Post-mortem examination of a fin whale Balaenoptera physalus stranded in the Mediterranean Sea led to the finding of Bolbosoma balaenae for the first time in this basin. In this work, we describe new structural characteristics of this parasite using light microscopy and scanning electron microscopy approaches. Moreover, the molecular and phylogenetic data as inferred from both ribosomal RNA 18S-28S and the mitochondrial DNA cytochrome oxidase c subunit 1 (cox1) for adult specimens of B. balaenae are also reported for the first time. Details of the surface topography such as proboscis's hooks, trunked trunk spines of the prebulbar foretrunk, ultrastructure of proboscis's hooks and micropores of the tegument are shown. The 18S + 28S rRNA Bayesian tree (BI) as inferred from the phylogenetic analysis showed poorly resolved relationships among the species of Bolbosoma. In contrast, the combined 18S + 28S + mtDNA cox1 BI tree topology showed that the present sequences clustered with the species of Bolbosoma in a well-supported clade. The comparison of cox1 and 18S sequences revealed that the present specimens are conspecific with the cystacanths of B. balaenae previously collected in the euphausiid Nyctiphanes couchii from the North Eastern Atlantic Ocean. This study provided taxonomic, molecular and phylogenetic data that allow for a better characterization of this poor known parasite.
Keywords: Balaenoptera physalus; Bolbosoma balaenae; Mediterranean Sea; fin whale; mitochondrial DNA cox1; phylogenetic analysis; ribosomal RNA 18S-28S.