Specimens of Belisana coblynau Huber & Clark, sp. nov. were collected by scrape sampling. This method is commonly used to collect troglofauna, particularly when sampling for environmental impact assessments associated with mining (Halse and Pearson 2014). Due to regulations by the Environment Protection Authority (EPA) in Western Australia, new bores that are drilled for mining exploration purposes can only be sampled after six months; as a result, the boreholes were at least six months old at the time of sampling. A weighted net was lowered down uncased holes (diameter 150 mm). The net was lowered to the base of the hole or to the groundwater table (~35 m below ground level) and then drawn slowly back to the surface, “scraping” the net up the wall of the bore, knocking any fauna into the net. This was repeated four times, once on each of the four sides of the bore (i.e., north, south, east, and west). The samples were washed into a 250 ml plastic vial and preserved in 100% ethanol. Samples were stored at 4 °C. Buitinga ifrit Huber & Cazanove, sp. nov. was collected manually; specimens were preserved in 70% ethanol and stored at room temperature.

The specimens are deposited in the following institutions: Museum d’Histoire Naturelle de La Réunion, Saint Denis (MHNR); Western Australian Museum, Perth (WAM); and Zoological Research Museum Alexander Koenig, Bonn (ZFMK).

Taxonomic descriptions follow the style of publications on related Pholcidae taxa (i.e., Huber 2003, 2005; based on Huber 2000). Measurements were done on a dissecting microscope with an ocular grid and are in mm unless noted otherwise. Photos were made with a Nikon Coolpix 995 digital camera (2048 × 1536 pixels) mounted on a Nikon SMZ 18 stereo microscope or a Leitz Dialux 20 compound microscope. CombineZP (https://combinezp.software.informer.com/) was used for stacking photos. Drawings are partly based on photos that were traced on a light table and later improved under a dissecting microscope, or they were directly drawn with a Leitz Dialux 20 compound microscope using a drawing tube. Cleared epigyna were stained with chlorazol black. Abbreviations used in figures only are explained in the figure legends. Abbreviations used in the text: ALS = anterior lateral spinneret(s); a.s.l. = above sea level; L/d = length/diameter.

DNA sequencing of the CO1 gene was conducted on all three Belisana specimens collected from the Pilbara, Western Australia. Our effort to extract DNA from Buitinga specimens failed. Legs were dissected off the animals for DNA extractions using a Qiagen DNeasy Blood & Tissue kit (https://www.qiagen.com/ie). Elute volumes varied from 40 µl to 200 µl depending on condition and quantity of material. Primer combinations used for PCR amplifications were LCO1490:HCOoutout (Folmer et al. 1994; Schwendinger and Giribet 2005). Dual-direction, Sanger sequencing was undertaken for PCR products by the Australian Genome Research Facility (AGRF). The sequences were edited and aligned in Geneious (Kearse et al. 2012). The three newly sequenced barcodes of Belisana coblynau together with the CO1 barcodes of 19 Belisana species taken from Eberle et al. (2018) were translated into protein sequences using BioPython (version 1.78) (Cock et al. 2009) with invertebrate mitochondrial genetic code. Next, protein-MSAs were constructed using the mafft-linsi algorithm of MAFFT (version 7.487) (Katoh and Standley 2013), which then assisted the construction of nucleotide level MSAs with pal2nal.pl (Suyama et al. 2006). This helps avoid the introduction of biologically meaningless frameshifts to the alignments (Suyama et al. 2006). The genetic distances between different specimens were calculated based on the Kimura 2-parameter (K2P) model (Kimura 1980) using MEGA11 (Tamura et al. 2021), in which ambiguous positions for each sequence pair were deleted. An initial effort to combine the Belisana coblynau sequences with all CO1 Pholcinae sequences from Eberle et al. (2018) and to calculate maximum-likelihood trees was abandoned. The preliminary results from untrimmed and trimmed datasets were highly inconsistent and the suggested affinities not credible (e.g., Belisana coblynau nested in the New World endemic genus Metagonia Simon, 1893).

The taxonomic assignments of the new species to the genera Belisana Thorell, 1898 and Buitinga Huber, 2003 are not immediately obvious and need some justification, especially since this affects the biogeographic interpretation. Both species are clearly representatives of Pholcinae, based on the proximal lateral processes on the male chelicerae. Within Pholcinae, they are very likely representatives of what has been called Pholcinae ‘group 1’ or ‘group 2’ (Huber et al. 2018), i.e. Pholcinae without a distinct sclerite connecting the male genital bulb to the tarsus. These two groups together currently count 16 genera.

