Integrative taxonomy of <i>Peniculus</i>, <i>Metapeniculus</i>, and <i>Trifur</i> (Siphonostomatoida: Pennellidae), copepod parasites of marine fishes from Chile: species delimitation analyses using DNA barcoding and morphological evidence

Pennellidae is a family of copepod parasites of widely distributed marine fishes. The pennellid species are usually morphologically differentiated by cephalothorax, neck, trunk, and abdomen shape. These characters, however, show high polymorphism and therefore using only this type of data, delimitation at species level of this genus is difficult. In this study, we explored the genetic distances calculated from sequences of a DNA barcoding marker (COI mt) (678 base pairs). We also explored the genetic distances of 25 <i>Peniculus</i> specimens associated within nine marine fish species, four <i>Metapeniculus</i> specimens associated within one marine fish species, and four <i>Trifur</i> specimens associated within one marine fish species. All specimens were collected in Antofagasta Bay, Chile and were calculated from sequences of a DNA barcoding marker (COI mt) (678 base pairs). The genetic distance among the <i>Peniculus</i> specimens was 0.95% from the different host species, the <i>Metapeniculus</i> specimens distance was 0.44% and the <i>Trifur</i> specimens was 2.25%. Genetic difference between <i>Peniculus</i> and <i>Metapeniculus</i> was 17.86% and <i>Peniculus</i> differ from <i>T</i>. <i>tortuosus</i> by 18.16%. We analysed the barcoding gene fragment using Bayesian Inference (BI) for phylogenetic reconstruction using three outgroups. Based on the phylogenetic analysis an ultrametric tree was built and a general mixed Yule-coalescent (bGMYC) model was conducted for species delimitation. Morphometrics analyses were made with Bayesian statistics. Mean and credibility limit (95%) for each parameter was calculated. Results show that based on morphology the individuals collected can be assigned to <i>P.</i> cf. <i>fistula</i> von Nordmann, 1832, <i>Metapeniculus antofagastensis</i> Castro-Romero &amp; Baeza-Kuroki, 1985, and <i>Trifur</i> cf. <i>tortuosus</i> Wilson, 1917. High morphological polymorphism was observed for the lineage of <i>Peniculus</i> associated to several host species of marine fishes. Similar results were obtained for <i>Trifur</i> cf. <i>tortuosus</i> parasites on Chilean marine fishes.