Phylogenetic tree. Relationships within the genus Onchidium based on COI and 16S sequences. Numbers above branches are the bootstrap values (Maximum Likelihood analysis) and below are the posterior probabilities (Bayesian analysis); only significant numbers (> 80% and > 0.9) are indicated. Onchidella and Peronia sequences serve as outgroups. Numbers for each individual correspond to unique identifiers in our DNA collection. All sequences of Onchidium specimens are new, with the exception of the specimens from China which were all misidentified as Onchidium “struma” by Sun et al. (2014). Information on individually-identified specimens can be found in the additional material examined and in Table 1.