Molecular phylogeny of European Runcinida (Gastropoda, Heterobranchia): the discover of an unexpected pool of complex species, with special reference to the case of Runcina coronata

Abstract Runcinida is a small heterobranch order of sea slugs with 61 known species distributed worldwide across temperate and tropical latitudes with two established families (Ilbiidae and Runcinidae). Little is known about the phylogenetic relationships within Runcinida. Here, we present the first molecular phylogeny of the order with an emphasis on European species and we discuss the taxonomic status of the type species Runcina coronata. Molecular phylogenetics based on the mitochondrial genes cytochrome c oxidase subunit I and 16S rRNA and nuclear gene histone H3 is used to investigate relationships between species. Detailed morpho-anatomical worked was additionally employed to study Runcina coronata. Our results suggest the monophyly of Runcinida and showed that Runcina coronata is a complex of four species, namely: R. coronata proper, R. aurata and two new species here formally described (R. caletensis sp. nov. and R. tingensis sp. nov.).