The acute lethal toxicity of copper, as well as its sublethal effect on molting, was studied on larval and postlarval stages of the pinnotherid crab Tunicotheres moseri. The most sensitive stage was zoea I, presenting a significant mortality above 0.5 microg x L(-1). Abnormal setation of the maxillipeds was observed in zoeae II moulted from zoeae I exposed to 100 microg x L(-1) and higher copper concentrations, causing a reduced swimming activity of the larvae. This pathology could be reverted after molting of affected zoea II to megalopa, which would be the first report in crustacean larvae that states the possibility of reverting morphological abnormalities after molting. For zoeae II and megalopae, the inhibition of molting and high mortality was registered at 1,000 microg x L(-1). The effect of copper on the duration of the larval and postlarval stages was differential: It retarded the duration of the stage zoea I, did not modify that of zoea II, and accelerated the ecdysis of the megalopae to first crab. However, precocious molting to megalopae was associated with a smaller body size at the concentration of 100 microg x L(-1). This differential effect of copper on the larval stages throughout the larval development could be ecologically relevant. Because of their lecithotrophia, their short developmental period, their good survival in control conditions, and the high sensitivity showed to copper (especially zoea I), larvae of T. moseri have shown that they are an excellent model for studying the effect of pollutant on survival, molting rate, growth, and morphogenetic changes during development.