Molecular phylogeny of <i>Naineris</i> and <i>Protoaricia</i> (Annelida: Orbiniidae) with the reinstatement of <i>Theodisca</i>

Abstract Naineris is a genus of burrowing polychaete worms of the family Orbiniidae characterized by a rounded or truncated prostomium and a distinct thorax–abdomen division. Previous studies recovered Naineris as monophyletic, paraphyletic, or polyphyletic and have shown close relationships between Naineris and Protoaricia. In the present study, we provide the first comprehensive revision of Naineris using an integrative approach. Our molecular analysis includes 149 specimens of Naineris assigned to 25 species collected worldwide. Phylogeny (maximum likelihood and Bayesian inference) based on the combined matrix of two mitochondrial and one nuclear marker resulted in four well-supported clades, each also supported by morphological synapomorphies. Our results suggest polyphyly of Naineris, which we resolve by splitting the genus into two clades. The first clade includes the type species Naineris quadricuspida, in addition to Naineris uncinata, and represents Naineris s.s. Four more species are included in Naineris s.s. based on morphological data. The second clade, Theodisca reinstated, comprises all the species of Naineris included in the analysis together with species of Protoaricia, including the type species, Protoaricia oerstedii. Theodisca is divided into three monophyletic subgenera: T. (Theodisca), T. (Unitheodisca) subgen. nov. and T. (Polytheodisca) subgen. nov., each defined by morphological synapomorphies. Amended diagnoses and descriptions of both genera and three subgenera are provided.