The family Ctenophthalmidae (Order Siphonaptera) has been considered as a 'catchall' for a wide range of divergent taxa showing a paraphyletic origin. In turn, Ctenophthalmus sp. (Ctenophthalmidae) includes 300 valid described taxa. Within this genus, males are easily distinguishable basing on the size, shape, and chaetotaxy of their genitalia; however, females show slight morphological differences with each other. The main objective of this work was to carry out a comparative morphometric, phylogenetic, and molecular study of two different subspecies: Ctenophthalmus baeticus boisseauorum and Ctenophthalmus apertus allani in order to clarify and discuss its taxonomic status. From a morphological and biometrical point of view, we found clear differences between modified abdominal segments of males of both subspecies and slight differences in the margin of sternum VII of all female specimens which did not correspond with molecular and phylogenetic results based on four different molecular markers (Internal Transcribed Spacer 1 and 2 of ribosomal DNA, and the partial cytochrome c oxidase subunit 1 and cytochrome b of mitochondrial DNA). Thus, we observed a phenotypic plasticity between both subspecies, which did not correspond with a real genotypic variability nor different environmental or ecological conditions. Basing on these results, we could consider that there are no solid arguments to consider these two 'morphosubspecies' as two different taxa. We propose that C. b. boisseauorum should be considered as a junior synonym of C. a. allani.
Keywords: Ctenophthalmus; Siphonaptera; molecular biology; ribosomal and mitochondrial DNA; taxonomy.