Rhopalophthalmus tartessicus sp. nov. (Crustacea: Mysidacea), a new mysid species from the Guadalquivir estuary (SW Spain)

The first representative of the genus Rhopalophthalmus in European waters, Rhopalophthalmus tartessicus sp. nov., is described from specimens sampled in the Guadalquivir estuary (southwestern Spain). At first identified as the Algerian species Rhopalophthalmus mediterraneus Nouvel, 1960, the new mysid species can be distinguished from its closest relative by its higher number of articles on the carpopropodus of the third to seventh thoracic endopods, by the well hook-shaped eighth thoracic endopod of the male, by the slender eighth thoracic endopod of the female, and by the smaller antennal scale and telson. Its geographical distribution appears restricted to estuarine habitats in southwestern Spain. Its swimming behaviour, with the ventral side facing upwards, is unusual in mysids. An updated identification key for the 19 known species in the genus, including information on the respective geographical distribution and habitat, is presented.