A new large violin spider from Argentina, with a discussion on the homology and evolution of female genital structures in Loxosceles (Araneae: Sicariidae)

Abstract

Violin spiders are an old, diverse genus of spiders, which includes medically significant species. Among its members, the Neotropical laeta group is particularly notable, as it includes the largest spiders of the genus, such as Loxosceles laeta (Nicolet). In this paper, I describe a new species belonging to this group, Loxosceles galianoa, sp. nov., from male and female specimens collected in the dry Argentinean north-west. The new species is the southernmost native member of the laeta group, and its phylogenetic placement is confirmed by a novel phylogenetic analysis based on molecular data and a taxon sampling including members of all Loxosceles species groups. The morphology of the endogyne of the new species prompted me to survey and characterise the morphological diversity of the female genitalia in Loxosceles. I review the homologies of the parts of the female genitalia in this genus. I argue that an enlarged uterus externus with a narrowed opening is synapomorphic for the laeta species group, whereas in the lineage containing the rufescens and gaucho groups the uterus externus may be sclerotised and bear numerous deep transversal ridges. I here hypothesise that Loxosceles is an example of a clade where female genital morphology is more diverse and has accumulated more morphological novelties than that of males. The geographic origin of the medically significant Loxosceles laeta is briefly discussed. Although this species is commonly referred as the ‘Chilean recluse spider’, I here argue that this species most likely originated in Peru and has been introduced to other South American countries by human action. The type material of Loxosceles accepta Chamberlin, 1920 is examined and illustrated. Loxosceles gaucho Gertsch, 1967 is newly recorded from Argentina and Paraguay.