(Figs 1–15)
Diagnosis. Macropterous. Ocelli present. Antenna filiform, longer than body, antennae 20-segmented at least, flagellum bearing setae, with secondary annulation. Postclypeus gibbous; mx2 with a conical sensillum, mx4 distally broadened and with flat apex; lacinia developed, with three apical teeth; labial palps with two segments, terminal segment rounded. Wings transparent with complete venation. Forewing margin almost glabrous; veins with one row of setae; pterostigma with four sides, but nearly triangular; R 1 twice the length of Sc’. Hindwing with a quadrangular basiradial cell and bifurcate A. Female: Genitalia strongly sclerotized; epiproct subtriangular with round apex; paraproct with 7–8 trichobothria.
Description of holotype female. CAU-BA-LFY-21001 (Figs 1–8). Body length 1.56 mm (measured from frons to terminalia). IO: 0.21 mm, d: 0.15 mm, IO/d = 1.4. f1: 0.13 mm, f2: 0.15 mm, f3: 0.1 mm. FWL: 1.56 mm, FWW: 0.63 mm; HWL: 1.19 mm, HWW: 0.32 mm. ft1: 0.13 mm, ft2: 0.04 mm, ft3: 0.05 mm; mt1: 0.15 mm, mt2: 0.05 mm, mt3: 0.05 mm; ht1: 0.24 mm, ht2: 0.04 mm, ht3: 0.05 mm.
Head with frontal and epicranial suture; compound eyes well developed; three ocelli disposed in triangle between compound eyes. Antennae 20-segmented at least, flagellum bearing setae, with secondary annulation. Maxillary palps four-segmented, mx2 as long as mx4 (Figs 4–5), mx2 with a conical sensillum (Fig. 6). Labial palps two-segmented, terminal segment rounded. Lacinia not visible. Cervical region distinct. Prothorax narrow and short, meso- and metathorax robust.
Wings transparent, venation well developed, but asymmetric (Fig. 3). Forewing with a row of setae on veins, hindwing without setae. Forewing Sc weak and short, ending free in the membrane; pterostigma not thickened, with four sides but similar to triangle; R 1 twice the length of Sc’; Cu2 and A meeting on wing margin; in-flight wingcoupling structure simple, composed of separate and almost straight spines; areola postica narrow and elongate; Cu 1b much shorter than Cu 1a; A simple. Hindwing with Sc reduced; basiradial cell quadrangular; Rs and M with two branches, M fork much longer than Rs fork.
Legs. Tibiae with two distal spurs. Tarsus three segmented. Claws with one preapical tooth.
Abdomen broken, intersegment not visible. Genitalia visible (Figs 7–8). Clunium simple. Epiproct subtriangular with round apex; paraproct with trichobothrial field. Subgenital plate (Fig. 7) simple. External valve visible, sclerotized and bearing setae.
Description of paratype, gender uncertain. CAU-BA-LFY-21002 (Figs 9–15). f1: 0.10 mm, f2: 0.08 mm, f3: 0.1 mm. FWL: 1.39 mm, FWW: 0.5 mm; HWL: 1.09 mm, HWW: 0.38 mm. ft1: 0.15 mm, ft2: 0.04 mm, ft3: 0.05 mm; mt1: 0.15 mm, mt2: 0.20 mm, mt3 broken; hind leg tarsi missing.
Body and wings similar to the CAU-BA-LFY-21001, but dehydrated and broken. Lacinia (Figs 10, 15) with three apical teeth. Labial palps (Figs 10, 14) with rounded apex. Wings with “normal” venation, left and right venation symmetric. Forewing (Fig. 11) Rs with two branches, M with three branches, in-flight wing-coupling structure simple (Fig. 13). Hindwing (Fig. 12) with M fork not much longer than Rs fork. Abdomen terminal with a sacshaped structure.
Type materials. The type specimens will eventually be deposited in the Entomological Museum, China Agricultural University (CAU). Holotype: CAU-BA-LFY-21001, female. Paratype: CAU-BA-LFY-21002, gender uncertain.
Etymology. The new species is dedicated to Prof. Ding Yang for his support to the study of Chinese Psocodea.
Remarks. Wang et al. (2019) and Hakim et al. (2020) indicated the venation of Psocodea is variable. The holotype of the new species shows asymmetric venation: left forewing with Rs two-branched; M three-branched, but M3 branched; right forewing with Rs bifurcating into R 2+3 and R 4+5, but R 4+5 branched; M three-branched, but the middle branch not reaching wing margin.
This new species can be included in Psyllipsocus by the following characters: 1) lacinia with three apical teeth; 2) forewing Sc short and ending free in membrane; 3) forewing veins with one row of setae; 4) forewing pterostigma with four sides; 5) Cu2 and A meeting at forewing margin, in-flight wing-coupling structure composed of separate and almost straight spines; 6) broad and pilous external valve.
Psyllipsocus yangi differs from the genera Concavapsocus Wang et al., 2019 and Khatangia Vishniakova, 1975 by the presence of nodulus; differs from the genus Libanopsyllipsocus Azar & Nel, 2011 by the presence of pterostigma; and differs from the genus Annulipsyllipsocus Hakim et al., 2018 by the pterostigma with four sides. This new species is similar to Sinopsyllipsocus fushunensis in the subtriangular pterostigma, the annulated flagellomeres and the presence of a conical sensillum in mx2, but it differs from this taxon by the shorter forewing, the completely transparent wings, the quadrangular basiradial cell and bifurcated A in hindwing.
Zhang et al. (2016) established the genus Sinopsyllipsocus based on S. fushunensis from Fushun amber (early Eocene), and placed this genus into the family Psyllipsocidae because of the forewing venation, and distinguished Sinopsyllipsocus from the other genera of Psyllipsocidae by the presence of secondary annulation on the antennae and the presence of a sensillum on mx2.
Secondary annulation in the antennal flagellomeres is considered an apomorphy for the suborder Troctomorpha (Lienhard 1998), although Hakim et al. (2018) and Perrichot et al. (2003) suggested that this character could be homoplastic.
Yoshizawa et al. (2006) reconstructed the phylogenetic relationships among extant families of the suborder Trogiomorpha based on molecular data, and considered “mx2 without conical sensillum” is a key diagnostic character of Psyllipsocidae. However, Lienhard and Ferreira (2013, 2014) described nine species of Psyllipsocus with a conical sensillum on mx 2 in Brazilian caves, contradicting the diagnosis of Psyllipsocidae of Yoshizawa (2006).
In view of the above, Sinopsyllipsocus is very similar to Psyllipsocus, and it is possible that Sinopsyllipsocus and Psyllipsocus constitue a single lineage.