Scopomegops fax, Guo & Selden & Ren, 2022

Guo, Xiangbo, Selden, Paul A. & Ren, Dong, 2022, New specimens from Mid-Cretaceous Myanmar amber illuminate the phylogenetic placement of Lagonomegopidae (Arachnida: Araneae), Zoological Journal of the Linnean Society 195, pp. 399-416 : 402-404

SCOPOMEGOPS FAX GUO ET AL. sp. nov.

( FIG. 2 )

Zoobank registration: u r n: l s i d: z o o b a n k. org:act: A897B322-B55F-4652-AF1C-FAD42209F78C

Etymology: The specific name is the Latin noun fax , meaning torch, referring to the shape of the male palp.

Holotype: Male, specimen no. CNU-ARA-MA2020001.

Locality and horizon: Hukawng Valley, Kachin State, northern Myanmar; lowermost Cenomanian, Mid-Cretaceous.

Diagnosis: As for the genus.

Taphonomic features: CNU-ARA-MA2020001: femur, patella, tibia, metatarsus, tarsus of left leg II and metatarsus, tarsus of right leg I are missing; left leg I, caused by developmental malformation or autotomy, is much smaller than right leg I; the abdomen is compressed; there is a large bubble on the left side of the abdomen, and several small bubbles around the spider. A thrips near the left leg IV is present as a syninclusion.

Description: Body length 4.97, carapace light-coloured medially, dark-coloured laterally, a pair of indistinct dark longitudinal stripes on abdomen dorsally. Carapace piriform in outline, length 2.44, width 1.54 at widest point, covered with short, dense, feathery setae pressed flat against the cuticle. Cephalic region of carapace slightly raised, with a pair of distinct protrusions beneath the inner side of PME ( Fig. 2G ). Fovea oval, shallow, situated in the centre of carapace, next to the posterior margin of cephalic region. Eight eyes present; PME enormous, 0.43 in diameter, situated on anterolateral corner of carapace; PLE small, placed at the mediolateral margin of cephalic region, separated 0.50 from the PME centre; AME and ALE contiguous, situated between the PME and the clypeal margin ( Fig. 2G ). Chelicera length 0.96, and width 0.36 at base, cheliceral insertion close to mouthparts, stridulatory files absent. Fang length 0.33. Chelicera with about six peg teeth on promargin ( Fig. 2C ); retromargin unrecognizable. Labium ligulate, longer than wide, not fused to sternum. Endites elongated, converging and meeting in midline; apex and prolateral margin of endites brushy with dense setae; serrula as a single row of teeth. Sternum shield shaped, covered with setae, slightly convex and without tubercles.

Palpal podomere lengths: fe 1.01, pa 0.40, ti 0.43, ta 0.98. Palp hairy, feathery setae at least present on tibia. Tibia with at least three dorsal trichobothria in a single row; a small apophysis present on the distal retrolateral surface of tibia, several clustered clavate spicules situated on the top of retrolateral apophysis ( Fig. 2D, H ). Male palp torch-like, cymbium elongate; embolus curved, slightly embraced by the long sheet conductor; median apophysis horn-like; subtegulum round, with a distally curved apophysis ( Fig. 2I–L ; File S4).

Legs long but no legs enlarged; metatarsus distinctly much longer than tarsus in all legs. Leg formula II> I> IV> III: leg I cx 0.64, tr 0.11, fe 2.81, pa 0.92, ti> 2.69; leg II cx 0.60, tr 0.11, fe 2.95, pa 0.84, ti 3.42, mt 2.42, ta 0.87; leg III cx 0.60, tr 0.10, fe 1.94, pa 0.65, ti 1.92, mt 1.13, ta 0.63; leg IV cx 0.65, tr 0.12, fe 2.51, pa 0.77, ti 2.28, mt 2.01, ta 0.82. Metatarsus and tarsus without scopulae. Distal preening comb composed of eight short macrosetae, present on metatarsus of posterior legs ventrally ( Fig. 2E, F ). Feathery setae at least present on all tibia. Tibiae with about 14, metatarsi with about ten, tarsi with about ten trichobothria ( Fig. 2E, F ). Three tarsal claws, paired claws with about four to five teeth, distal two teeth distinctly larger than others, median claw hook-like. Abdomen length 2.17, width> 0.66, densely covered with short setae. Four spinnerets visible, details unrecognizable.

Remarks: Holotype with left leg I much smaller than right leg I. It was caused by developmental malformation or autotomy. Autotomy is a voluntary act allowing most spiders to amputate one of their own legs to escape from a perilous situation. Although the lost legs can be replaced by new ones regenerated after the next moult, these are usually smaller, and need further moults to grow into normal size ( Foelix, 2011).

Figures

Figure 2. Scopomegops fax, holotype CNU-ARA-MA2020001: A, habitus, lateral view; B, schematic drawing of lateral habitus; C, distal part of chelicerae, dorsal view, showing peg teeth; D, tibia and male palp of right pedipalp, dorsal view, showing retrolateral tibial apophysis (arrow); E, tarsus of left leg IV, lateral view, showing trichobothria (asterisks); F, metatarsus of left leg IV, lateral view, showing trichobothria (asterisks) and preening comb (arrow); G, cephalothorax, lateral view, showing eyes and abnormal left leg I; H, tibia of left pedipalp, lateral view, showing trichobothria (asterisks) and retrolateral tibial apophysis (arrow); I, left male palp, retrolateral view; J, left male palp, ventral view; K, 3D CT reconstruction of left male palp, ventral view; L, reconstruction of left male palp, ventral view. Scale bars represent 1 mm (A, B) 0.5 mm (G), 0.2 mm (D, E, F) and 0.1 mm (C, H, I, J, K, L).