New molecular resources of Loimia borealis (Annelida, Terebellidae) based on genome-skimming and RNA-seq approaches, with insights into monophyly of the genus

The terebellid Loimia borealis Wang, Sui, Kou & Li, 2020 was first described from Shouguang, China, and its molecular data, consisting of partial mitochondrial genes (cox1 and 16S) and a partial nuclear gene (18S), were reported. In this study, small-sized specimens of L. borealis were collected near the type location, and the species’ morphological description is supplemented. Several commonly used genetic sequences, including the complete mitochondrial genome, complete nuclear high-copy genes (18S-ITS1-5.8S-ITS2-28S), and histone genes (H3, H4, H2B, and H2A), are also provided. Additionally, the transcriptome of L. borealis is assembled from data generated by RNA-seq. A Benchmarking Universal Single-Copy Orthologs (BUSCO) assessment showed high completeness of the transcriptome, with 97.5% (655/672) of the metazoan conserved orthologous genes. We provide an easier pipeline to facilitate the mining of molecular markers from genome-skimming sequencing data. The monophyly of Loimia is supported when combined with partial mitochondrial gene markers (cox1 and 16S) and partial nuclear genes (18S, 28S, and H3), but not by individual genes. The nodes in the phylogenetic trees based on 13 protein-coding genes (13 PCGs) and 2 mitochondrial rRNA genes were well supported, with most showing maximum bootstrap support and posterior probability. The current classification of Terebelliformia and Cirratuliformia is also supported.