The attributes and traits of populations of intertidal invertebrates can become modified in response of the environmental pressures. Therefore, comparative studies of biological traits of range-edge populations versus non range-edge ones may provide essential insights into what processes determine their geographical distribution. In recent decades, the range of Siphonaria pectinata has expanded northwards on the Atlantic coast of the Iberian Peninsula, overlapped in time with significant changes in the sea surface temperature owing to weaker upwelling events. The main objective of this study was to explore differences in the traits and attributes between non range-edge and range-edge populations of S. pectinata and the potential role of temperature in shaping these populations as well. For these aims different biological traits were measured for a year in two non range-edge populations and two range-edge populations of S. pectinata. In general, non range-edge populations had higher densities and percentage of juveniles during November and smaller sizes than range-edge populations. The lack of significant differences in the reproductive traits between the two types of populations and the greater egg-ribbon lengths in range-edge populations suggests a high mortality of larvae or settled juveniles in the latter. Larval and juvenile stages are the most vulnerable stage of the life cycle of marine organisms and temperatures close to the tolerance limit may induce stress. Therefore, it is likely that lower water and air temperatures in the north could be responsible for the higher larval or juvenile mortality in range-edge populations of S. pectinata.