New mimarachnids (Hemiptera, Fulgoromorpha, Fulgoroidea) in mid-Cretaceous Burmese amber

Abstract A new genus and species, Multistriaorthotropagen. et sp. nov., and a new species, Dachibangushuisp. nov., of Mimarachnidae are described from the mid-Cretaceous Burmese amber. These new taxa display unique wing color patterns and extend the Mesozoic diversity of Mimarachnidae. The evolution of wing venation, phylogenetic placement of Mimarachnidae, and anti-predation defenses of this family in Burmese amber forest are briefly discussed.


Introduction
Mimarachnidae Shcherbakov, 2007 is a small, extinct family belonging to the diverse phytophagous superfamily Fulgoroidea. They are medium-sized to large planthoppers and are characterized by the following characters: mesonotum with double median carinae, remnants of sensory pits in the adults, tegmina and hind wings with simplified venation and irregular network of veinlets, and basal cell absent or weak (Brysz and Szwedo 2019). Historically, species of this family were considered as members of the "cixiidae-like" planthoppers (Bourgoin and Szwedo 2008), and some mimarachnids are specialized insects with peculiar and striking forms (Shcherbakov 2007;Jiang et al. 2018Jiang et al. , 2019Zhang et al. 2018).
Herein, we describe a new genus with a new species, Multistria orthotropa gen. et sp. nov., and a new species, Dachibangus hui sp. nov., of Mimarachnidae from the mid-Cretaceous Myanmar. Both new species possess well-preserved wing venation and color pattern.

Materials and methods
The specimens (contributed by Mr Zhengkun Hu) described in this study are from the Burmese amber collected from Hukawng Valley of Kachin in northern Myanmar (Li et al. 2017). The age of the Burmese amber is estimated to be the earliest Cenomanian, ~98.79 ± 0.62 Ma (Shi et al. 2012). Burmese amber from this site contains diverse insects (Ross 2021). The type specimens are housed in the Key Lab of Insect Evolution and Environmental Changes, College of Life Sciences, Capital Normal University, Beijing, China (CNUB; Yunzhi Yao, Curator).
The amber specimens were examined and photographed using a Nikon SMZ 25 microscope with an attached Nikon DS-Ri 2 digital camera system. The line drawings were made with Adobe Illustrator 2020 and Adobe Photoshop 2020. The wing venational nomenclature follows that of Bourgoin et al. (2015). Etymology. The generic name is a combination of Latin "multi-" meaning "many" and "stria" meaning "streak", referring to its wrinkled posterior pronotum. Gender feminine.

Order
Type species. Multistria orthotropa Zhang, Yao & Pang, sp. nov. Diagnosis. Pronotum with posterior area rugulose (not rugulose in Dachibangus). Tegmen costal area narrow, exceeding 2/3 length of the wing, ScP + RA and RP single, close to each other, subparallel, MP with three terminals (no fewer than five terminals in Dachibangus), CuA forked early, near wing basal 1/3, CuA 2 slightly curved mediad at level of tornus (more curved in Dachibangus). Without narrow marginal membrane. Hind wing CuA with two terminals. Etymology. The specific name is from a Latin word "orthotropus" meaning "straight", referring to its median carinae of mesonotum straight.
Diagnosis. Pronotum with anterior margin almost straight, posterior margin slightly concave, median carinae of mesonotum straight. Tegmen without spots, common stem ScP + R shorter than basal cell, Pcu almost straight, free part of Pcu distinctly shorter than common stem of Pcu + A 1 . Metatibio-metatarsal formula 5: 5: 5.
Description. A well-preserved specimen, but ventral view not visible; total length of the holotype about 15.98 mm.
Head: head with compound eyes about 2.52 mm wide, wider than half of pronotum width. Vertex triangular, without median carina, lateral margins carinate, posterior margin sinuous, trigons visible in dorsal view.
Thorax: pronotum subhexagonal, length distinctly shorter than mesonotum, about 4.3 times as wide as long in midline, posterior area of pronotum rugulose, anterior margin almost straight, posterior margin arcuate and concave, median carinae double and parallel, present throughout, lateral carinae invisible. Mesonotum poorly preserved, wider than long in midline, median carinae parallel and paired, diverging laterad on scutellum, lateral carinae invisible, scutellum indistinct. Tegula subquadrate, large and distinctly carinate.
Leg: only part of hind leg visible, covered with short setae. Hind tibia widened apically, with five apical teeth; hind tarsi with three segments, basitarsomere 1.72 mm long, distinctly longer than combined length of midtarsomere and apical tarsomere, with five apical teeth, the external teeth longer than inner group; midtarsomere 0.89 mm long, with five apical teeth, the external teeth longer than inner group; subapical setae on all pectens invisible; apical tarsomere 0.67 mm long; tarsal claws developed, arolium wide.
Wings: membranous. Tegmen 14.03 mm long, 5.55 mm wide, about 2.5 times as long as wide, with distinct venation and irregular network veinlets, and also with irregular colour bands from base to apex, costal margin weakly arched at base, anteroapical and posteroapical angles broadly rounded, posterior margin straight, tornus present. Costal area narrow and long, with transverse veinlets, narrowing toward wing apex, basal cell weak, arculus indistinct, Pc + CP extends nearly to wing apex, apical portion invisible, common stem ScP + R + M longer than common stem ScP + R, branch ScP + RA and RP subparallel to costal margin, not forked, stem MP curved at base then almost straight, forked in wing apical half, with three terminals, branch MP 1+2 forked, reaching margin with two terminals, branch MP 3+4 simple, CuA forked near wing basal one-third, with two terminals, CuA 1 basally subparallel to CuA 2 , CuA 2 slightly curved mediad at level of tornus, CuP present throughout wing, slightly sinuate, clavus open, Pcu and A 1 fused nearly at the same level of CuA forking, free part of Pcu distinctly shorter than common stem of Pcu + A 1 , narrow marginal membrane absent. Hind wing membranous, about 11.01 mm long, 6.60 mm wide, slightly shorter than tegmen, coloration of hind wing darker, two lighter irregular spots near posteroapical portion, irregular network veinlets present. Anteroapical angle round, ScP + R forked, with two terminals, ScP + RA curved in apical portion, stem MP single, CuA forked at wing midlength, reaching margin with two terminals, CuP almost straight, Pcu slightly sinuous.

