Modernin situsurvey technologies such as crewed submersibles, remotely-operated vehicles (ROVs), towed camera arrays, and visual/video plankton recorders (VPRs) were used to characterize the dominant anthomedusan species off the eastern seaboard of Japan. Notes on the taxonomy, distribution, behaviour and interspecies interactions are presented for the four observed species:Euphysa japonica, E. flammea, Calycopsis nematophoraandPandea rubra. A new generic definition for the genusCalycopsisis proposed. The possibility of run-on, cascading detrimental effects of oceanic acidification on midwater ecosystems was identified from observations made during the present study.