Larval and early postlarval shell morphology and morphometry of the bivalves Venus antiqua, Mulinia edulis, Ensis macha and Hiatella solida were studied. The specimens examined were obtained from plankton samples and/or from experimental laboratory cultures. The size ranges of the specimens studied were: 123-370 mu m in V. antiqua, 140-580 mu m in M. edulis, 157-670 mu m in E. macha and 145-1270 mu m in H. solida. The shell features analyzed were: general shape, umbo, shoulders, provinculum, and hinge lateral system. The total shell length and height, length of shoulders, provinculum and prodissoconch I and II lengths were measured. V. antiqua and M. edulis shells have similar appearance and provinculum; they differ only in the shape of the shoulders and in the lateral hinge system. E. macha and H. solida are clearly distinguishable from the other species studied. Each species showed characteristics of the genus and family to which they belong; only M. edulis differed from other species of the same genus in its provincular structure, umbo shape and size at which the ligament develops. All species exhibited allometric growth, with significant different growth rates ( P < 0.05) in both developmental stages. The traditional identification method based on shell morphology is still a valid and indispensable tool for the recognition of early life stages of bivalves collected in plankton and benthos although complementary identification techniques based on DNA analysis are strongly recommended.