Gigarachne bian Jiang & Li 2020, sp. nov.

Gigarachne bian Jiang & Li, sp. nov. (Figs 4–6)

Holotype ♂ (IZCAS-Ar41630Fo), Late Cretaceous amber from Myanmar, Kachin State, Hukawng Valley. Syninclusions include a Neuropteran near the spider’s mouthpart, which is a potential prey of the spider, but not wrapped with silk. In addition, two dipterans and three hymenopterans also occur in the same piece of amber.

Etymology. The specific name is derived from the Chinese pinyin word for “flat” (biǎn), referring to the flattened prosoma and abdomen of the species, and is a noun in apposition.

Diagnosis. Gigarachne bian Jiang & Li, sp. nov. can be distinguished by the characters of the family, as given above.

Description. Male (holotype). Body length 14.42, carapace 5.77 long, 3.24 wide, prosoma 0.97 high, abdomen 8.65 long, 2.03 wide, 0.51 high. Eyes (severely deformed by preservation and thus asymmetric in measurements): left AME 0.23, right AME 0.30, left ALE 0.225, right ALE -, left PME 0.23, right PME 0.30, left PLE -, right PLE -, AME-AME 0.28, AME-ALE 0.24, PME-PME 0.29, PME-PLE -, AME-PME 0.30, ALE-PLE -, CH AME -, CH ALE -. Spination: palp: 1100, 1210, 2111; legs: femur I 144, II 350, III -, IV 012 (incomplete); patella I -, II 2010, III -, IV 1211; tibia I -, II 1012, III -, IV 1211 (incomplete); metatarsus I 1112, II 4442, III 3234, IV 3332; tarsus without spines. Measurements of palp and legs: left side: palp 5.08 (2.00, 0.67, 1.25, 1.16), leg I - (11.09, -, -, -, 5.77), leg II 32.18 (10.83, 1.87, 7.75, 8.11, 3.62), leg III - (6.41, -, -, -, -), leg IV 23.71 (6.53, 1.85, 6.45, 6.75, 2.13); right side: palp - (-, 0.72, -, 1.23), leg I - (-, -, -, -, -), leg II - (-, -, -, -, -), leg III 17.63 (6.44, 1.63, 3.80, 4.04, 1.72), leg IV 23.50 (6.60, 1.88, 6.06, 6.64, 2.32).

Carapace ampullate; prosoma extremely flat (height/length ratio 0.168), covered by hairs and few feathery scales; pars cephalica slightly elevated; fovea distinct, deep and longitudinal (Fig. 5B). Eight eyes, all severely deformed; eye domain strongly protruding, AME and PME on a tubercle with AME situated on apex; ALE and PLE separate, but on common lateral tubercles; both anterior and posterior eye row recurved in dorsal view (Fig. 5D). Chelicerae covered by setae at promargin (Fig. 5E); few true teeth present on promargin and retromargin; fangs long. Endite not converging, tapering, longer than width; serrula in a single row; labium longer than wide, not fused to sternum (Fig. 5E); sternum shield-shaped, longer than wide, extending between coxae IV (Fig. 5B). Legs elongated, leg formula 1243, covered by hair, feathery scales present but not dense; tactile hairs plumose; spines numerous (see above), but absent in all tarsi; spines at apex of metatarsi forming a ring; metatarsal preening combs absent; vestigial calamistrum in male absent; femoral trichobothria absent; ITC present, slightly smaller than STC; STC teeth uniseriate, three or four; serrate accessory claw setae present (Fig. 5C). Abdomen elongated and extremely flattened (height/length ratio 0.059), severely wrinkled by preservation, with scattered black spots and patches, length more than four times width, unsclerotized, covered by many hairs and few feathery scales; one pair of booklungs; clusters of plumose setae present on distal half of dorsal abdomen in one pair; spiracle and spinnerets covered by dark grey cloudy matter and thus not observable; end of abdomen most likely extending beyond invisible spinnerets and anal tubercle, bearing long hairs (Figs 5A–B).

Male palp (Figs 6A–C). Both palps severely deformed, rendering asymmetrical morphology of podomeres and bulbs. Femur longest, bearing spines, without apophysis. Tibia with dorsal spines, without apophysis. Cymbium spoon-shaped, densely covered by long hairs, dorsal spines present, paracymbium absent. Tegulum bearing five apophyses, homology difficult to infer.

Female. Unknown.