Spermio-and embryotoxicities of Cu, Ag, Cd, and Hg were investigated in Paracentrotus lividus, the dominant echinoid species of the Mediterranean. Spermiotoxicity was studied by assessing the effects of sperm exposure on fertilization rate (FR) as well as on the induction of transmissible damages to the offspring. Embryotoxicity was studied by assessing developmental defects in larvae exposed to the tested metals throughout their development. Sperm exposures resulted in significant decreases of FR, depending on both metal concentration and duration of the exposure. Lowest spermiotoxic concentrations recorded when sperm were exposed for 75 min to the metals were 10 ฯช7 M Hg(II), 10 ฯช6 M Ag(I), 10 ฯช5 M Cu(II), and 10 ฯช5 M Cd(II). Tested metals did not exert any transmissible damage to spermatozoa that could result in larval malformations in the offspring, even for concentrations that dramatically reduced FR. Single-element exposures of embryos for 72 h resulted in developmental defects whose occurrence and severity showed a steep dose dependence, indicating that once a threshold is reached, any further increase in toxicant concentration rapidly enhances the impairment of target function(s). Those observations suggest the involvement of a saturable protective mechanism. Lowest observed embryotoxic concentrations of the metals were 10 ฯช7 M Hg(II), 2.5 ฯซ 10 ฯช7 M Ag(I), 5 ฯซ 10 ฯช7 M Cu(II), and 10 ฯช5 M Cd(II) and are in the range of concentrations reported in heavily polluted marine environments. Thus, the possibility of impairment of echinoid development actually exists in metal-contaminated marine environments, possibly threatening echinoid populations in those environments.