The systematics of the amphidromous shrimp Macrobrachium americanum Spence Bate, 1868 (Decapoda: Caridea: Palaemonidae) from the Mexican Pacific slope

Abstract The amphidromous species of Macrobrachium Spence Bate, 1868 occurring on the Mexican Pacific slope (M. americanum Spence Bate, 1868, M. digueti (Bouvier, 1895), M. hobbsi Nates & Villalobos in Villalobos Hiriart & Nates Rodríguez, 1990, M. occidentale Holthuis, 1950 (Holthuis, 1950b), and M. tenellum (Smith, 1871)) show a disjunct distribution, with the abscence of records along about 2000 km of the coastal margins in the northern Gulf of California. Recent morphological and genetic studies using the mitochondrial genes 16S rRNA (16S) and cytochrome oxidase I (COI) show that individuals of the putative M. digueti, M. hobbsi, and M. occidentale from the Baja California Peninsula are conspecific to their respective taxonomic entities found along the Pacific slope of mainland Mexico. We review the systematics of M. americanum from the Mexican Pacific slope and found that individuals of putative M. americanum from the Baja California Peninsula belong to the same lineage of individuals from the Pacific slope of mainland Mexico based on newly generated fragments of the mitochondrial genes 16S (491 bp) and COI (548 bp). We present a systematic account for M. americanum, including a taxonomic treatment of the studied populations with a report of their genetic identity and phylogenetic relationships.