A new monotypic genus in the orb-weaving spider family Araneidae Clerck, 1757 is described from Australia: Abba gen. nov., with Abba transversa (Rainbow, 1912) comb. nov. as the type species. It differs from all other genera in the family by somatic characters, specifically a patch of approximately five long spines on the prolateral surface of the first leg in males and an abdominal colouration with a pair of two central spots dorsally on a creamy-white surface. Specimens of A. transversa comb. nov. have been collected in Queensland and New South Wales, where the species is largely summer-mature. We also provide a genus level summary of all Australian Araneidae, currently consisting of 230 described species and eight subspecies in 46 genera.

Taxonomy, systematics, monotypy, araneids

There are currently 230 described species and eight subspecies in 46 genera of araneid orb-weaving spiders known from Australia (Table 1). The genus Araneus Clerck, 1757 is the most speciose of these and includes almost double the number of species as each of the second-largest genera, Argiope Audouin, 1826 and Dolophones Walckenaer, 1837 (Table 1). However, Araneus (or its junior synonym Epeira Walckenaer, 1805) was used by early arachnologists as a dumping ground for species that could not be placed in other genera, and a detailed examination of all available Australian type material of araneids over the last 15 years showed that true Araneus species do not occur in Australia (VWF unpublished data). It is clear that substantial taxonomic work is needed to transfer current Australian Araneus species into appropriate genera with most of them yet to be described (see Framenau 2019). This has recently been completed for many genera of the informally termed ‘backobourkiines’ sensu Scharff et al. (2020) (e.g., Framenau and Kuntner 2022; Framenau et al. 2022a and references therein).

Australian araneid genera are generally species-poor, and Cyrtobill Framenau & Scharff, 2009, Lariniophora Framenau, 2011, and Quokkaraneus Castanheira & Framenau, 2022 are monotypic (Table 1). Arguably, this list should also include Austracantha Dahl, 1914, with its four current subspecies likely synonyms of the nominal species, as well as the enigmatic Paraplectanoides Keyserling, 1886, where the second species in the genus, P. kochi (O. Pickard-Cambridge, 1877), is more likely a member of the Arkyidae L. Koch, 1872 based on its original description.

Araneus transversus Rainbow, 1912 was described based on a male and female collected in the Blackall Range north of Brisbane in south-eastern Queensland (Rainbow 1912). However, the validity of this species remained controversial, specifically as Davies and Gallon (1986) cryptically synonymized the species with Gea theridioides (L. Koch, 1872) based on the syntype female, a synonymy currently not accepted in the World Spider Catalog (2022). Indeed, the male syntype has an unusual morphology for an araneid, with long spines on the first pair of legs and a distinct abdominal colouration.

Comprehensive examinations of Australian collections and key overseas institutions holding Australian spider material did not reveal any species that could be considered congeneric to the male syntype of Araneus transversus based on morphological characters. This species also does not display any of the synapomorphies of araneid genera currently described from Australia. Therefore, a new monotypic genus is here proposed to accommodate A. transversus as a phylogenetic hypothesis within the context of other genera pending further studies into the Australian Araneidae.

This study is part of a comprehensive 15-year study on Australian Araneidae based on material in all major Australian museums and overseas collections where historical type material is lodged, totalling almost 12,000 records (vials).

Descriptions and terminology follow recent publications on Australian orb-weaving spiders (e.g., Framenau and Castanheira 2022c; Framenau and Kuntner 2022; Framenau et al. 2022a). We separated the characters for the genus- and species-level descriptions as done previously for Courtaraneus Framenau, Vink, McQuillan & Simpson, 2022, Lariniophora and Quokkaraneus Castanheira & Framenau, 2022 (Framenau 2011b; Castanheira and Framenau 2022; Framenau et al. 2022b), i.e., genus-level characters described here are those shown to be informative at that level by a previous morphological systematic study on the Araneidae (Scharff and Coddington 1997). The descriptions are based on recently collected specimens as the male syntype is in poor condition. Colour patterns are described based on specimens preserved in ca. 75% ethanol. The male pedipalp was expanded by alternatively submerging it for around 10 min in 10% KOH and distilled water until fully expanded. The epigyne was cleared in 10% KOH and examined embedded in lactic acid on a microscopic slide under a cover glass.

Microscope photographs were taken with two different stereo-imaging systems. At the Natural History Museum, Copenhagen (Denmark), images were taken with a Nikon D300 digital SLR camera attached via a C-mount adapter to a Leica M16A stereomicroscope. Images of different focal plains were stacked with Automontage (v. 5.02) software from Syncroscopy to increase the depth of field. At the Harry Butler Institute, Murdoch University (Australia), images were taken in different focal planes with a Leica DMC4500 digital camera mounted to a Leica M205C stereomicroscope and combined using the Leica Application Suite X, v. 3.6.0.20104. All photos were edited with Photoshop CC 2020.

