Congruence between morphology and molecular data supports the distinction between the snapping shrimps Alpheus...

The snapping shrimp Alpheus macrocheles (Hailstone, 1835b) is widely distributed across the Atlantic Ocean and was originally described from Hastings, England, based on a very brief description with limited morphological details and diagnostic illustrations. The morphologically similar A. amblyonyx Chace, 1972, type locality Quintana Roo, Mexico, is a western Atlantic taxon. The superficial description of A. macrocheles by Hailstone and the high similarity with A. amblyonyx has led to taxonomic confusion regarding the precise identification of these species. Thus, our objective was to reexamine these two species, based on a combined analysis of morphological-including a redescription for A. macrocheles and new morphological characterization of A. amblyonyx-and molecular data. In total, 42 morphological characters were analyzed, in addition to a phylogenetic analysis of 16S ribosomal RNA (rRNA) gene sequences. A Bayesian Inference analysis recovered A. macrocheles and A. amblyonyx as distinct clades supporting the taxonomic distinction between them. The tree topology suggests that A. macrocheles is more closely related to A. crockeri (Armstrong, 1941) and A. puapeba (Christoffersen, 1979) than to A. amblyonyx, which forms the sister group to a well-supported clade containing these three species. This contribution conclusively distinguishes between A. macrocheles and A. amblyonyx and points out the need for a comprehensive review involving all species of the larger A. macrocheles group.