Remarks.
The new genus is assigned to Mimarachnidae based on the following characters: mesonotum with double median carinae, remnants of sensory pits at the adults, wings with simplified venation, and irregular network of veinlets, basal cell weak, hind wing MP simple. This new genus is distinguished from other genera by the following characters: posterior area of pronotum rugulose (vs no such character in the other known genera); tegmen costal area exceeding 2/3 length of the wing (vs less than ½ of wing length in Chalicoridulum, Ayaimatum, and Mimaeurypterus, costal  Diagnosis. Median carinae of mesonotum straight, subparallel to each other, lateral carinae posterior portion nearly straight (median carinae slightly sinuate, lateral carinae posterior portion arcuate in D. trimaculatus); tegmen without spots (with spots in D. trimaculatus and D. formosus); common stem ScP + R as long as basal cell (ScP + R longer than basal cell in D. formosus, ScP + R about 1/2 of basal cell in D. trimaculatus); MP with five terminals (six terminals in D. trimaculatus); the bifurcation of MP 1+2 slightly proximad of the bifurcation of MP 3+4 (the bifurcation of MP 1+2 slightly apicad of the bifurcation of MP 3+4 in D. formosus); CuA 1 almost straight (arcuate in D. trimaculatus); CuA 2 slightly curved mediad at level of tornus (more curved in D. formosus, strongly curved in D. trimaculatus); CuP almost straight (sinuate in D. trimaculatus and D. formosus); free stem of Pcu nearly as long as common stem of Pcu + A 1 (Pcu longer than Pcu + A 1 in D. trimaculatus); CuP and Pcu + A 1 not close to each other (close to each other in D. trimaculatus); hind wing CuA forked at wing midlength (forked near wing base in D. trimaculatus).
Description. Total length of the preserved holotype about 14.21 mm, wings well-preserved.
Wings: membranous. Tegmen 13.59 mm long, 5.06 mm wide, about 2.7 times as long as wide, with distinct venation and irregular network veinlets, and also with irregular colour bands from base to apex, costal margin weakly arched at base, apical margin round, posterior margin almost straight, tornus distinct. Costal area narrow and long, with transverse veinlets, narrowing toward tegmen apex, basal cell weak, arculus weak, Pc + CP parallel to costal margin, apical portion weakened, common stem ScP + R + M approximately as long as common stem ScP + R, ScP + RA not forked, posterior portion curved upward, then downward to apical margin, apical portion weakened, RP single, apical portion weakened, stem MP almost straight, forked in wing apical half, with five terminals, the bifurcation of MP 1+2 slightly proximad of the bifurcation of MP 3+4 , MP 1+2 reaching margin with three terminals, MP 3+4 with two terminals, CuA forked near wing basal one-third, with two terminals, CuP present throughout wing, nearly straight, clavus open, Pcu and A 1 fused apicad of CuA forking, narrow marginal membrane absent, wing-coupling fore fold present.
Hind wing membranous, about 10.57 mm long, 5.63 mm wide, slightly shorter than tegmen, without distinct coloration, irregular network veinlets present. Anteroapical angle round, stem ScP + R straight, forked late, with two terminals, ScP + RA apical portion curved, MP single, CuA forked at wing midlength, with two terminals, CuP almost straight, apical portion absent, Pcu weakly sinuous, A 1 forked, giving off two branches.
Remarks. The new species is attributed to the genus Dachibangus due to mesonotum median carinae diverging laterad on scutellum, lateral carinae strongly diverging posteriad, tegmen with irregular colour bands, costal area narrow, ScP + RA curved downward in apical portion, MP at least with five terminals, CuA 2 curved mediad at level of tornus, tornus distinct.

