Investigating the taxonomy and systematics of marinewood borers (Bivalvia: Teredinidae) combining evidence from morphology, DNA barcodes and nuclear locus sequences

Marine wood-boring teredinids, some of the most destructive wood borers in the sea, are a particularly difficult group to identify from morphological features. While in most bivalve species shell features are used as diagnostic characters, in the teredinids shell morphology shows high intraspecific variation and thus identification is based almost entirely on the morphology of the pallets. In the present study we aimed at improving `taxonomic resolution' in teredinids by combining morphological evidence with mitochondrial and nuclear DNA sequences, respectively Cytochrome c oxidase subunit I and small subunit rRNA 18S gene, to generate more rigorous and accessible identifications. DNA barcodes of Atlantic and Mediterranean populations of Lyrodus pedicellatus diverged by similar to 20\%, suggesting cryptic species in the morphospecies L. pedicellatus. The low intraspecific divergence found in barcodes of specimens of Nototeredo norvagica (0.78\%) confirms that Atlantic and Mediterranean forms of N. norvagica, the latter sometimes reported as Teredo utriculus, are the same species. Teredothyra dominicensis was found for the first time in the Mediterranean. A match was obtained between our 18S sequences and sequences of T. dominicensis from Netherlands Antilles, confirming that T. dominicensis in the Mediterranean is the same species that occurs in the Caribbean. There were differences in 18S sequences between Bankia carinata from the Mediterranean and Caribbean, which may indicate cryptic species