A New Species of Vetubrachypsectra from Mid-Cretaceous Amber of Northern Myanmar (Coleoptera: Brachypsectridae)

Simple Summary Brachypsectridae is a small family in the superfamily Elateroidea, with only two extant and two extinct genera known based on adults. Here, we figure and describe a new brachypsectrid species from the mid-Cretaceous amber of northern Myanmar, based on an exceptionally well-preserved female specimen. Although sexual dimorphism is common in Brachypsectridae, this specimen is recognized as a new species, rather than a female of the previously reported V. burmitica, primarily based on its different pedicel–scape attachment. Abstract A new species, Vetubrachypsectra huchengi Li, Kundrata & Cai sp. nov., is described from mid-Cretaceous Burmese amber on the basis of a single adult female. The species is assigned to genus Vetubrachypsectra Qu & Cai based on its serrate antennae, long maxillary palps, presence of tibial spurs, and elytra without clear striae. Vetubrachypsectra huchengi differs distinctly from V. burmitica Qu & Cai, the only other species in the genus, in having the pedicel apically attached to the scape. Some other differences between the female of V. huchengi and the male of V. burmitica include less serrate antennae, a broader pronotal disc, a broader scutellar shield and smaller tibial spurs. However, at least some of these characters can be considered sexually dimorphic.


Introduction
Brachypsectridae is a small family in the superfamily Elateroidea. The whole family was known from a single extant genus, Brachypsectra LeConte, until the discovery of Asiopsectra Kovalev & Kirejtshuk in 2016 [1]. Brachypsectra currently comprises seven extant species and have been reported from various sites around the world, including the southwestern part of North America, the Dominican Republic, Turkey, Iran, Cyprus, India, and Singapore [2][3][4][5][6][7], while two species of Asiopsectra are only known from Tajikistan and Iran based on a single male specimen each [1]. Adults of brachypsectrids generally share a similar habitus with other hard-bodied elateroid taxa [8], though without a functional prothoracic "clicking mechanism" [9]. Larvae of brachypsectrids, in contrast, are quite peculiar in having branched lateral lobes on the thorax and abdomen [2][3][4]7,8,[10][11][12]. Two recent large-scale phylogenetic studies, using morphological (implied weighted parsimony) [13] and molecular (Bayesian) [14] data, respectively, suggested Brachypsectridae as sister to a group comprised of Throscidae, Eucnemidae, and Cerophytidae, although in the latter study [14], analysis under maximum likelihood found Brachypsectridae sister to the "higher Elateroidea" sensu Kundrata et al. [15].
The easily distinguishable larval fossils of Brachypsectridae have been reported from Miocene Dominican amber [3,4,16], Eocene Baltic amber [12,16], and mid-Cretaceous Burmese amber [12,17]. An adult fossil of Brachypsectra is also known from Dominican amber [4]. Recently, two fossil genera of Brachypsectridae were established based on adults found in Burmese amber. Hongipsectra Tihelka et al. is distinctive in having 11-segmented bilamellate antennae in males and a posterior pronotal margin with an M-shaped medial notch [18]. Vetubrachypsectra Qu & Cai is morphologically similar to Brachypsectra, although it can be separated from the latter based on the longer maxillary palpomere 3, presence of tibial spurs, and parameres without a hook [19]. Genus Cretopsectra was erected based on a larva in Burmese amber [17], which is problematic because it might belong to some previously described species, as noted by Haug et al. [12]. In the current study, we report an additional new species of Vetubrachypsectra based on a single female from Burmese amber, and re-examine the holotype of V. burmitica using confocal microscopy.

