Phylogenomics confirms monophyly of Nudipleura (Gastropoda: Heterobranchia)

Abstract

The sister taxon of one of the most diverse and pharmacologically important heterobranch gastropod groups, Nudibranchia, is unclear. Pleurobranchomorpha have been recovered sister to Nudibranchia in most molecular phylogenetic studies to date, forming a clade called Nudipleura. However, this relationship has not been consistently recovered; some phylogenomic studies have recovered Nudipleura as a paraphyletic group, but transcriptome data have been available from only one representative of Pleurobranchomorpha to date. Here, we supplemented the paucity of data available for Pleurobranchomorpha by sequencing the transcriptome of Bathyberthella antarctica Willan & Bertsch, 1987 and analysing transcriptomes and genomes from a total of 27 gastropod species, inferring the phylogeny of Heterobranchia based on 993 genes. Consistent with analyses of datasets dominated by 18 S rDNA and recent phylogenomic studies, all of our analyses unequivocally support Nudipleura, recovering Nudibranchia as sister to Pleurobranchomorpha with maximal support. Our study supports previous hypotheses that nudipleurans evolved from a common ancestor with an androdiaulic reproductive system, a blood gland and a secondarily lost osphradium.