Bisphenol A(BPA) is an organic compound present in plastic products that is released into the environment after degradation. BPA is both a teratogenic substance and an endocrine disruptor. The phylogenetic position of tunicates as sister group of vertebrates and their cosmopolitan distribution in marine ecosystems make them reliable model organisms for ecotoxicology bioassays. We tested the effects of different concentration of BPA (0.1, 0.5, 1, 5, 10, and 20 \u3bcM) on sperm viability, fertilization and embryogenesis of two ascidian species, Phallusia mammillata and Ciona intestinalis. We evaluated the type and the incidence of induced malformations. Then we focused on the effects on the nervous system performing animmunostaining of central nervous system (CNS) and whole mount in situ hybridization (WISH) with neural specific markers. Exposure of sperm to BPA did not influence fertilization rate. Co-exposure of eggs and sperm to concentrations higher than 5\u3bcM caused incomplete division of zygotethat did not develop further. In P. mammillata, embryonic development was altered by 20\u3bcM BPA causing a severe phenotype with malformed sensory organs in almost all treated larvae. In C. intestinalis 20 \u3bcM BPA was lethal, while 10 \u3bcM concentration caused alteration to the sensory organs, indicating that C. intestinalis is less tolerant to BPA. Nervous system is a target of BPA action that caused an altered pattern of neural fibers. WISH with Ci-GAD and Ci-TH showed an alterationof dopaminergic and GABAergic cells after exposureto 10 \u3bcM BPA. These results showed that the most sensitive process to BPA is the first cell division. After 2-cell stage, higher concentrations are required to alter the development. BPA confirmed its teratogenic effects on ascidians and its interference with CNS development