Materials and Methods
The Burmese amber specimens studied herein, i.e., holotypes of both species of Vetubrachypsectra, originated from amber mines near Noije Bum (26 • 20 N, 96 • 36 E), Hukawng Valley, Kachin State, northern Myanmar. Both specimens are deposited in the Nanjing Institute of Geology and Palaeontology (NIGP), Chinese Academy of Sciences, Nanjing, China. The amber piece containing the new species was trimmed with a small table saw, ground with emery paper of different grit sizes, and finally polished with polishing powder.
Photographs under incident light were taken with a Zeiss Discovery V20 stereo microscope. Widefield fluorescence images were captured with a Zeiss Axio Imager 2 light microscope combined with a fluorescence imaging system. Confocal images were obtained with a Zeiss LSM710 confocal laser scanning microscope, using the 488 nm (Argon; for V. huchengi sp. nov.) or 561 nm (DPSS 561-10; for V. burmitica) laser excitation lines [20]. Fluorescence images could illustrate the structures better than brightfield ones, as the fluorescence emitted around the border between the inclusion and amber matrix clearly shows the boundary of structures. In confocal microscopy, the out-of-focus background fluorescence produced by the amber matrix is further blocked, leading to a higher signalto-noise ratio [20]. Images under incident light and widefield fluorescence were stacked in Helicon Focus 7.0.2 or Zerene Stacker 1.04. Confocal images were stacked with Helicon Focus 7.0.2 and Adobe Photoshop CC. Images were further processed in Adobe Photoshop CC to adjust brightness and contrast.
This published work and the nomenclatural act have been registered in ZooBank, the official registry of Zoological Nomenclature.
Remark. This species is placed to Vetubrachypsectra based on the elongate maxillary palpomere 3, presence of tibial spurs, and elytra without clear striae [19].

Discussion
Currently, there are two extant and two extinct genera (with adults known) in Brachypsectridae [1,4,18,19]. The extinct genus Vetubrachypsectra differs from the other three genera in having the combination of unipectinate/serrate antennae, an elongate maxillary palpomere 3, the presence of tibial spurs, and elytra without clearly defined striae.
Compared to the previously published male of V. burmitica Qu & Cai (Figure 4) [19], the female of V. huchengi sp. nov. exhibits several different characters (Figures 1-3). The pronotum is only moderately convex dorsally, about 1.3 times as wide as long, and with less rounded sides in V. burmitica, while it is more robust and convex dorsally, 1.5 times as wide as long, and with clearly rounded sides in V. huchengi sp. nov. In V. burmitica, the antenna is distinctly pectinate in antennomeres 4-10, while it is distinctly serrate only in antennomeres 7-10 in V. huchengi sp. nov. The posterior margin of the outer portion of metacoxal plates in V. burmitica is more or less straight, but it might be gradually rounded in V. huchengi sp. nov. (at least as seen in the right metacoxal plate). Additionally, V. huchengi sp. nov. has a distinctly broader scutellar shield (wider than long vs. longer than wide) and less well-developed tibial spurs.
Modern members of Brachypsectra display some sexual dimorphism in body size and shape, with females being generally larger and broader, and having less pectinate/serrate antennae and a somewhat anteriorly inflated pronotal disc [4,6]. Similar dimorphism has also been suggested for the fossil genus Hongipsectra from Burmese amber [18]. The less prominently serrate (and not pectinate) antennae, more transverse and dorsally convex pronotal disc, broader scutellar shield and smaller tibial spurs of V. huchengi sp. nov. (all or only some of them) may actually represent sexually dimorphic characters as well. However, the specimen of V. huchengi has the pedicel apically attached to the scape ( Figure 3A), while V. burmitica has the pedicel attached to the scape subapically ( Figure 4A,G) [19]. Since both specimens are well preserved and there are no differences between right and left antenna within the same specimen, this character cannot be classified as an artifact due to the pressures during the formation of the amber piece. However, such a character is not known as sexually dimorphic in any Brachypsectridae known so far. Actually, the subapical attachment of pedicel to scape is used for diagnoses of higher-ranked taxa (Cerophytidae and Eucnemidae) rather than species. Thus, the attachment of pedicel is very unlikely to be a sexually dimorphic character, and we suggest V. huchengi sp. nov. should represent a separate species, rather than the female of V. burmitica.