Phylogenetics of Lepidonotopodini (Macellicephalinae, Polynoidae, Annelida) and Comparative Mitogenomics of Shallow-Water vs. Deep-Sea Scaleworms (Aphroditiformia)

Within Polynoidae, a diverse aphroditiform family, the subfamily Macellicephalinae comprises anchialine cave-dwelling and deep-sea scaleworms and is emended herein to include all genera previously placed in the subfamily Lepidonotopodinae. Additionally, the tribe Lepidonotopodini is applied to a well-supported clade that exclusively inhabits deep-sea chemosynthetic-based ecosystems. These and other taxonomic changes are based on the analysis of newly sequenced genome skimming data for 30 deep-sea scaleworms and one comparatively shallow living relative, Eulagisca gigantea. The data were bioinformatically assembled into complete mitogenomes with high read coverage and resolution. When analyzed alongside pre-existing scaleworm mitogenomes, deep-sea scaleworms were found to exhibit increased gene order rearrangement events, a relaxed purifying selection of mitochondrial protein-coding genes, and a positive selection of amino acid sites compared to their shallow-water relatives. Furthermore, the inclusion of skimming data for already-known Lepidonotopodini species allowed for the assembly of a molecular dataset with increased coverage and taxon sampling. The phylogenies obtained support the erection of five new genera and the amendment of four pre-existing ones.