Updated and annotated checklist of the opisthobranch molluscs (excluding Thecosomata and Gymnosomata) from the Azores archipelago (North Atlantic Ocean, Portugal)

The literature available on the opisthobranch molluscs of the Azores archipelago is reviewed in this study. A critical discussion is done on some of the most recent papers concerning this subject. A summary of the opisthobranch species from the Azores is presented. The opisthobranch fauna (excluding the planctonic Thecosomata and Gymnosomata) comprises 107 identified species distributed among six orders, Cephalaspidea s.l.: 50, Anaspidea: 5, Tylodinoidea: 2, Pleurobranchoidea: 6, Sacoglossa: 4 and Nudibranchia: 40.