Our aim was to delimit the taxonomic status of the snapping shrimp Alpheus lobidens De Haan, 1849, based on morphological and molecular analyses of the topotype material from Nagasaki (Japan). We provide a redescription, detailed illustrations, and molecular data. Through comparisons with close-related species, we also tested the taxonomic status of A. inopinatus Holthuis Gottlieb, 1958 and A. buckupi Almeida, Terossi, Araújo-Silva Mantelatto, 2013. We examined 74 specimens previously identified as A. lobidens, 84 specimens of A. buckupi, and 30 of A. inopinatus. The morphological analysis was based on the examination of 68 characters. The molecular analysis included mitochondrial gene sequences (16S) of 18 individuals: six A. lobidens, three A. buckupi, one A. inopinatus, and eight individuals of other species of Alpheidae. The morphological analysis revealed that A. lobidens sensu stricto is consistently distinct of A. lobidens sensu lato, A. inopinatus and A. buckupi. The genetic analyzes (Bayesian Inference and p-distance) corroborated the morphological results and showed a clear separation between them. The highest values of genetic divergence (p-distance) (19%) were observed between A. lobidens sensu stricto and A. buckupi, and between A. lobidens sensu stricto and A. lobidens sensu lato from Australia (Northern Territory). The lowest divergence (12%) occurred between A. lobidens sensu stricto and A. lobidens sensu lato from Marshall Islands. Based on our results, the occurrence of A. lobidens sensu stricto is currently restricted to the type locality in Japan, and A. inopinatus and A. buckupi are valid taxa. Delimiting A. lobidens sensu stricto is relevant since the name A. lobidens has been applied to cryptic species, resulting in a high unclear taxonomic state.
Keywords: Crustacea, Decapoda, alpheid, species complex, molecular systematics, 16S gene.