A new species of Stylochidae flatworm Imogine lateotentare is described from Botany Bay, eastern New South Wales, Australia. This flatworm is distinguished from other species in the same genus mainly by having small, transparent and inconspicuous tentacles, densely packed purplish pink flecks at the posterior of the dorsal surface, distinctive purplish red colour gonopores and continuous bands of numerous frontal and cerebral eyes. Feeding and reproductive behaviour in the laboratory are described. This flatworm was found closely associated with the barnacle Balanus variegatus (Darwin, 1854) on which it fed by extending its pharynx over the barnacle opercular and sucking out the flesh but ejecting the cirri. It consumed one Balanus variegatus in a 14-day observation period and it was observed feeding exclusively at night.