Despite discovery more than 100 years ago and documented global occurrence from shallow waters to the deep sea, the life cycle of the enigmatic crustacean y-larvae isincompletely understood and adult forms remain unknown. To date, only 2 of the 17 formally described species, all based on larval stages, have been investigated using an integrative taxonomic approach. This approach provided descriptions of the morphology of the naupliar and cyprid stages, and made use of exuvial voucher material and DNA barcodes. To improve our knowledge about the evolutionary history and ecological importance of y-larvae, we developed a novel protocol that maximises the amount of morpho-ecological and molecular data that can be harvested from single larval specimens. This includes single-specimen DNA barcoding and daily imaging of y-nauplii reared in culture dishes, mounting of the last naupliar exuviae on a slide as a reference voucher, live imaging of the y-cyprid instar that follows, and fixation, DNA extraction, amplification and sequencing of the y-cyprid specimen. Through development and testing of a suite of new primers for both nuclear and mitochondrial protein-coding and ribosomal genes, we showcase how new sequence data can be used to estimate the phylogeny of Facetotecta. We expect that our novel procedure will help to unravel the complex systematics of y-larvae and show how these fascinating larval forms have evolved. Moreover, we posit that our protocols should work on larval specimens from a diverse array of moulting marine invertebrate taxa.

Mastigusa is a genus of small palearctic spiders that has recently been moved to the family Cybaeidae after the first inclusion of the genus in a phylogenetic matrix. Three species are currently recognised: M. arietina, M. lucifuga and M. macrophthalma. The status and delimitation, though, has always been problematic due to inconsistency in the characters used to discriminate between these, leading to great confusion in identity and distribution. We present a detailed morphological redescription of the genus and a taxonomic revision of the included species by the combined use of morphological data and molecular species-delimitation techniques based on the mitochondrial COI gene. The status of the three currently described species has been reevaluated and Mastigusa diversa was revalidated based on material from the Iberian Peninsula, North Africa and the United Kingdom. The distribution of Mastigusa species is updated based on novel taxonomic considerations, and comments on the natural history and ecological differences observed in the species are provided.