﻿Primitive new termites (Blattodea, Termitoidae) in Cretaceous amber from Myanmar

﻿Abstract Mastotermitidae, the first-diverging extant family of termites, has only one relic extant species; however, this family had greater richness during the Mesozoic and Cenozoic eras. Fossil termites from the Cretaceous provide information on the early evolution of termites and the transition between extinct families. Herein, two new Mastotermitidae species found in upper Cretaceous (Cenomanian) Kachin amber are reported. One is a female imago described as Angustitermesreflexusgen. et sp. nov. and assigned to the subfamily Mastotermitinae. The other is Mastotermesreticulatussp. nov., which is described from an isolated forewing. With the comparison especially of the antenna and venation, these new mastotermitids further increase our knowledge of the diversity and morphology of Mastotermitidae during the Mesozoic.


Introduction
Termites are social insects with the support of mutualistic protists or cellulose-digesting bacteria (Breznak and Brune 1994;Sanderson 1996;Sugimoto et al. 2000;Krishna et al. 2013a;Zhao et al. 2020Zhao et al. , 2021)).The enormous biomass of termites largely contributes to the global carbon cycle, while occupying an important ecological position in the biosphere (Tuma et al. 2020).The rank of termites has been controversial.Inward et al. (2007) indicated that the rank of termites should be a family, however, some termitologists proposed to continue using "Isoptera" (Lo et al. 2007), and the current compromise is to use "epifamily Termitoidae" (Eggleton et al. 2007;Bignell et al. 2011;Xiao et al. 2012;Beccaloni and Eggleton 2013;Zhao et al. 2019) or "infraorder Isoptera".
As the first-diverging extant family in Termitoidae (Thompson et al. 2000;Legendre et al. 2015;Bucek et al. 2019;Zhao et al. 2019), Mastotermitidae ZooKeys 1197: 115-126 (2024), DOI: 10.3897/zookeys.1197.114452 Yurong Jiang et al.: Primitive new Termitoidae in Cretaceous amber from Myanmar shares many characters with cockroaches, for example, a large anal lobe in the hind wing and vestigial ootheca or egg pod (Nalepa and Lenz 2000;Krishna et al. 2013a).The most obvious morphological differences from other termite families are that the hind wings have large anal lobes and Sc, R, Rs, and M veins are thick and more sclerotized than CuA.Mastotermitidae was divided into two subfamilies, Mastotermitinae Desneux, 1904 and Idanotermitinae Engel, 2021, based on the presence or absence of ocelli (Jiang et al. 2021).

