Molecular Characterization of Philometra obladae (Nematoda: Philometridae) in Juvenile Oblada melanura (Linnaeus, 1758) from the Tyrrhenian Sea off Sicily, Italy.

Philometra obladae is a nematode belonging to the family Philometridae. It was morphologically described for the first time in 2008 in Oblada melanura. To date, few data on the molecular characterization of Philometridae have been reported. The aim of the present study was to molecularly characterize Philometra obladae in O. melanura inhabiting the Tyrrhenian coasts off Sicily, Italy. In July 2023, five nematodes were found and morphologically identified as Ph. obladae from the celomic cavity of four O. melanura specimens. Genomic DNA from four nematodes was extracted and two molecular markers, the ribosomal 18S rRNA and the mitochondrial cox1, were amplified using polymerase chain reaction. The sequences obtained were aligned using the MUSCLE algorithm and were used for phylogenetic analyses. Partial sequences of both markers were submitted to GenBank. Phylogenetic trees for both markers resulted in very similar topologies with high posterior probabilities and bootstrap values. Comparisons of our results indicated that Ph. obladae is related to the sequences of other Philometridae isolated from different hosts and different geographic areas. Phylogenetic analysis was carried out to compare the sequences of Ph. obladae with other marine Philometridae, which allowed for the molecular characterization of Ph. obladae as an independent species for the first time.