﻿A new genus and species of minute litter bugs family Schizopteridae Reuter, 1891 from China (Hemiptera, Heteroptera, Dipsocoromorpha)

﻿Abstract A new genus and species of Schizopteridae, Cornonannusbui gen. et sp. nov. is described from Yunnan Province, China. The new genus is closest to Pachyplagia Gross, 1951, Ogeria, Distant 1913, and Kaimon Hill, 2004 in morphology, but it can be distinguished from these genera by the male having a frontal process, the absence of pronotal collar, the distinct venation of forewing, a tarsi formula of 3-3-3, and the middle area of abdominal tergites I to VII with small, round tubercles. Photographs of the male habitus, head, thorax, abdomen, appendages, and genitalic structures, as well as scanning electron micrographs of the male head, thorax, abdomen, and genitalic structures and drawings of male genitalia, are provided. Moreover, a key to all known Chinese schizopterid genera is presented.


Introduction
The Schizopteridae Reuter, 1891 are the most species-rich and widely distributed family of Dipsocoromorpha (the minute litter bugs), and the family currently contains two subfamilies, close to 60 genera, and about 355 species (Schuh and Weirauch 2020).
Schizopterids include the smallest true bugs, ranging in size from 0.8 to 3.0 mm. Most of them have a compact and rotund appearance and are brown or nearly black. Additionally, they sometimes remarkably resemble certain beetles and members of the intertidal dwarf bugs, owing to their coloration and uniformly sclerotized, coleopteroid forewings (Štys 1995). Most of them are ground and litter dwelling, and some species are associated with low herbaceous vegetation, bark, subalpine heath, palm swamp, elevated bogs, moss, grass tussocks, and the nests of ants (Emsley 1969;Hill 1980Hill , 1984Hill , 1987Hill , 1990aSchuh and Weirauch 2020). Biological habits were observed and recorded by Emsley (1969).
Currently, five genera and 18 species of Schizopteridae are recorded from China (e.g. McAtee and Malloch 1925;Ren and Yang 1991;Ren and Zheng 1992;Rédei et al. 2012). Although the species of Kokeshia Miyamoto, 1960 were recently studied (Luo and Xie 2022), the species diversity of schizopterids from China is still poorly known. In this work, a new genus and species, Cornonannus bui gen. et sp. nov., is described, their detailed morphological structures are studied, and a key to all known schizopterid genera occurring in China is provided.

Materials and methods
Specimens were collected in forests by light trapping. Specimens were preserved in 85% ethanol in the field.
External structures and genitalic structures were examined using a Zeiss Discovery V20 stereo microscope. Measurements were taken using a Zeiss Discovery V20 stereo microscope with the software ZEN v. 2.5 pro. Male head, thorax, abdomen, appendages, and genitalia were macerated in warm 10% potassium hydroxide solution (KOH). Habitus, head, thorax, abdomen, appendages, and genitalia were photographed using a Canon EOS 7D Mark II camera equipped with a tube lens and a Mitutoyo M Plan Apo 10× objective lens. Drawings of abdominal segment VIII, pygophore, parameres, and aedeagus were made using a camera lucida from an Olympus CX41 optical microscope under a 40× objective lens. Scanning electron micrographs of abdomen and genitalia of male were prepared using a Phenom Pro Scanning Electron Microscope. Maps were prepared using SimpleMappr (http://www.simplemappr.net/). The type series of the new species is deposited in the Museum of Biology, Sun Yat-sen University, Guangzhou, China (SYSBM).