Materials and methods
The two specimens studied here were collected from amber mines located in the Hukawng Valley in Kachin State of northern Myanmar.Determined by U-Pb dating of Zircon, the deposit age of the amber mine was 98.79 ± 0.62 Ma which means it comes from early Cenomanian of the upper Cretaceous (Shi et al. 2012).The amber specimens involved in this study were acquired by Mr Fangyuan Xia before 2015 and donated for this study in 2016.Both specimens are deposited in the Key Laboratory of Insect Evolution and Environmental Changes, College of Life Sciences, Capital Normal University, Beijing, China (CNUB, curator: Dong Ren).
The amber is cut and polished.The specimens are examined, measured, and photographed with a Nikon SMZ25 microscope system.To help reduce picture distortion caused by refraction and internal cracks, the amber was placed in a properly sized crystallizing dish, with a proper amount of water, and the capture angle and area of interest was adjusted when viewing; the amber was affixed with plasticine when measurements and photographs were taken.
All images are stacked using the software Helicon Focus v. 8 for better depth of field.Simplified drawings were prepared using Adobe Illustrator CC and further modified using Adobe Photoshop CC.Type species.Angustitermes reflexus Jiang, Z. Zhao & Ren,.
Etymology.Angusti-is a Latin adjective, reflecting the fact that the medial field of this genus is narrow, and termes is the usual noun for the generic name in Termitoidae.The gender is masculine.
Diagnosis.Imago: ocelli oval; fontanelle absent; Y-suture absent; mandibles not exceeding labrum; antenna moniliform with 22 articles; compound eyes lying in middle position on head; pronotum saddle-shaped.Wings heavily reticulated, with "cross-veins" present.Forewing: scale large, overlapping hind wing base, humeral suture convex; all major veins origin in scale; veins Sc, R 1 , R 2 , Rs, and M more pigmented than CuA; Sc simple; Rs with about three main branches, terminating on costal margin anterior to wing apex; radial field narrow, parallel to costal margin; M closer to Rs than CuA, lying more or less parallel to Rs as a simple vein for the greater part of its length, first branching in apical 1/5 of wing length, medial field narrow, encompassing wing apex; CuA branched, lying above the mid-longitudinal line of wing; CuP (claval suture) arched, meeting basal suture before posterior margin.Hind wing: basal suture not visible, large anal lobe present.Legs: tibial spines of all legs present; tibial spur formula 3-4-4; tarsi pentamerous; arolium present.Abdomen: cerci short, trimerous; abdominal styli absent.
Remarks.Based on the sclerotized vein M, presence of the anal lobe, saddle-shaped pronotum, pentamerous tarsi, etc., Angustitermes gen.nov. is considered to belong to the Mastotermitidae and is assigned to the subfamily Mastotermitinae because of the ocelli (Fig. 1C).Besides the new genus and Mastotermes, there are two other genera in Mastotermitinae: Garmitermes Engel, Grimaldi &Krishna, 2007 andMagnifitermes Jouault, Engel &Nel, 2022.Termites in both Angustitermes gen.nov.and Garmitermes have a rounded head, but unlike Angustitermes gen.nov., Garmitermes has 26 antennal articles, the arolium is greatly vestigial or absent, and the tibial spur formula of Garmitermes is 3-5-4 (Engel et al. 2007).Both Angustitermes gen.nov.and Magnifitermes have arolium, and their tibial spur formula is the same.However, the shape of the head of Magnifitermes is relatively long and with about 28 antennal articles (Jouault et al. 2022).Although in different subfamilies, Angustitermes gen.nov.and Anisotermes share many similarities, such as the rounded head and the tibial spur formula.However, the M vein of Anisotermes is located halfway between Rs and CuA, and the first inferior branch of the M vein on the hind wings gradually fades away, ultimately terminating in the center of the hind wings of Anisotermes (Zhao et al. 2019;Jouault et al. 2022).
The major feature of Angustitermes gen.nov. is that the M vein is a simple vein for the greater part of its length, first branch branching in the apical 1/5 of wing length, and the medial field is narrow (Fig. 2B).The simple M and narrow medial field of Angustitermes gen.nov. is similar to Blattotermes Riek, 1952.However, Angustitermes gen.nov.has sparser veins than Blattotermes; the branches of R and secondary branches of CuA are fewer, and tertiary branch is absent; its forewings are much shorter, so that the difference in wing lengths between these two genera is more than 10 mm.Besides, the specimen of the new Angustitermes species is from the upper Cretaceous while the three Blattotermes species are from the Cenozoic: Blattotermes neoxenus Riek, 1952 and Blattotermes wheeleri (Collins, 1925) are from Eocene, and Blattotermes massiliensis Nel, 1986 is from Oligocene (Collins 1925;Riek 1952;Nel 1986;Thorne et al. 2000;Krishna et al. 2013b).Etymology.The specific name, reflexus, means "fold", which is in reference to the fact that the right forewing and right hindwing of the holotype are folded.The gender is masculine to match gender of the genus.

