Arthrolycosa wolterbeeki, Dunlop1, 2023

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

Arthrolycosa wolterbeeki sp. nov.

Holotype. MB.A. 4298 (ex. TKTW0711A/B ), part and counterpart.

Type locality. From the Piesberg quarry near Wallenhorst, Lower Saxony, Germany.

Age of the type locality. Part of the Osnabrück Formation, late Carboniferous (Moscovian); or Westphalian D in the regional stratigraphy.

Zoobank LSID. 722E7CF1-D026-49EC-91BB-BD28E- C5E36E4.

Diagnosis. Arthrolycosa with a relatively compact body, opisthosoma somewhat rounded, nearly as wide as long, thus not noticeably longer than wide and suboval as inferred for A. antiqua . Tuberculation along posterior margins of opisthosoma more prominent than in A. antiqua . Pedipalp rather long, at least 1/2 the length of the adjacent legs; ca. 1/3 the length in A. antiqua .

Etymology. In honour of Dr Tim Wolterbeek, who discovered the holotype and kindly made it available for study.

Description

Almost complete specimen in both dorsal and ventral view. Total preserved length ca. 7.7, but front of carapace missing. Maximum width of carapace 4.8; posterior margin straight to slightly procurved and whole carapace apparently rebordered at least laterally and posteriorly. Anterior region (including any eyes and/or eye tubercles) equivocal, but with a distinct depression (fovea), on the midline and a pair of shallow sulci behind it. Two rectangular to quadratic structures on ventral surface (length 1.2) may be displaced chelicerae, one with evidence for a row of up to five denticles. Coxo-sternal region generally not well preserved. Several subtriangular elements hint at leg coxae, but details largely equivocal.

Pedipalps pediform, long, total length ca. 9.0; lengths of individual articles hard to resolve but femur ca. 3.6, and tarsus at least 2.6. Tarsus ends in a single terminal claw with no evidence for a modified (male) palpal organ. Legs robust and relatively elongate compared to body; femur, patella and tibia quite broad, metatarsus and tarsus more slender; at least leg I terminating in one of a pair(?) of robust claws, but no evidence for an empodium. Right leg 1 largely absent. Left leg I complete, total length ca. 13.4; article lengths: femur ca. 3.7, patella 1.6, tibia 3.6, metatarsus 2.9, tarsus 1.6. Leg II almost complete, total preserved length ca. 11.5; article lengths: femur ca. 3.0, patella 1.6, tibia 4.0, metatarsus 2.9; tarsus missing. Leg III complete, total length 11.9; article lengths: femur ca. 3.4; patella 1.3, tibia 2.7, metatarsus 2.5, tarsus 2.1. Leg IV incomplete, total preserved length ca.13.3; article lengths: femur 4.8, patella 1.4, tibia 5.2; metatarsus incomplete and tarsus missing. Leg formula thus probably IV> I> II> III. Pedipalps and legs with relatively dense setation towards the distal ends, from the tibia onwards, and especially on underside of metatarsus and tarsus of legs.

Opisthosoma compact, oval to shield-shaped in outline with maximum length and width of 5.2. At least eight tergites visible dorsally, all with more or less straight margins, with maximum lengths of ca. 0.9, but shorter towards the posterior end. Five posteriormost tergites each with a row of up to six small tubercles (diameters ca. 0.15), closer to posterior margin. Anterior three tergites show no evidence for tuberculation. Ventrally at least six sternites visible, again with straight margins and lengths up to ca. 0.9, and with shorter sclerites posteriorly. Postanal telson absent; but small posterior element shaped like an inverted triangle could be the anal tubercle. No ventral tuberculation was preserved, but possible diamond-shaped element is present on ventral midline in about the position where the genital opening would be expected ( Fig. 2a ). Two slender elements (displaced spinnerets), length ca. 2.2, width 0.2, preserved to the left of dorsal opisthosoma with slight curvature. At least one appears articulated, with evidence for up to eight individual elements ( Fig. 3c ). In ventral view, possibly originating from a rectangular (basal?) element, which would give entire structure a length of ca. 3.7. Less well-defined feature on opposing side of opisthosoma could represent one of a further pair of long spinnerets, but preservation is poor rendering its interpretation equivocal.

Figures

Fig. 2 Interpretative camera

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