For the new Australian species, numerous genera of Pholcinae ‘group 1’ and ‘group 2’ can be ruled out easily: several have only two spigots on each ALS (Aetana Huber, 2005; Hantu Huber, 2016; Khorata Huber, 2005; Paramicromerys Millot, 1946; Savarna Huber, 2005; Spermophorides Wunderlich, 1992; Wanniyala Huber & Benjamin, 2005); in some genera, the genital bulb has only one process, the embolus (Anansus Huber, 2007; Giloloa Huber, 2019; Metagonia Simon, 1893; Nyikoa Huber, 2007; Tangguoa Yao & Li, 2021); females of Spermophora Hentz, 1841 have one or two copulatory pockets behind the epigynum; in Buitinga, males have frontal cheliceral apophyses with modified hairs and females have an epigynal scape; and in Zatavua Huber, 2003 males, the lateral cheliceral apophyses point backwards and there is a retrolateral notch on the palpal tarsus. This leaves only Belisana, which is, together with Spermophora, the only member of Pholcinae ‘group 1’ and ‘group 2’ known to occur in Australia. However, no known species of Belisana has a procursus that has a specific similarity with the procursus of Belisana coblynau Huber & Clark. The large genetic distances to all other sequenced Belisana species (and to other Pholcinae) support the isolated position of this species. Clearly, more molecular data are needed to support or refute our generic assignment. However, the main conclusion is unaffected by the exact generic placement: Belisana coblynau is a relict species. Except for Belisana coblynau, all extant Australian Pholcinae are restricted to the tropical north and east of the continent (Huber 2001, maps 15–19). Certain Pholcinae taxa must have been present in Australia before the climate became drier and more seasonal between 25 and 10 Ma (Martin 1994), or at least before severe aridity set in during the Pliocene (5–2 Ma) (Bowler 1982; Crisp et al. 2004).

Belisana coblynau is the fourth troglomorphic representative of the genus; the three other species are from Thailand, Laos, and Vietnam (Huber 2018). Compared to a sample of 146 described and undescribed congeners (B.A. Huber, unpublished data), B. coblynau is close to the mean values regarding carapace width, tibia 1 length, and metatarsus 1 length. With respect to body size and leg length, the species is thus apparently not troglomorphic.

For the new species from Réunion, most of the possible genera can also be ruled out easily. The following is a selection of diagnostic characters: in numerous genera, frontal male cheliceral apophyses are either absent or they have no modified hairs (Aetana, Anansus, Belisana, Giloloa, Hantu, Khorata, Nyikoa, Savarna, Tangguoa); in some genera, females consistently have epigynal or abdominal copulatory pockets (Anansus, Belisana, Nyikoa, Paramicromerys, Spermophorides, Spermophora, Zatavua); in some genera, the ALS have numerous (5–6) spigots rather than only two (Anansus, Nyikoa, Zatavua); in some genera, the genital bulb has only one process, the embolus (Anansus, Giloloa, Metagonia, Nyikoa, Tangguoa); all known representatives of Wanniyala have a modified male clypeus and long and widely spaced frontal cheliceral apophyses. This leaves only Buitinga (incl. its sister group, a clade of misplaced East African “Spermophora”; Huber et al. 2018), an East African genus in which males of most species have cheliceral apophyses that are very similar to those of the newly described species and in which females are characterized by a scape (even though the shape of the scape in Buitinga ifrit Huber & Cazanove is unique). Surprisingly, however, no known Buitinga in East Africa has a procursus that has a specific similarity with the unique procursus of Buitinga ifrit. If our generic assignment is correct, then the ancestor of Buitinga ifrit must have reached Réunion from East Africa within the last few million years. This is remarkable for two reasons: first, Pholcidae do not easily reach Far Islands (Huber and Meng 2023); second, Buitinga is not known to occur on Madagascar. Buitinga ifrit is the only known troglomorphic representative in the genus.

According to White (1988), a cave can be defined as “a natural opening in the Earth, large enough to admit a human being, and which some human beings choose to call a cave”. The Pilbara (and Yilgarn) troglofauna is unique in that it inhabits a landscape devoid of caves that would fit White’s definition (Halse 2018a, b). Instead, these animals occupy faults, fractures, and voids that form micro-caverns (<5 mm width) and meso-caverns (5–500 mm), which are widespread throughout the landscape (Howarth 1983). These subterranean spaces occur in the host rock of the vadose zone, defined as the space between ~2 m below the ground surface and the water table (Halse and Pearson 2014). The main mechanism resulting in these subterranean spaces is weathering. It is caused largely by water flow, temperature change and animal movement. The related mineralization process whereby minerals are leached from some areas of host rock to enrich other areas can also create voids (Morris 1983). Due to the extreme age of the Pilbara (ca. 3,660–2,800 Ma; Wellman 2000), there are extensive areas within rock formations where subterranean spaces appropriate for subterranean fauna have developed (Johnson 2009).

The Hamersley Range is one of the most prominent features in the Pilbara landscape, and consists largely of exposed banded iron formation (Fig. 5A), a geology known to have been extensively weathered and to contain suitable habitat for troglofauna (Johnson and Wright 2001). These environments have a stable temperature and constant humidity (Moldovan et al. 2018), in contrast to surface conditions where high temperatures and dry conditions are commonplace. It has been suggested that the troglofauna of this region has been forced into the subterranean world by the aridification of the Australian continent (Humphreys 2000; Harvey et al. 2008). Early in the Cenozoic, water was plentiful throughout Australia, but over the course of ~60 Ma, the majority of inland surface water has been lost, with accelerating aridification in the last 33 Ma (Mabbutt 1977; Crisp et al. 2004; Owen et al. 2017). The absence of light and the minimal availability of organic matter (Moldovan et al. 2018) has led to the usual adaptations seen in cave animals: deficient pigmentation, reduced or absent eyes, vermiform bodies, elongate sensory structures, loss of wings, increased lifespan, K-selected breeding strategies, and decreased metabolic rates (Gibert and Deharveng 2002).