Angustitermes reflexus
Locality.The specimen was collected from the upper Cretaceous (Cenomanian) deposits of the Hukawng Valley, Kachin State, northern Myanmar.
Diagnosis.As for the genus.Description.Imago: head length 3.38 mm, width 2.99 mm (excluding sizes of compound eyes), with sparse setae; labrum sclerotized, connecting to anteclypeus, width longer than length, anterior margin with short setae; apical tooth of mandibles not reaching the apex of labrum, first marginal tooth and apical tooth of left mandible divided in acute angle, other marginal teeth not visible; width of anteclypeus and postclypeus much longer than length; antenna with 22 articles; compound eyes hemispheric, slightly flat, diameter about 0.67 mm, lying on the middle position of the head, ommatidia diameter about 0.02 mm.Pronotum pilous, width about 3.35 mm, centraxonial length 1.97 mm, almost breaking away from the head.Wings long and broad with apex rounded, length 13.91 mm (excluding forewing scale), scale length 2.17 mm, wing width 5.02 mm; reticulated veins obviously pigmented among radial field and medial field, basal 5/8 of right hind wing hidden under right forewing.Forewing: scales with sparse setae, humeral margin convex, with weakly arched lobe present, basal suture curved; Sc simple, terminating on basal quarter of wing length; R with two branches in scale, terminating along anterior wing margin at half wing length; Radial field occupying about 1/8 wing area, left forewing with four branches, first branching at basal 1/3 of wing length, right forewing with three branches, first branching at basal 1/4 of wing length; M with two branches, branching at apical 1/5 of forewing; right CuA first branching in scale, occupying about 3/4 right forewing with three main branches, the branch near M vein branching at 1/2 of the wing length, the next branch branching near the middle of the wing to the base, and the branch near posterior margin branching in scale.Hind wing: basal suture not visible; large anal lobe present; left Rs with two branches branching from M at base; M with three branches.Legs: different degrees of damages to the legs, the left pro- tarsus not preserved and the distal part of protibia not visible, the right mesotrochanter expanded and ruptured, and the large area of the left metacoxa broken; tibial spurs and spines not serrated.Abdomen: abdomen fragmentary, some of the detached abdominal segments can be observed, including the distal abdominal segments with a pair of cerci.Cerci trimerous; abdominal styli absent.
Etymology.Latin, reticulatus, meaning "reticulate", which is in reference to the well-developed and clearly recognizable reticulated veins of holotype.Locality.The specimen was collected from the upper Cretaceous (Cenomanian) deposits of the Hukawng Valley, Kachin State, northern Myanmar.
Diagnosis.Forewing: wing length (excluding forewing scale) about three times as long as wide; forewing scale large; heavily reticulated, irregular bilayer structure in M and CuA, cross veins between Rs and M obvious; Sc, R, Rs, and M thickened, strongly sclerotized and obviously pigmented; Sc and R 1 simple and short; Rs with seven or eight branches, with secondary branches, running parallel to costal margin; M with six branches, first branch of M arising at forewing mid-length, secondary branches present, medial field encompassing wing apex, angle of branches and main vein gradually increasing.
Description.Forewing: forewing length (excluding forewing scale) 13.2 mm, width about 4.7 mm; suture length about 2.3 mm, strongly arched, making a sharp angle with posterior margin; distal costal margin slightly missing, posterior margin partially missing because of abrasion of the amber; base of costal margin rolled up, making the Sc and R poorly visible; Sc length 1.0 mm; R 1 length 2.0 mm, Rs with eight branches; M slightly closer to Rs than to CuA, encompassing wing apex, six branches visible, angle of branches and main vein gradually increasing, so that branches terminate closely on margin, first branch of M arising at forewing mid-length, second branch arising at about distal third of forewing length, and base of third branch close to fourth branch with secondary branch.
Remarks.The forewing of Mastotermes reticulatus sp.nov. is similar to that of Mastotermes monostichus Zhao, Eggleton & Ren, 2019, but there are some differences; the Sc, R, and Rs of Mastotermes reticulatus sp.nov.are closer, and there are fewer secondary branches, which makes the Rs veins parallel to the costal margin, instead of gradually narrowing as in M. monostichus.Compared with M. monostichus, the M vein of M. reticulatus sp.nov. is even more irregular and with fewer branches (Fig. 4).These different characteristics indicate that they are not the same species.

Discussion
The number of antennal articles in Angustitermes reflexus gen.et sp.nov. is only 22 (Fig. 2B), which is fewer than in most mastotermitids, especially the range of 29-32 of the extant Mastotermes darwiniensis (Krishna et al. 2013a), even though the antennae of many fossil termites are incompletely preserved.Another mastotermitid, Mastotermes minutus Nel &Bourguet, 2006 (Nel andBourguet 2006), which was described from Early Eocene amber of Oise (France), has the fewest antennal articles, with only 20.Other mastotermitids that have been reported with complete antennae have more than 24 antennal articles.In addition to the antennae and the synapomorphies of mastotermitids, there are many similarities between Mastotermes minutus and Angustitermes reflexus gen.et sp.nov.: an ocellus is present, which indicates that they belong to the same subfamily; M of the hind wing branches from Rs, close to the wing scale; meso-and metatibiae have at least three lateral spines; tibial spurs are 3-4-4; and an arolium is present.However, these species also have some differences: the M vein of Angustitermes reflexus gen.et sp.nov. is closer to Rs than Cu (Fig. 2B), while the M vein of Mastotermes minutus is closer to Cu than to Rs.In terms of geological time, the number of antennal articles within Mastotermitidae seems to change from many (plesiomorphic state) to few and then back to many.Further phylogenetic analysis with more fossil mastotermitids may clarify the specific trend of the evolution of the number of antennal articles in Mastotermitidae.
The sclerotized vein M of the forewings in Angustitermes reflexus gen.et sp.nov.are relatively simple, with only two branches and the medial fields, located in the anterior third, compressed.Concurrently, the distal-most branches of CuA, which end at the wing apex, are also thick and sclerotized, similar to M, and stronger than the other branches of CuA (Figs 2,3A).This is opposite in the wings of Mastotermes reticulatus sp.nov., Anisotermes xiai, and Mastotermes monostichus, which have multibranched M in the forewing, with the basal-most branches gradually tapering and unsclerotized.Mastotermitids share a synapomorphy: the Sc, R, Rs, and M veins are thicker and much sclerotized than CuA (Engel et al. 2009;Zhao et al. 2019).The synapomorphy tends to indicate the overall degree of sclerotization present in each vein, and some branches with different locations may show different degrees of thickness and sclerotization.