Taxonomy
Structure: head strongly declivent, short in lateral view, with dense punctures; frons slightly convex, with frontal process in the middle (Figs 2A, C, 5A, C), and several frontal cibarial muscle scars; vertex with cibarial scars consists of five contiguous coarse pits arranged in a row on both sides ( Fig. 2A); areas near inner margin of eyes convex; maxillary plate and buccula with semi-erect, long setae, clypeus with three pairs of semi-erect setae, and one central long seta; labrum with one pair of long setae, labial segment IV with two pairs of long setae (   sinuate, posterior margin slightly convex, middle near straight; proepisternal lobe inflated, almost reaching antennal insertions in lateral view (Fig. 2B). Proepimeral lobe wider than proepisternal lobe, subrectangular, posterior margin of proepimeron sinuate (Fig. 2B). Prosternum with wide longitudinal middle groove, apical portion of prosternal xiphus bilobate, sternal plate of prothorax trapezoidal, with straight posterior margin (Fig. 2C). Mesoscutum large; apex of mesoscutellum projecting posterodorsally in lateral view, base of mesoscutellum with a pair of pits ( Fig. 2D-F); axillary cord sinuated; mesopostnotum with dense tubercles (Fig. 2E, F); mesoepisternal lobe large, mesepimeral lobe narrow, with tongue-shaped apex; upper area of mesopleura with a caudally directed triangular process (Fig. 2 D-F), mesopleura with groove along with middle coxal cleft, a deep concave located near the middle (Figs 2F, 5F); mesosternum with longitudinal mesosternal ridge (Fig. 2F). Metascutum transverse, curved; metapostnotum transverse; a deep groove between mesopleura and metapleural (Figs 2F, 5F). Metasternum with large keellike metasternal spine, interlocking with notch between middle coxal cavities, basal portion of metasternal spine with round process, triangular apex (Figs 2F, 6A); apex of metendosternite bilobate ( Fig. 2D-E). Forewings macropterous in males, female unknown; C+Sc and R thickened, with very narrow, slender subcostal cell; R2 distinctly wider than other veins; basal cell and trapezoidal discal cell slender; end of M subdivided into two branches (Fig. 3A). Hind wings large and subdivided into four lobes, jugal lobe small; Sc+R+M and Cu subequal in length, 1An about three times as long as 2An, m-cu absent, (Fig. 3B). Tarsal formula 3-3-3; apex of coxae, whole trochanters, femurs, tibiae, and tarsi with semi-erect setae (Fig. 3C-E). Arolia absent; pulvilli fine and straight. Inner apex of foretibiae protuberant, with a long seta (Fig. 5E); foretibiae bristle comb with about 10 setae; middle tibiae bristle comb with about 10 setae. Inner surface of hind coxae with adhesive pad (Figs 3E, 6A, B); distal half of hind tibiae slightly curved, apex of hind tibiae with four thick setae. Pregenital abdomen: abdomen strong sclerotized and rigid; terga interlocking, sterna also interlocking; tergites I-VI, sternites II-VI almost symmetric, tergite VII, sternite VII slightly asymmetric, tergite VIII strongly asymmetric ( Fig. 4A-C). Tergites I and II fused, with transverse groove in the middle, tubercles on both sides of groove respectively or only on posterior side of groove (Figs 4B, C, 7A, B). Middle area of sternites II and III less sclerotized, as sockets interlocking with metasternal plate; middle of sternite IV with longitudinal ridge; posterior margin of sternites VI and VII sinuated; sternite VII showing distinct sinistral asymmetry, sternites on both sides are approximately 90° from caudal view (Fig. 4D). Tergite VIII also showing sinistral asymmetry. Genitalia: basal portion of pygophore near globular, overlapped by tergite VIII and sternite VII in repose; apical portion of pygophore flat, and exposed, with dense setae, asymmetrical. Anophore tubular, with anophoric process. Parameres strongly asymmetry; left paramere short, with a broad base, and a curved flattened distal projection; right paramere long, tapering, with a flat oval base provided with inner curved distal projection. Aedeagus complex, with a large, triangular basal plate; apical portion tubular, thin. Etymology. The generic name is derived from the Greek prefix "corn-" (horned or having horns or horn-like appendages) and the Greek root "nannus" (a dwarf ). The gender is masculine. Diagnosis. Same as diagnosis of genus. Description. Macropterous male: small (1.47-1.64 mm), oblong and stout ( Fig. 1A-D). Coloration: ground color brown to dark brown, appendages yellowish brown to light brown, compound eyes dark red, ocelli light brown; punctures on head and prothorax black; distal half and about 2/3 of anterior margin of clavus, basal cell and base of trapezoidal cell of forewings whitish (Fig. 1A, D).

