The scale-worm family Iphionidae consists of four genera. Of these, Thermiphione has two accepted species, both native to hydrothermal vents in the Pacific Ocean; T. fijiensis Miura, 1994 (West Pacific) and T. tufari Hartmann-Schröder, 1992 (East Pacific Rise). Iphionella is also known from the Pacific, and has two recognized species; Iphionella risensis Pettibone, 1986 (East Pacific Rise, hydrothermal vents) and I. philippinensis Pettibone, 1986 (West Pacific, deep sea). In this study, phylogenetic analyses of Iphionidae from various hydrothermal vent systems of the Pacific Ocean were conducted utilizing morphology and mitochondrial (COI and 16S rRNA) and nuclear (18S and 28S rRNA) genes. The results revealed a new iphionid species, described here as Thermiphione rapanui sp. n. The analyses also demonstrated the paraphyly of Thermiphione, requiring Iphionella risensis to be referred to the genus, as Thermiphione risensis (Pettibone, 1986).