A revision of the textricellin spider genus Raveniella (Araneae: Araneoidea: Micropholcommatidae): Exploring patterns of phylogeny and biogeography in an Australian biodiversity hotspot

South-western Western Australia is a biodiversity hotspot, with high levels of local endemism and a rich but largely undescribed terrestrial invertebrate fauna. Very few phylogeographic studies have been undertaken on south-western Australian invertebrate taxa, and almost nothing is known about historical biogeographic or cladogenic processes, particularly on the relatively young, speciose Quaternary sand dune habitats of the Swan Coastal Plain. Phylogeographic and taxonomic patterns were studied in textricellin micropholcommatid spiders belonging to the genus Raveniella Rix Harvey. The Micropholcommatidae is a family of small spiders with a widespread distribution in southern Western Australia, and most species are spatially restricted to refugial microhabitats. In total, 340 specimens of Raveniella were collected from 36 surveyed localities on the Swan Coastal Plain and 17 non-Swan Coastal Plain reference localities in south-western Western Australia. Fragments from three nuclear rRNA genes (5.8S, 18S and ITS2), and one mitochondrial protein-coding gene (COI) were used to infer the phylogeny of the genus Raveniella, and to examine phylogeographic patterns on the Swan Coastal Plain. Five new species of Raveniella are described from Western Australia (R. arenacea, sp. nov., R. cirrata, sp. nov., R. janineae, sp. nov., R. mucronata, sp. nov. and R. subcirrata, sp. nov.), along with a single new species from south-eastern Australia (R. apopsis, sp. nov.). Four species of Raveniella were found on the Swan Coastal Plain: two with broader distributions in the High Rainfall and Transitional Rainfall Zones (R. peckorum Rix Harvey, R. cirrata); and two endemic to the Swan Coastal Plain, found only on the western-most Quindalup dunes (R. arenacea, R. subcirrata). Two coastally restricted species (R. subcirrata, R. janineae) were found to be morphologically cryptic but genetically highly distinct, with female specimens morphologically indistinguishable from their respective sister-taxa (R. cirrata and R. peckorum). The greater Perth region is an important biogeographic overlap zone for all four Swan Coastal Plain species, where the ranges of two endemic coastal species join the northern and south-western limits of the ranges of R. peckorum and R. cirrata, respectively. Most species of Raveniella were found to occupy long, highly autapomorphic molecular branches exhibiting little intraspecific variation, and an analysis of ITS2 rRNA secondary structures among different species of Raveniella revealed the presence of an extraordinary hypervariable helix, ranging from 31 to over 400 nucleotides in length.