AHR and pulmonary arterial hypertension: To the best of our knowledge, this is first report of its kind on Ciona intestinalis type A. Moreover, we denoted the expression of Ci-AhR during metamorphosis; in particular, tissue distribution of Ci-AhR was denoted in juvenile Ciona. These findings provide basic information on the molecular mechanism underlying PAH action and the biological function of AhR in marine invertebrates.