OPISTHOTHELAE Pocock, 1892

Downen, Matthew R. & Selden, Paul A., 2020, Fossil spiders (Araneae) from the Eocene Kishenehn Formation of Montana, USA, Palaeontologia Electronica (a 56) 23 (3), pp. 1-10 : 3-4

Suborder OPISTHOTHELAE Pocock, 1892 Infraorder ARANEOMORPHAE Smith, 1902 Araneomorphae incertae sedis

( Figure 1 )

Remarks. Parts of this fossil spider are preserved with high fidelity (the legs), whereas other portions are poor in detail (the palps and carapace). The palps, carapace, and some of the leg joints have been replaced with pyrite which contributes to a loss of detail. Mygalomorph spiders typically have large porrect chelicerae and robust legs. The fossil here has relatively small chelicerae that are not porrect, and legs that are relatively slender with heavy spination. The pedipalps are modified, indicating the specimen is an adult male. A large cymbium is observable on each palp, as well as a median apophysis and other structures of the palpal bulb, suggesting it is relatively complex like most araneomorph spiders. Most of the femora are distorted (likely due to compression) and are likely longer than they appear. The third leg of the spider is the shortest, but it is not quite as short as most orbweaving spiders. Tarsus IV possesses fine setae, but no tarsal comb is visible, as is in the family Theridiidae . Two tarsal claws can be made out on some legs, and there do not appear to be any dense claw tufts or scopulae, so the specimen is unlikely to belong to Clubionidae or Corinnidae .

Description of PAL 583.1. Male Carapace rounded, longer than wide (L 0.62, W 0.48). Abdomen about as long as wide (L 0.76, W 0.78), with circular darkened area at anterior extending to almost full length of abdomen. Spinnerets small and conical, at posterior most tip of abdomen (abdomen does not overhang spinnerets). Cymbium oval, almost half the length of the carapace, covered in fine setae. Hook-shaped median apophysis. Walking leg formula I>II>IV>III. Legs spinose and covered in fine setae and erect long and thick spine-like macrosetae. Single spine-like macrosetae on each patella, two on proximal tibia of all legs. Shorter macrosetae on metatarsus.

Figures

FIGURE 1. Specimen PAL 583.1 Araneomorphae incertae sedis photograph and interpretive drawing.