This thesis investigates the embryonic and larval responses to changes in hydrostatic pressure and temperature in four species of shallow-water invertebrates. Chapters 2 and 3 describe the results obtained for echinoid species. Results from Psammechinus miliaris are similar to previous work on echinoids. Despite the negative effects of hydrostatic pressures and low temperatures on embryonic development, larvae of Psammechinus miliaris were able to tolerate hydrostatic pressure and temperatures conditions that prevail far beyond the depth limit of the adult. Differences in temperature/pressure effects on dispersal stages between a northern and a southern population of Echinus esculentus were also investigated. The results suggest that the northern population is better adapted to low temperature. Chapter 4 and 5 focus on Patellidae (Gastropoda) species. Increasing hydrostatic pressure and low temperature had strong negative effects on trochophores of Patella vulgata and Patella ulyssiponensis. These results do not conform to previous results in this field and show that many more taxonomic groups need to be investigated before we know how widespread, among shallow-water invertebrates, is the physiological potential for larval migration into deep sea. The implications of larval temperature tolerances for latitudinal distributions are also discussed.