hu et al. (2019) is indicated. Groups 1 and 2 are O. equestris and O. aupouria from close but divergent populations from the Americas and Asian Pacific, respectively. Group 3 is a new species Ostrea neostentina sp. nov. found in southeastern Spain (Mar Menor lagoon), eastern Tunisia, Hong Kong, and Japan, and group 4 is O. stentina occurring in northern (Avilés in the Atlantic Ocean) and northeastern Spain (Alfacs Bay in the Mediterranean Sea), Portugal, Morocco, and northern Tunisia.