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Mesalina are small diurnal lacertid lizards inhabiting arid areas from North Africa to northwestern India. Previous phylo- genetic studies have shown the existence of several species complexes within the genus, some of them with high levels of undiscovered diversity. In the present study, we carry out an integrative systematic revision of the Mesalina guttulata spe- cies complex using both molecular and morphological data from across its entire distribution range in North Africa, the Middle East and Arabia. The results of the genetic analyses indicate that M. guttulata and M. bahaeldini are two allopatric sister taxa separated by the Suez Canal and that the species complex includes a further three unnamed deep phylogenetic lineages, two of them restricted to southern and southwestern Arabia and described herein as Mesalina austroarabica sp. nov. and Mesalina arnoldi sp. nov., respectively. As a result of the lack of enough material, the third deep lineage, distrib- uted across Kuwait, Saudi Arabia and Jordan, is provisionally left undescribed. The two newly described species are char- acterized by their size, scale counts and tail coloration, as well as differences at the three mitochondrial and one nuclear gene analyzed in the present study.

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Background The lacertid genus Mesalina has been the subject of several phylogenetic and biogeographic studies as well as taxonomic revisions within the last decade. The genus is partitioned into seven main clades, some of which represent species complexes of morphologically very similar species. The Mesalina guttulata species complex is one such case. This complex currently comprises four described species that occur through Arabia and northern Africa, however, the presence of a cryptic species in Saudi Arabia, Kuwait, and Jordan was pointed out recently. For this study, we collected new material of the various species of the M. guttulata complex, including the undescribed lineage from across Saudi Arabia. We carried out multilocus phylogenetic analyses using three mitochondrial and three nuclear markers and analysis of morphological data to verify whether the undescribed lineage deserves a species rank.
Results The results show that the lineage is clearly genetically separated from the other species of the complex and shows morphological differentiation from the other species. Therefore, we describe it herein as a new species, Mesalina cryptica sp. nov.
Conclusions We contribute to the taxonomy of Arabian lacertid lizards by describing a new species distributed in central Saudi Arabia, with isolated populations occurring in Kuwait and Jordan. Despite its large range, the species is genetically and morphologically homogeneous. The gap in its distribution between the Jordan and Saudi Arabia populations is ascribable to the paucity of sampling along the Saudi/Iraqi border.
Keywords Lizards, Mesopotamia, Middle East, Sauria, Squamates, Reptiles, Taxonomy