Objective: Genetic characterization of T. decussatus in the Azores as a highly isolated, pure stock of the species (founder effects, genetic differentiation, conservation and exploitation issues); investigating relationships and possible genetic interaction between T. decussatus and T. philippinarum. Design: Temporal sampling of T. decussatus in Faja de Santo Cristo (island of Sao Jorge in the Azores); additional sampling of the species and of T. philippinarum along the European coasts. Methodology: Allozyme electrophoresis; in the future possibly random amplified polymorphic DNA, single strand conformation polymorphisms and microsatellites.