All measurements are given in millimetres. They were taken with an accuracy of 0.1 mm, except for eye and labium measurements taken with an accuracy of 0.01 mm.

Maps were compiled in the software package QGis v. 3.2.6 (https://qgis.org/en/site/; accessed 14 November 2022). Geographic coordinates were extracted directly from the original labels or the registration data as provided by the museums. When no detailed geographic information was available, localities were estimated based on Google Earth v. 9.1.39.3 (https://earth.google.com/web/ accessed 14 November 2022) to the closest minute of Latitude and Longitude.

The erection of a monotypic genus for one of the many Australian species currently listed in Araneus is not taken lightly and follows extensive examinations of all available material in Australian collections over more than 15 years. Platnick (1976) and Wiley (1977) provide a philosophical discussion on monotypy, but irrespective of their opposing views, monotypic genera representing species not displaying synapomorphies of other taxa are not uncommon in spiders, including the Araneidae (Table 1). It is clear that Abba transversa comb. nov. does not share the synapomorphies of any currently described Australian genera. Its highly derived autapomorphies, the prolateral spines on the first leg of males and the unusual abdominal colouration, justify the erection of a new genus for this species and will improve its diagnosability in future keys of Australian araneids.

Abba transversa comb. nov. was not included in any of the recent, large-scale molecular phylogenetic analyses of the Araneidae (e.g., Kallal and Hormiga 2018; Scharff et al. 2020), and its systematic placement based on morphology within an Australian context is difficult. It does not share the putative synapomorphies of the backobourkiines, i.e., a single macroseta on the pedipalp patella of males and the median apophysis forming an arch of the radix (see Scharff et al. 2020) and is therefore unlikely part of this diverse and dominant Australian clade. The species is more likely associated with Scharff et al.’s (2020) well supported zealaraneines. Although this clade has currently no known morphological synapomorphies, most species, like A. transversa comb. nov., have two patellar spines on the pedipalp and the epigyne has a terminal pocket (see Court and Forster 1988). Scharff et al. (2020) identified other Australian species to be part of the zealaraneines, i.e., Araneus albotriangulus (Keyserling, 1887) and Ar. talipedatus (Keyserling, 1887), but both are very unlike Ab. transversa comb. nob. and deserve placement in their own new respective genera (“NGEN08” and “NGEN06” in Scharff et al. 2020, respectively).

The presence of a patch of long macrosetae on the prolateral surface of the first pair of legs in males represents one of the diagnostic characters of Abba gen. nov. Strong macrosetae on the first legs of spiders are not uncommon and occur, for example, in Arkyidae, Mimetidae Simon, 1881 and Thomisidae Sundevall, 1833 (e.g., Harms and Harvey 2009; Framenau et al. 2010a; Machado et al. 2019). However, in those families, they are present in both males and females and likely support retaining prey in these sit-and-wait predators. By contrast, in Abba gen. nov., the spines on the first legs only occur in males and are therefore more likely a result of sexual selection. Unfortunately, nothing is known about the behaviour of these spiders, and it is unclear if the unusual macrosetae are used in male-male competition for mates or have a role during courtship behaviour. Sexually selected modifications of legs are very common in male orb-weaving spiders but more often relate to the second pair of legs (Framenau et al. 2021a). In many genera, including those in the Australian backobourkiines, the tibia of the second pair of legs in males is much more robust than the others and has enforced spines and spurs (e.g., Scharff and Coddington 1997; figs 1–2). In these cases, the enlarged second tibia is used to fend off females during courtship (Framenau et al. 2021a, pers. comm.).

We thank Robert Raven (retired) and Owen Seeman (both QM), Graham Milledge (retired) and Helen Smith (both AM), and Mark Harvey and Julianne Waldock (both WAM), for the loan of specimens in their care or assistance when visiting their respective institutions. Nikolaj Scharff hosted both authors at a number of occasions in Copenhagen and shared great insights into araneid phylogeny and systematics. Agnetha Fältskog, Björn Ulvaeus, Benny Andersson, and Anni-Frid Lyngstad are thanked for the many hours of musical entertainment.

We acknowledge the support of the Leibnitz Institute for the Analysis of Biodiversity Change (LIB), University of Hamburg on waiving the processing fee of this manuscript and thank Danilo Harms (editor), and the two reviewers (Robert Raven and Sarah Crews) for their valuable comments that considerably improved the quality of our manuscript.

Funding for revisions of the Australian Araneidae was provided by the Australian Biological Resources Study (ABRS) (grant no. 205-24 [2005–2008] to VWF and N. Scharff and grant number 4-EHPVRMK [2021–2023] to VWF, PSC, N. Scharff, D. Dimitrov, A. Chopra and R. Baptista).