Amphinomida is an ‘isolated’ clade within the polychaete group Aciculata and traditionally includes the families Amphinomidae, Archinomidae and Euphrosinidae. Archinomidae were erected for a single species, the hydrothermal vent polychaete Archinome rosacea. Originally, A. rosacea was assigned to Euphrosinidae although it shares more morphological similarities with Amphinomidae. In this study we assess the position of Archinome, Euphrosinidae and Amphinomidae by using molecular data from nuclear 18S rDNA and 28S rDNA. Parsimony, maximum likelihood and Bayesian analyses are performed on the nucleotide datasets covering in total 19 terminals from Amphinomidae, Euphrosinidae, Archinomidae and outgroups. Our results conclusively show that Euphrosinidae and Amphinomidae are sister taxa and that Archinome is sister to Chloeia within Amphinomidae. Based on these results the family name Archinomidae is treated as a junior synonym of Amphinomidae.
