Further evidence for diversification within the Diogenes pugilator complex (Anomura, Diogenidae) in the Mediterranean and Black Seas

Abstract We document an unrecognised genetic lineage within the European hermit crab Diogenes pugilator species complex. Specifically, we propose the revalidation of the previously synonymised species D. ponticus , for specimens previously identified as D. pugilator from the Adriatic, Ionian, Aegean, and Black Seas. Analyses of the mitochondrial genes COI and 16S rRNA resulted in a clear genetic separation to East Atlantic and Western Mediterranean populations of Diogenes . Morphological analyses confirmed differences in the individuals assigned to D. ponticus compared to the congeners D. curvimanus and D. pugilator and thereby a concordance between molecular and morphological characters. Despite the relatively high morphological resemblance to D. armatus , the molecular differentiation and the remarkable geographic segregation within the species complex suggest at least one speciation or radiation event in the past, underlining the growing importance of molecular methods in the identification of species and evolutionarily significant units. Major oceanographic processes that are known to shape genetic variability and population genetic structure in the marine environment are pointed out as possible structuring factors for the observed intrageneric divergence. The evidence of long evolutionary independence is therefore considered sufficient to re-establish the validity of D. ponticus as a valid species in the northern-central and north-eastern Mediterranean Sea and the Black Sea and is redescribed accordingly.