Tightening the girdle: phylotranscriptomics of Polyplacophora

Abstract

The phylogenetic relationships within the molluscan class Polyplacophora (chitons) have been studied using morphology, traditional Sanger markers and mitogenomics, but, to date, no analysis has been carried out using transcriptomic and genome-wide data. Here, we leverage the power of transcriptomes to investigate the chiton phylogeny to test current classification schemes and the position of Callochitonidae, a family whose phylogenetic position and taxonomic assignation are uncertain because of conflicting results from past studies. Using multiple data matrices with different taxon occupancy thresholds and inference methods, including both concatenated and coalescence-based approaches, we find a consistent resolution of the chiton phylogeny. Our results support a system with the orders Lepidopleurida, Chitonida and Callochitonida, with the latter two as sister groups. This resolution is compatible with recent mitogenomic results and rejects the position of Callochiton as a member of Chitonina.