4 DISCUSSION
The enigmatic facetotectans (commonly referred to as “y-larvae”) are a severely understudied crustacean subclass, and the notable dearth of molecular resources and published morphological voucher data concerning them has impeded reconstruction of the group’s evolutionary history of (Pérez-Losada et al., 2002, 2009; Kolbasov et al., 2022). To overcome the challenges inherent in inferring systematic relationships based on unvouchered, unphotographed specimens, as exemplified by Pérez-Losada et al., (2002, 2009) and Gallego et al., (2015), we developed a cheap, fast, and voucher-preserving protocol capitalizing on the widely-used DNeasy™ extraction kit. Our aim was to develop a rearing and extraction protocol that maximizes morphological and molecular information for single y-larval specimens spanning what is emerging as a complex and wide phylogenetic range (Olesen et al., 2022; Kolbasov et al., 2022; Dreyer et al., submitted; data herein). By relying on a suite of light microscopic images of live larvae (Olesen et al., 2022) and by developing primers targeting both nuclear and mitochondrial genomic markers, we demonstrate a way to infer phylogenetic relationships based on larval instars of a crustacean taxon with a complicated and partly unknown lifecycle. In the following we discuss three central topics related to the development of these new molecular resources: (1) The efficacy and usefulness of the new primers and the two new DNA extraction methods, (2) how three overall protocols and their varying yields of morphological resolution may affect systematic accounts and future taxonomic classification, and finally (3) interesting features of the preliminary phylogeny, for example the molecular and biogeographical extent of morphotypes, and how to use such information in building a taxonomy that, for now, must rely entirely on larval stages. We believe that our protocols should also work on other molting invertebrate larvae.