Phylogeny of the family Aglajidae (Pilsbry, 1895) (Heterobranchia: Cephalaspidea) inferred from mtDNA and nDNA

- We reconstructed the phylogeny of Aglajidae using mitochondrial and nuclear genes.
- Aglajidae and most taxonomic groupings within are monophyletic, in most analyses.
- Chelidonura appears to be paraphyletic, but support is low.
- Odontoglaja is the most basal Aglajidae confirming previous hypotheses.
- A reclassification of Aglajidae is probably necessary.

The family Aglajidae includes several species of benthic, carnivorous cephalaspidean sea slugs, which generally lack a radula, have an internal shell, a posterior shield with short to moderate caudal lobes, and sensory cilia present on the head. The present study reports a phylogenetic analysis of the Aglajidae based on the mitochondrial genes 16S and CO1 and the nuclear gene H3, including 160 specimens of 54 species, that confirms the monophyly of Aglajidae as well as most taxonomically established genera, with some exceptions. Although support values are low for some clades, the analysis recovered the following clades within the Aglajidae: Odontoglaja, Nakamigawaia, and Melanochlamys. Chelidonura appears to be paraphyletic and the monophyly of a Chelidonura-Navanax-Aglaja clade is strongly supported in the Bayesian analysis, plus three of the four individual gene trees (COI, COI without 3rd codon positions, 16S and H3). However, the relatively low levels of support in the maximum likelihood analyses prevent us from proposing the synonymization of Navanax and Aglaja with Chelidonura. Melanochlamys is the sister clade of Chelidonura + Aglaja + Navanax. Odontoglaja is basal to the rest of the Aglajidae, confirming previous hypotheses on the loss of the radula in Aglajidae. Nakamigawaia and Melanochlamys are monophyletic, and should be maintained as valid. The monophyly of Philinopsis is strongly supported in the Bayesian analysis and in three of the four individual gene trees. Further research on this group is necessary to further affirm the monophyly of Chelidonura + Aglaja + Navanax and Philinopsis. Based on the results of this phylogenetic analysis, a reclassification of the taxonomy of Aglajidae is probably necessary. Additional genes should provide more information and probably fully resolve this situation. The present molecular study (including ABGD species delineation analyses) suggests the existence of previously undetected species complexes that require additional study to determine the extent of undocumented biodiversity.