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.