Diopatra neapolitana and Diopatra marocensis from the Portuguese coast: Morphological and genetic comparison

This paper reports the presence of Diopatra marocensis in European waters, for which Diopatra neapolitana was the only species recognized until recently. Both species coexist in transitional waters, where D. marocensis may be mistaken for young specimens of D. neapolitana. The population of D. marocensis studied in the coastal shelf can be traced back to 1997 and is increasing in density, apparently benefiting from a local anthropogenic organic enrichment source.This study emphasizes the main morphological characteristics that allow discriminating the two species and uses a molecular approach through the mitochondrial DNA genes 16S rDNA and COI (cytochrome c oxidase subunit I) analysis to confirm their distinction. The percentage of nucleotides divergence of the 16S and COI genes between the two species was 14% and 17%, respectively. The nucleotide sequence was conserved among all specimens of the same species for 16S gene, and the differences observed between individuals of the same species for the COI gene always corresponded to a silent alteration with no amino acid change. The nucleotide sequences of the two genes of both species were also compared to the sequences of Diopatra aciculata deposited in the EMBL database. The divergence values between Diopatra marocensis and D. aciculata were 14% and 18% for 16S and COI, respectively whereas between Diopatra neapolitana and D. aciculata were 1% and 5% for 16S and COI, respectively. Phylogenetic analysis was performed to deduce relationships among the Diopatra species studied. This analysis showed that D. marocensis and D. neapolitana are in different clades and thus could be considered different species, whereas D. aciculata and D. neapolitana are in sister clades thus emphasising their similarities, already noticed at a morphological level.