In this study, we investigate the feasibility of developing a new behavioural toxicity bioassay (Swimming Speed Alteration test—SSA test) with larvae of Balanus amphitrite (Crustacea Cirripedia). This organism was chosen as a model for different reasons: it is present all over the world, simple to be reared, easily available, and also because barnacles play an important role in the coastal ecosystem. In addition, all the operations related to the rearing and test execution are comparatively cheap. This bioassay was performed with several classes of chemical pollutants (antifouling biocides, neurotoxic pesticides, and heavy metals) and with environmental samples (sediment elutriates). The measurement of swimming speed, by means of video-graphic techniques, proved to be a valid instrument in highlighting the sub-lethal levels of toxicity caused by the different tested samples. In conclusion, the SSA test is …