A New Genus and Species of the Suborder Trogiomorpha (Insecta, Psocodea) from Mid-Cretaceous Amber of Myanmar

Simple Summary The insect order Psocodea is one of the common groups of the entomofauna from Cretaceous Burmese amber. These fossil species have shown numerous diagnostic characteristics common with the extant psocids. The psocodean suborder Trogiomorpha is considered the sister group of the other psocodean taxon. In this study, we describe a new genus that is tentatively placed into Trogiomorpha and consider it a close relative to the family Cormopsocidae. However, its familial placement is undetermined. This discovery will be a helpful contribution to understanding the ancestral characteristics of Psocodea. Abstract We established a new genus with a new species Brachyantennum spinosum Liang et Liu, gen. et sp. nov. from mid-Cretaceous Burmese Kachin amber. It is tentatively placed into the suborder Trogiomorpha, based on the strong external valve, the reduced dorsal and ventral valve, and the short subgenital plate covering the basal part of the external valve. This new genus is apparently close to the family Cormopsocidae, based on the well-developed and very long hindwing Sc vein. However, its familial placement is ambiguous and it can be excluded from the established families of Trogiomorpha by the presence of the tarsal ctenidiobothria on the mid- and hindleg.


Introduction
The insect order Psocodea, an inconspicuous group, includes parasitic lice, book lice, and bark lice [1,2]. Psocodea is divided into three suborders: Trogiomorpha Roesler, 1944, Trcotomorpha Roesler, 1944, and Psocomorpha Weber, 1936 [3]. The monophyly of all the suborders has been confirmed by morphological and molecular data, and Trogiomorpha is considered as the sister group to Trcotomorpha plus Psocomorpha [4][5][6]. However, the origin of Psocodea and the divergence of these suborders are controversial in different studies because of insufficient fossil data [4,7,8]. Impression fossils of Psocodea before the Cretaceous period are extremely rare, and it is hard to gain enough morphological data from these materials [9]. Therefore, psocids from Cretaceous amber are potentially useful materials that can be used in phylogenetic dating analyses.
In this study, we describe a new genus and species of Trogiomorpha from mid-Cretaceous Burmese Kachin amber. It is close to the family Cormopsocidae, but its familial placement is undetermined.

Materials and Methods
The amber specimen herein studied is from the Hukawng Valley in Tanai Township, Kachin State, northern Myanmar, and it is earliest Cenomanian in age, 98.8 ± 0.62 million years, by U-Pb dating of zircons from the volcanoclastic matrix of the amber [18,19].
Observations were made by using an Olympus CX-33 (Olympus Imaging Corporation, Tokyo, Japan) light microscope. Photographs and drawings were taken by using a Sony Alpha 7II (Sony Corporation, Tokyo, Japan) digital camera attached to the Olympus CX-33. The figures were prepared with Adobe Photoshop 24.0.0 (Adobe, San Jose, CA, USA).

Order
Diagnosis. Macropterous. Ocelli present; antennae very short, with 11 antennomeres, flagellomeres with secondary annulations; lacinia rob-like; mx2 and mx4 without conical sensillum, mx2 longer than mx4. Forewing: base of anterior margin with setae; veins with one row of setae; Sc well developed and forming arched, joining R near base of pterostigma; R 1 curved, without angle; crossvein r-rs present, connecting pterostigma and Rs; ap cell broad, subtriangular; CuP and A ending closely, but not meeting on forewing margin; nodulus absent. Hindwing glabrous, Sc very long and ending on wing margin; A bifurcate, A1 curved. Leg: femora and trochanters without spines; tibiae bearing spines; tarsus three-segmented; 1st tarsus with one row of ctenidiobothria on mid-and hindleg; pretarsal claw symmetrical, with a preapical tooth. Female genitalia strongly sclerotized. Clunium simple, not fused to subgenital plate. Epiproct with short setae. Paraproct with long setae. External valves strong and broad, with several spurs on the margin.
Type material: Holotype, CAU-BA-LFY-21003, female, deposited in the School of Life and Health Science, Hunan University of Science and Technology. The type specimens will eventually be deposited in the Entomological Museum, China Agricultural University (CAU), Beijing, China, after the authors end their careers.
Diagnosis. As for the genus. color pattern; ocelli white. Fore-and hindwing transparent. Abdomen dark brown.
Abdomen. Female genitalia strongly sclerotized. Clunium simple, not fused to subgenital plate. Epiproct with short setae, paraproct with long setae. A pair of strong and broad external valves visible in lateral view, appeared out of subgenital plate, with several spurs on the tip of external valve. Subgenital plate broad and strongly sclerotized.

