Zigrasimecia thate, Abstract, 2023

Abstract, Júlio Cezar Mário Chaul, 2023, A revision of the Cretaceous ant genus Zigrasimecia Barden & Grimaldi, 2013 (Hymenoptera: Formicidae: † Zigrasimeciinae), Zootaxa 5325 (3), pp. 301-341 : 323-324

Zigrasimecia thate Chaul sp. nov.

( Fig. 13 )

Diagnosis (worker). Small species. Head subquadrate in full-face view. Standing setae on body almost entirely absent, except for a patch of long, subflagellate or hook-shaped setae on the frontovertexal region. Small compound eyes. Dorsal mesosomal outline mildly convex; propodeum strongly angled between the dorsal and posterior surfaces. Petiolar node not forming a distinct dorsal surface, the transition from the anterior to the posterior surfaces being a short, curved surface in lateral view; apex of node transversally mildly bilobed.

Examined material. Holotype worker (ANTWEB1038912). Hukawng Valley , Kachin Province, Myanmar; Lower Cenomanian (ca.98.79 ± 0.62 Ma) [ CELC].

Description. Holotype worker. Measurements: HW 0.58, HL 0.62, EL 0.11, ON 32, MesL 0.67, MesH 0.39, PetAFL 0.325, Ptg3L 0.48, Ptg4L 0.20, TL 2.29. Head. In full-face view, head subquadrate, the lateral margins not diverging posteriorly, slightly convex along most of their length (except just posterior to the clypeal lobes where they are slightly concave), and vertexal margin roughly straight. Clypeal lobes well-developed, their width 0.9x the compound eye diameter. Clypeal chaetae count around 30. When mandibles are fully closed, the anteriormost point of the mandible is slightly posterior to the anteriormost point of clypeal lobe (seen in holotype's left mandible). Portion of dorsal surface of mandible, which is ventrally turned, with a filiform, erect seta on its middle. Teeth on masticatory margin of mandible not discernible, but visualization is difficult, as masticatory margin of left mandible entirely occluded by right mandible and basal portion of masticatory margin of right mandible occluded by clypeal teeth. Spiny chaetae on ventral surface of mandible only seen through a gap on the right mandible in full-face view. Labral stout, spiny chaetae only present on the basal-medial area of the labral disc; distal margin wavy, forming two pairs of low, blunt lobes. Labio-maxillary complex including all palpomeres completely concealed by the labrum. Labral distal margin notched medially. Posterior clypeal margin (epistomal sulcus) vestigial, only discernible by a weak angulation on the anterior portion of the head. Frontal carinae small, but well-marked, forming a shallow diagonal scrobe. Numerous, long, equally-spaced, subflagellate or hook-shaped setae on frontovertexal region, their tips (apical quarters) curved medially. Mesosoma. In profile, dorsal mesosoma outline gently convex, meeting an almost straight posterior propodeal margin in a strongly marked angle. Mesosomal dorsum, pleura, and posterior propodeal surface separated by marked, non-carinated, angles. In dorsal view, region likely corresponding to promesonotum gradually tapering to propodeum, the latter about 0.7 times as wide as the former. Propodeum in dorsal view having a concave posterior margin, which descends into a concave posterior surface (not appearing concave in lateral view). Pronotum width 0.5 x head width. Mesopleuron divided into upper and lower sections. Propodeal spiracle slit-shaped, relatively small (0.05 mm, about 0.125 x mesosomal height), mid-height positioned. Metanotal spiracle half the size of propodeal spiracle, positioned at the upper end of the third quarter of mesosomal height. Metanotal spiracle closer to mesonotal spiracle than to propodeal spiracle. Metapleuro-propodeal suture vestigial. Metapleural gland opening subequal in size to propodeal spiracle, with at least a few thin setae around it. Likely only a single spur-like seta present next to the calcar, but difficult to ascertain due to an internal fracture at the level of the apex of left tibiae (confirmation on the right legs difficult due to the positioning of the legs on that side of the body). Metasoma. In anterodorsal view, petiolar node anterior surface subrectangular, its spiracles slightly protruding lower on the lateral margins, and top of node slightly concave. In lateral view the apex of the node being short and curved, barely forming a proper dorsal surface. First gastral tergite roughly convex, not forming conspicuous anterior and dorsal surfaces on the sclerite. No cinctus on A4. Metasoma glabrous, except for A7, which has several curved, long, simple setae on its edge. Sting tip exposed.

Comments. The specimen has little or no distortion or stretching, the cuticle is not damaged or desiccated. The matrix is very clear, but has a fracture that crosses the specimen from side to side, passing in the head at mid-height, in the legs more or less at the tibial level (on the left side), and across the gaster. The fracture does not interfere substantially on the visualization of the ant.

The subflagellate setae on the frontovertexal area are immediately diagnostic of Z. thate . The hook-shaped appereance of the setae could be thought of as preservational, formed by the resistance the resin while the ant was trapped, but since all the setae on the right side are curved opposite to those on the left side, the condition is thus interpreted as a true feature of the species. Zigrasimecia ufv-11, discussed below, have similarly curved setae on the dorsum of head, however, in that morphospecies, the setae are much smaller, appressed, and appear to be thicker.

The pair of setae on the dorsal surfaces of the mandibles ( Fig. 13 , A, black triangles) is clearly seen in Z. perrichoti and Zigrasimecia ufv-11, and might well be common to all Zigrasimecia species although not detected in most specimens due to the difficulties to prospect information inherent of amber specimens.

Etymology. The specific epithet is a non-Latinized portmanteau of part of the names of Thaís Merij Mário and Maria Tereza Mário Chaul, mother and sister of the author, respectively. Thaís and Tereza have financed the studies of the author through the years, including the acquisition of numerous amber specimens such as the ones described in this work.

Figures

FIGURE 13. Holotype of Zigrasimecia thate (ANTWEB1038912). A, full-face view of the head, black triangles indicate mandible dorsal setae; B, profile view of left side of body; C, anterior view of the head; D, dorsal view of the body; E, zoom of flagelliform setae on frons and vertex (same view as C); F, detail of mesosomal profile. Abbreviations: Lmspl, lower mesopleuron; Lmtpl, lower metapleuron; mgo, metapleural gland opening; Ppd, propodeum; Prn, pronotum; sp, spiracles (metanotal and propodeal); Umspl, upper mesopleuron. Scale bars are 0.2 mm in B and D, and 0.1 mm in A.