The systematics of the genus Branchipus Schaeffer, 1766 (Branchiopoda: Anostraca) has been based on morphological taxonomy only and thus remains poorly resolved or, at best, questionable. Among the seven species described in the genus, a detailed comparison of Branchipus schaefferi Fischer, 1834 with both B. pasai Cottarelli, 1969 and B. visnyai Kertesz, 1956 is necessary to clarify their status. The use of morphological characters and, in particular, the appearance of second antennae and antennal appendages in males still cause taxonomic confusion among these three species. Herein, we use two molecular markers (allozymes and mtDNA sequences) and scanning electron microscopy to determine consistent differentiation patterns and test for congruence with the shape of the genus diagnostic trait, the frontal shield. We analyzed specimens belonging to 11 populations and covering a wide geographic distribution: B. pasai from Italy, B. schaefferi from Spain and Morocco, and B. visnyai from Malta and Italy. The extent of genetic divergence among populations evaluated by allozyme variation at 13 enzymatic loci and a mtDNA marker suggests the existence of different taxa and the absence of gene flow between them. The molecular results, together with morphological observations, did not provide support for the existing subdivision in the three nominal species B. pasai, B. schaefferi, and B. visnyai and places the validity of previously proposed taxonomic groups in discussion.
