The potential of 'museomics' to revitalize taxonomy - a case study on aplacophoran Mollusca

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There is no doubt about the value of molecular data in systematics for testing established phylogenetic hypotheses and delineating species. Yet some clades remain inaccessible to molecular approaches, as recollection of fresh material is not always feasible, e.g. in the case of endangered species or deep-sea lineages. And depending on the available taxonomic knowledge, correctly assigning new specimens to valid species can be problematic. Correct assignment is assured when dealing with type material stored in natural history collections. But stored genetic resources remain underutilized despite recent pioneering studies which successfully demonstrate how vast amounts of genetic data (entire mitochondrial genomes and 'ultraconserved' elements) can be extracted from century-old type material stored in museum collections ('museomics'). Solenogastres (or Neomeniomorpha) form a small, neglected class of Mollusca with controversial phylogenetic placement and a crucial importance to understanding early molluscan evolution. Distributed mainly in the deep sea, knowledge of their species diversity remains scant. And due to a bulky and time-consuming taxonomic process requiring histological sectioning as well as radula and scleritome preparation for identification to family level and beyond, the majority of the newly collected material stays unidentified. Consequently, their potential to enhance our understanding of diversity, distribution patterns and biological interactions in the deep sea remains largely neglected. This study aims to revitalize the taxonomy of Solenogastres through the use of NGS-based 'museomics' via target capture of mitochondrial markers (ideally entire mitochondrial genomes) and 'conserved elements' or the nuclear genome from type material of all 264 valid species. We will select a range of fast-evolving markers and comparatively perform tree and pairwise-distance methods of molecular species delineation to test traditional, largely scleritome-based taxonomy. In the case of contradicting lines of evidence between molecular and morphological data, we will reinvestigate the microanatomy using modern histological and ultrastructural approaches. This integrative species delineation will be supplemented by the first comprehensive phylogenomic analyses on the systematic relationship of Solenogastres, ultimately leading to an overall renewed taxonomy of this clade of worm-molluscs. Solenogaster 'museomics' will serve as a cost-efficient showcase for the large-scale application of DNA hybridization capture from old type material stored in natural history collections for clades, whose taxonomy can neither be reliably accessed through traditional taxonomy via morphological characters nor through classical barcoding. The established multi-loci barcoding-library will serve to identify and delineate novel lineages in future biodiversity research reliably, while providing a molecular taxonomy well founded in the Linnaean System.