Cornonannus bui
Surface and vestiture: head and prothorax with relatively dense setae, dense hairlike and end-enlarged microtrichia ( Fig. 5A-B, D). Pterothorax with numerous tiny, oblong tubercles and dense microtrichia (Fig. 5F). Veins of forewings with sparse setae. Sterna of abdomen with sparse setae (Fig. 6C), dense microtrichia; area near connexivum with end-enlarged microtrichia (Fig. 6D). Middle region of basal sternite VII with stout-based microtrichia (Fig. 6E), middle region of sternite VII with dense small pits which with radial-ended microtrichia in the middle (Fig. 6F). Tergites of abdomen with tiny, oblong tubercles and dense microtrichia (Fig. 7A-B). Structure: head short; wider than long; frons with up-curved frontal process in middle region (Figs 2A,C,5A,C). Eyes relatively small, minimum width of vertex/ maximum width of eye ca 3.82. Ocelli small, oval. Antennae four-segmented, antennal segment I and II stout, subequal in length, segment III and IV slender, segment IV longer than III, ratio of antennal segments I:II:III:IV = 1:1.05:3.45:4.2. Labium foursegmented, labial segment I thickest, segment IV longest and tapering, ratio of labial segments I:II:III:IV = 1.78:1:1.67:2.33. Thorax: pronotum declivent, near trapezoidal, width about 1.83 times of middle length. Forewings C+Sc and R thicken, with very narrow, slender subcostal cell, R2 about three times the width of other veins (Fig. 3A). Tarsal formula 3-3-3. Forefemurs distinct thicker than middle and hind femurs. Pregenital abdomen: abdomen strongly sclerotized, rigid; tergite I-VI, sternite II-VI almost symmetric, tergite VII, sternite VII slightly asymmetric, tergite VIII strongly asymmetric (Fig. 4A-C); tergites I and II fused, with transverse groove in the middle, and 6-7 round tubercles on both sides of groove respectively; tergites III-VII with transverse groove near basal margin, tergites III-V with 6-7 round tubercles on both sides of groove respectively, tergite VI with four or five round tubercles on both sides of groove respectively, tergite VII with four round tubercles only on posterior side of groove (Figs 4B, C, 7A, B). Tergite VIII also showing sinistral asymmetry, left area depressed which accommodating anophoric process (Fig. 8B). Genitalia: anophore short tubular, with large anophoric process, curving to left; anophoric process with dense spiniform setae on apical region (Figs 7C, F, 8D, E). Left paramere with microtrichia at     base, and oblong flattened distal projection which with two erect setae in dorsal surface; dorsum with hemispherical lobe, which with bilobate margin, two erect setae situated near the concave (Fig. 8G, H); distal projection of right paramere with two semi-erect setae on inner margin (Fig. 8I, J). Aedeagus complex, with a large, triangular basal plate; apical portion tubular, thin, protruding from pygophore about one coil (Fig. 8A, F). Etymology. The specific name is derived from and dedicated to Prof. Wenjun Bu (Institute of Entomology, Nankai University, China), recognizing his contributions to the study of taxonomy, phylogeography and biogeography of Heteroptera, on the occasion of his 60 th birthday.

Discussion
The genus Cornonannus gen. nov. is morphologically most similar to Pachyplagia Gross, 1951, Ogeria, Distant 1913, and Kaimon Hill, 2004, but it also has significant differences from these three genera (Table 1). Until now, special organs on the head of schizopterids has been thought to be rare. Except for the new genus and species, the other cases are as follows: male with bilobed frontal process, a synapomorphy of the genus Voragocoris Weirauch, 2012 (Weirauch 2012); male vertex of Kaimon usually with conspicuous pit or U-shaped groove and lobe (Hill 2004); some Membracioides species with vertex organ (Knyshov et al. 2019); and several Hypselosoma species with male labral organ. Biology of the new species is poorly known, but females of Cornonannus bui sp. nov. were not found with the males. Similar to its allies, females of this species are speculated to have brachypterous or micropterous forewings. As for body color, it is not uncommon for the color pattern of forewings of C. bui sp. nov., similar pattern also appear in species of Corixidea Reuter, 1891, Ommatides Uhler, 1894, Chinannus Wygodzinsky, 1948, Pachyplagia Gross, 1951, Voragocoris, Hypselosomops Hoey-Chamberlain & Weirauch, 2016, and Perittonannus Weirauch, Knyshov & Hoey-Chamberlain, 2020. Considering that this color pattern generally occurs in both sexes, it may be related to cognate recognition.