Troglofaunal spiders of the Pilbara are estimated to have ranges of between 1 and ~1,400 km² (Halse and Pearson 2014) with a median linear range of 2.2 km (Halse 2018b). For comparison, troglofaunal isopods are understood to have a median range of 1.8 km while dipterans and hemipterans have greater median ranges of 68 and 159 km, respectively (Halse 2018b). The vast majority of troglofauna species have small ranges (< 10,000 km²) and meet Harvey’s (2002) criteria of Short-Range Endemism (SRE).

The Pilbara is one of the richest regions of the world for troglofauna, with over 1,500 species estimated as of 2018 (Halse 2018b). Approximately 7% of collected species from the Pilbara are spiders (Halse 2018b). At least 91 species of spiders are represented within the troglofauna of the Pilbara including the newly discovered pholcid (Bennelongia Environmental Consultants, unpublished data). Of these, the goblin spiders of the family Oonopidae are the most represented in both number of genera (6), number of species (50) and number of specimens (139). All of the described species of troglofaunal spiders of the Pilbara are goblin spiders, with eight species of Prethopalpus described by Baehr et al. (2012). Additionally, the goblin spider Opopaea ectognophus was described by Harvey and Edward (2007) along with two other species from the Cape Range and Kimberley regions of Australia, respectively. An additional goblin spider, Pelicinus saaristoi has been described by Ott and Harvey (2008) from Barrow Island, a subterranean fauna hotspot located off the Pilbara coast (Clark et al. 2021; Eberhard and Howarth 2021). Apart from these few studies, troglofaunal spiders of the Pilbara remain understudied and underrepresented in the scientific literature. Unpublished data suggest the presence of a rich spider fauna, including Gnaphosidae, Linyphiidae, Micropholcommatidae, Symphytognathidae, Tetrablemmidae, Theridiidae, and Trochanteriidae (Bennelongia Environmental Consultants, unpublished data).

Réunion is a volcanic island and its underground environment is largely limited to lava tubes dating back to approximately 300,000 years (Sendra et al. 2017). Several large lava tubes at low altitudes are documented in Audra (1997). The Grotte de La Tortue volcanic tube is located on the northwestern side of the island, at the western base of the now inactive Piton des Neiges volcano. The cave is a lava tunnel system developed within vesicular basaltic lava. The ground hosting this cavity comes from the flows of phase II of the Piton des Neiges (estimated age between 2,100,000 and 430,000 years ago; Brial 1996). It is one of the oldest known caves on Réunion Island. With a maximum length of 322 meters, the cavern system is complex, with many branches and narrow sections (see topographic map in Hoch et al. 2003). The cumulative length of the galleries explored to date is approximately 690 m (Brial 1996). The main entrance is steep and accessible only by ladder or abseil; a second entrance is accessible only by crawling in the Gallery of the Toad. The first cavern forms a large chamber but quickly grades into narrow, shallow passages. At the main entrance, fallen blocks of basalt cover the ground but starting at approximately 2 m from the entrance, these are covered by very fine sediment (50–150 cm thick). This sediment is continuous through the cave system. The cave atmosphere is extremely humid (>97% according to Hoch et al. 2003). The temperature is 25–26 °C (Guillermet 1996; Cazanove and Mahé 2007). Some of the cave floor deposits show evidence of high-energy fluvial activity (ripple marks on shallow compact sediments). Brial (1996) speculated that a lake may form during heavy rains. According to Hume (2005), the cave was a natural pitfall trap for a number of endemic species because several animal bones were found, such as the famous Bourbon Giant Turtle, Cylindraspis indica (Schneider, 1783) and flightless birds (Mourer-Chauviré et al. 1999).

Despite a few studies (Rochat et al. 2003; Cazanove and Mahé 2007), the subterranean fauna on Réunion Island is still poorly known. Previously, only one troglobitic spider species has been known from the island: Trogloctenus briali Ledoux, 2004 (Ctenidae) (Rochat et al. 2003; Ledoux 2004), which is known from a single female specimen collected in Grotte de La Tortue. Other troglobites documented from Réunion include a planthopper (Hoch et al. 2003), Staphylinidae and Carabidae beetles (Jarrige 1957; Deuve 2007; Poussereau et al. 2011; Lecoq 2012) and a diplurid (Sendra et al. 2017). Unpublished records for the Grotte de La Tortue include unidentified representatives of Pseudoscorpiones, Acari, Myriapoda, Coleoptera, Blattoptera (Cazanove and Mahe 2007; G. Cazanove, unpubl. data), as well as two introduced spider species: Eidmanella pallida (Emerton, 1914) (Nesticidae) and Loxosceles rufescens (Dufour, 1820) (Sicariidae) (J.C. Ledoux, pers. comm. 2013).