The phylogenetic position and taxonomic status of Sterechinus bernasconiae Larrain, 1975 (Echinodermata, Echinoidea), an enigmatic Chilean sea urchin

Sterechinus is a very common echinoid genus in benthic communities of the Southern Ocean. It is widely distributed across the Antarctic and South Atlantic Oceans and has been the most frequently collected and intensively studied Antarctic echinoid. Despite the abundant literature devoted to Sterechinus, few studies have questioned the systematics of the genus. Sterechinus bernasconiae is the only species of Sterechinus reported from the Pacific Ocean and is only known from the few specimens of the original material. Based on new material collected during the oceanographic cruise INSPIRE on board the R/V Melville, the taxonomy and phylogenetic position of the species are revised. Molecular and morphological analyses show that S. bernasconiae is a subjective junior synonym of Gracilechinus multidentatus (Clark). Results also show the existence of two genetically distinct subclades within the so-called Sterechinus clade: a Sterechinus neumayeri subclade and a subclade composed of other Sterechinus species. The three nominal species Sterechinus antarcticus, Sterechinus diadema, and Sterechinus agassizi cluster together and cannot be distinguished. The species Sterechinus dentifer is weakly differentiated from these three nominal species. The elucidation of phylogenetic relationships between G. multidentatus and species of Sterechinus also allows for clarification of respective biogeographic distributions and emphasizes the putative role played by biotic exclusion in the spatial distribution of species.