Discussion
Including the new taxa described in this study, Mimarachnidae now comprise 13 genera and 19 species, all confined to the Cretaceous. Among them, five genera and five species have been described from the early Cretaceous of Russia, Spain, and Japan, and the rest were discovered from the mid-Cretaceous Burmese amber. During early Cretaceous period, tegmen ScP + RA and RP of mimarachnids were generally forked, with the MP having 2 or 3 terminals, such as in Mimarachne, Saltissus, and Mimamontsecia. However, by the mid-Cretaceous, tegmen ScP + RA, and RP were unbranched (all species) and the MP single (Cretodorus) or with 2 or 3 terminals (Burmissus, Mimaplax, Ayaimatum, and Mimaeurypterus) or with no fewer than 4 terminals (Jaculistilus and Dachibangus). Therefore, we speculate that the number of tegmen ScP + R terminals gradually reduced, and the number of MP terminals seems to have been diversified during the evolutionary process of Mimarachnidae.
The placement of Mimarachnidae in Fulgoroidea remains unclear. Shcherbakov (2007) placed Mimarachnidae in the "pre-cixioid section of Fulgoroidea" and related them to Perforissidae. Subsequently, this family was generally assigned into the "cixiidae-like" planthopper group (Bourgoin and Szwedo 2008;Szwedo and Ansorge 2015;Brysz and Szwedo 2019), which is an informal group comprises some extinct and extant families similar to Cixiidae. Mimarachnidae are unique planthoppers in the Mesozoic. Mimarachnidae and Perforissidae share many similar characters such as the simplified venation, remnants of sensory pits at the adults, destabilization of hind leg armature (Shcherbakov 2017). But, as Jiang et al. (2018) suggested, these similarities are also shared by various families of Fulgoroidea. These similarities cannot support a close relationship between Mimarachnidae and Perforissidae because they could also result from convergent or par-allel evolution. Besides, Mimarachnidae and the "cixiidae-like" families show obvious differences in the morphology, such as venation patterns, shape of head and thorax, and number of carinae, which suggests that they do not form a lineage and share a common ancestor. A robust placement of Mimarachnidae in Fulgoroidea still needs further study.
Fulgoromorpha are phytophagous insects. These planthoppers stay on the host plants for a long time to suck fluids, with wings covering their bodies. Colour pattern of the wings might have become important for serving as a defensive strategy to disguise themselves from enemies. In Multistria gen. nov. and Dachibangus, the tegmina are covered with irregular color bands from the base to the apex, contrasting highly and extending to the tegmina edges. This disruptive coloration could effectively break up the shape and destroy the outline of the insects Merilaita 2009a, 2009b), and thereby make these larger planthoppers more difficult to be detected. Similarly, in D. trimaculatus Jiang, Szwedo & Wang, 2018, D. formosus Fu, Szwedo, Azar & Huang, 2019, and Jaculistilus oligotrichus Zhang, Ren & Yao, 2018, the dark wing spots are obvious and may also have anti-predation function (Théry and Gomez 2010). In addition, Mimaplax ekrypsan Jiang, Szwedo & Wang, 2019 used more complicate camouflaged configuration to avoid possible predation. It is possible that mimarachnids have evolved with a range of anti-predation defenses in Burmese amber forests, such as disruptive coloration, wing spots, and "flatoidinisation syndrome" (a specialized and complex camouflage, uniting shape, colour, and behaviour) (Jiang et al. 2019) to help them to avoid being attacked by predators.