Arthrolycosidae Harger, 1874

Dunlop 1, Jason A., 2023, The first Palaeozoic spider (Arachnida: Araneae) from Germany, PalZ 2023, pp. 1-8 : 3

Family Arthrolycosidae Harger, 1874

Taxonomic remarks. Spinnerets are one of the defining characters of spiders; thus, their presence here in the Piesberg fossil ( Fig. 3C ) indicates that it belongs to Araneae and is not part of the assemblage of spider-like fossils, which Selden (2021) designated Tetrapulmonata incertae sedis; whereby the tetrapulmonates include the spiders and their closest relatives such as whip spiders and whip scorpions. The opisthosoma of the new fossil preserves distinct tergites and sternites ( Figs. 1–2 ). This is a plesiomorphic character for spiders, but is consistent with it being a member of the suborder Mesothelae , which retains a segmented opisthosoma.

As noted above, three Carboniferous mesothele families were recognised, and re-diagnosed, by Selden (2021). Arthrolycosidae was characterised as Mesothelae in which the opisthosomal tergites occupy the full width of the opisthosoma and are not set in soft cuticle. By contrast, Palaeothelidae comprise mesotheles where the opisthosomal tergites are distinct, but do not extend across the full width of the opisthosoma and are set in soft cuticle. Arthromygalidae were defined as having tarsi with elongate paired claws and an apical empodium (or pseudopulvillus), slender legs and a carapace nearly as wide as long. Based on these criteria, the new fossil is most consistent with Arthrolycosidae as the tergites appear to occupy the full width of the opisthosoma without any surrounding soft cuticle ( Figs. 1 , 2 ). The carapace proportions characteristic of Arthromygalidae cannot be easily tested against the new fossil as the carapace is missing the anterior margin, but the legs of the Piesberg spider are fairly robust, and the one well-preserved tarsus ( Figs. 1 , 2 ) shows no evidence for an empodium associated with the claws.

Figures

Fig. 3 Details of the specimen shown in Fig. 1. a Setose distal ends of walking legs I and II. b Setae adorning the pedipalp. c Putative spinneret show- ing evidence of segmentation (arrowed). Scale bars equal 1 mm

Fig.1 Arthrolycosa wolterbeeki sp. nov., the oldest fossil spider (Arachnida: Araneae) from Germany, from the late Carboniferous of Piesberg near Osnabruck, Lower Saxony. a Part. b Counterpart. Scale bar equals 5 mm

Fig. 2 Interpretative camera