Discussion
Yoshizawa et al. [21] concluded that the suborder Trogiomorpha can be identified based on three morphological apomorphic features: (1) the reduced ventral and dorsal valves; (2) the well-developed external valve close to the ventral midline of the abdomen; and (3) the short subgenital plate, covering at the basal part of the external valves. Therefore, we placed the new genus Brachyantennum gen. nov. into Trogiomorpha based on these characteristics.
Brachyantennum gen. nov. is similar to the two families Cormopsocidae and Prionoglaridiae in the forewing venation, especially in the well-developed and strongly curved Sc, and the presence of a cross-vein between the pterostigma and Rs. Yoshizawa and Head (Figure 1). Compound eyes ( Figure 1C) and ocelli ( Figure 1D) bulged. Vertical suture visible, frontal suture not visible, epistomal suture distinct. Antenna filiform, with 11 antennomeres; flagellomeres short, with secondary annulations ( Figure 1E). Lacinia ( Figure 1F) simplified, rob-like. Maxillary palps four-segmented, without visible sensillum on any segment, mx2 longer than mx4. Labial palps two-segmented.
Thorax well preserved. Prothorax short. Meso-and metathorax robust. Wings (Figure 2A-D) transparent, with developed venation. Forewing (Figure 2A-C): base of anterior margin ( Figure 2B) with setae; veins with one row of setae; Sc well developed and forming arched, joining R near 2/3 R; R 1 arc, without posterior angle; Rs with two branches; crossvein r-rs present, connecting pterostigma and Rs; M with three branches; CuA with two branches, ap cell broad; CuP and A ending closely, but not meeting; nodulus absent; in-flight wing-coupling structure simple. Hindwing ( Figure 2D): glabrous; Sc long and ending at 2/3 distal of anterior margin; Rs and M with two branches; CuA and CuP simple; A bifurcate, A1 curved, A2 straight.
Abdomen. Female genitalia strongly sclerotized. Clunium simple, not fused to subgenital plate. Epiproct with short setae, paraproct with long setae. A pair of strong and broad external valves visible in lateral view, appeared out of subgenital plate, with several spurs on the tip of external valve. Subgenital plate broad and strongly sclerotized.

Discussion
Yoshizawa et al. [21] concluded that the suborder Trogiomorpha can be identified based on three morphological apomorphic features: (1) the reduced ventral and dorsal valves; (2) the well-developed external valve close to the ventral midline of the abdomen; and (3) the short subgenital plate, covering at the basal part of the external valves. Therefore, we placed the new genus Brachyantennum gen. nov. into Trogiomorpha based on these characteristics.
Brachyantennum gen. nov. is similar to the two families Cormopsocidae and Prionoglaridiae in the forewing venation, especially in the well-developed and strongly curved Sc, and the presence of a cross-vein between the pterostigma and Rs. Yoshizawa and Lienhard [12] Insects 2022, 13, 1064 6 of 7 considered these characteristics to be the ancestral conditions of Trogiomorpha. The long antennae and the round forewing with an obviously curved anterior margin are considered the apomorphic features of Prionoglarididae [12,22]. All extant members of Prionoglarididae are cave dwellers, but Brachyantennum gen. nov. has no cave-dwelling behavior because of the dark body coloration and the short antennae. Thus, Brachyantennum gen. nov. can be excluded from Prionoglarididae by the dark body coloration, the extremely short antennae, and the slightly curved anterior margin of the forewing.
Brachyantennum gen. nov. is closer to Cormopsocidae than Prionoglarididae, based on the well-developed and very long hindwing Sc vein, which is recognized as the most prominent characteristic of Cormopsocidae by Yoshizawa and Lienhard [12]. The hindwing Sc vein of Cormopsocidae is slightly curved and ends near the mid anterior margin of the hindwing [11][12][13]15,16]. In contrast, the base of the hindwing Sc vein of Brachyantennum gen. nov. is obviously curved, and the Sc vein ends near the 2/3 distal of the anterior margin of the hindwing. However, Brachyantennum gen. nov. is obviously larger than the members of Cormopsocidae in the body and wings. Remarkably, the presence of basal tarsal ctenidiobothria on the mid-and hindlegs is very characteristic of Brachyantennum gen. nov.. In the suborder Trogiomorpha, the tarsal ctenidiobothrium is generally reduced [23]. In the suborder Trocomorpha, the ctenidiobothria are only present on the basal tarsal of the hindleg in a few families, such as Amphientomoidea Enderlein, 1903, and Manicapsocidae Mockford, 1967 [23,24]. In contrast, the presence of basal tarsal ctenidiobothria on the midand hindlegs is generally observed in some families of the suborder Psocomorpha, such as Stenopsocidae Pearman, 1936, and Psocidae Hagen, 1865. Therefore, Brachyantennum gen. nov. can be excluded from the family Cormopsocidae by the tarsal ctenidiobothria.
Based on the discussion above, the placement of Brachyantennum gen. nov. is ambiguous. We tentatively place it into the suborder Trogiomorpha, based on the characteristics of the external valve. However, this genus cannot be assigned to any established families of Trogiomorpha. We do not propose a new family, because it shows numerous plesiomorphic characteristics based on the female individual. The discovery of male materials of this genus would provide more information to determine its placement in the order Psocodea.