Zigrasimecia caohuijiae, 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 : 313-316

Zigrasimecia caohuijiae Chaul, sp. nov.

( Figs. 7–8 )

Diagnosis (worker). Small species. Head round in full-face view. Standing setae on body absent, except for tiny pubescence across the body. Dorsal mesosomal outline conspicuously convex; propodeal dorsal and posterior surfaces not separated from one another by a strongly marked corner. Petiolar node dorsal surface developed, round.

Examined material. Holotype worker (ANTWEB1041055). Hukawng Valley , Kachin Province, Myanmar; Lower Cenomanian (ca.98.79 ± 0.62 Ma) [ CELC].

Description. Holotype worker. Measurements: HW 0.58, HL 0.64, EL 0.16, ON ≈50, MesL 0.66, MesH 0.4, PetAFL 0.26, Ptg3L 0.31, Ptg4L 0.38, TL 2.25. Head. Anterior portion of full-face view of the head and mandibles mostly blocked by an insect antenna which is very close to the ant (could not be removed during specimen preparation). Lateral margins of head straight up to the eye level; from eye posterad, vertexal angles round and poorly defined, vertexal margin strongly convex (head lateral and vertexal margins without clear differentiation from one another). Both compound eyes mostly collapsed and depressed (appearing as they would only be slightly bulging in a preserved condition). Labrum distal margin with one pair of lobes; labral chaetae restricted to basad and mesad areas of labral shield, the distal fringe devoid of them. Hypostomal teeth appearing in anterior view of the head as two lobes laterad the labral lobes. Labio-maxillary complex including all palpomeres completely concealed by the labrum. Dorsal margin of mandible close to apical tooth almost straight. Antennomeres relatively thick and short. Scrobe on the right side of the head clearly visible; unlikely forming a sharp frontal carina (difficult to gauge precisely), most likely a bump on the head dividing the surface from torulus to eye in a medial raised and a lateral depressed levels. Conspicuous setae on the head apparently entirely absent, with only minute pubescence similar to that imaged for the mesosoma ( Fig. 8 , A, C and D, this decumbent pubescence much smaller than the recurved setae on the head of Zigrasimecia ufv-11, see below and Fig. 20 , B). Mesosoma. In profile, mesosomal dorsal outline evenly convex, softly merging into the propodeal posterior margin; still, propodeal posterior surface discernible as a shallowly concave area. In dorsal view, mesosomal lateral margins convex at the pronotal level, tapering along the mesometanotal level, and subparallel along the propodeal level; sclerites on dorsum of mesosoma entirely fused, without lines or sutures to indicate their boundaries. Pronotum width 0.53 x head width. Minute pubescence on dorsum of mesosoma not particularly dense, but neither sparse, without standing setae or recurved conspicuous setae. Propodeal spiracle approximately 0.07 mm, relatively large (about 18% MesH), positioned on mid-height of propodeal lateral surface. Mesosoma in lateral view with the sclerites more easily defined, upper and lower mesopleuron easily-defined and lower metapleuron poorly marked but discernible. Protibia apicoventrally with a pair of simple spur-like setae and the calcar, the latter with a bifid tip and undeveloped velum; on the mesotibia, a pair of simple, subequal spurs and a third, smaller, simple spur; on the metatibia, a simple spur plus a longer and barbulate one. Pretarsal claw with a minute tooth on inner margin; arolia small, about a third the length of the pretarsal claws, present on all pretarsi. Metasoma. In anterodorsal view, anterior surface of petiole node suboval, tip of node arch-shaped; node relatively thick, not anteroposteriorly compressed. In profile view, anterior margin of petiole node oblique, straight to slightly convex, curving evenly into a poorly defined dorsal margin and then to a straight posterior surface which meets a short, ring-like posterior tube. Prora and subpetiolar process interlocked, the shape of both being impossible to precisely describe, although apparently matching the genus diagnosis. Gaster covered on tiny, curved, appressed setae similar to those of the head and mesosoma; devoid of standing setae, except around the sting. Cinctus on dorsal view of the gaster likely moderately developed, but a damage on middle of A4 and A3 tergites makes it difficult to confirm; cinctus difficult to see in lateral view due to distortion created by the corners of the facets.

Comments. The original specimen was a 33 mm x 23 mm x 8 mm polished piece. It contained a lot of debris, an entire mite, a well-preserved small Staphylinidae , a damaged medium-sized beetle (head and pronotum missing), and some fragments of other arthropods, one of which is a long filiform antenna passing right in front of the ant's head. The gaster of the ant was positioned at the edge, with a small portion of the first and second gastral segments damaged. It was isolated from the rest of the piece and is now within a tiny 2.5 mm x 2.2 mm x 2 mm 7-faceted amber block. The filiform insect antenna in front of the ant's head could not be removed and prevents a clear full-face view of the anterior head, blocking most of the antennal insertions, the entire clypeus, and most of the mandibles. The specimen itself has little or no distortion/ stretching and the integument appears intact, except for the compound eyes and maybe a few portions of the frontovertexal area which appear shriveled/sunken.

Zigrasimecia caohuijiae is unlikely the worker caste of Z. tonsora or Z. goldingot , the two species described based on queens (see below under Z. goldingot ), and can be differentiated from Z. boudinoti , Z. chuyangsui and Z. ferox by the lack of standing setae on body. It differs from the most glabrous Z. thate in the absence of a patch of flagellate setae on the frontovertexal area and by the head and mesosoma shape (head subquadrate and propodeal dorsal and posterior surfaces in Z. thate marked by a strong corner and propodeal lobes). It differs from Z. perrichoti by its smaller size, relatively smaller compound eye with fewer ommatidia, and petiole shape.

Etymology. The name is in honor of myrmecologist and paleontologist Huijia Cao. The name was created by adding the singular Latin genitive case suffix -ae to the first and last names of a female person combined. The orthography of an eponym is unchangeable and not dependent on the generic name in which the epithet is used.

Figures

FIGURE 7. Holotype of Zigrasimecia caohuijiae (ANTWEB1041055). A, full-face view of the head (view of anterior portion blocked by an insect antenna and bubbles); B, profile view of right side of body; C, ventrolateral view of anterior portion of head; D and F, anterior view of head, with a full view of dorsal surface of mandibles, F is under epifluorescence; E, dorsal view of the body; G and H, Detail of mesosoma under different types of epifluorescence. Scale bars are 0.2 mm inA, B and E and 0.1 mm in C and D. Black triangles point to the labral medial lobes (laterally to the median lobes in D a pair of protuberances which are likely the hypostomal teeth).Abbreviations: cllb, clypeal lobe; dsm, dorsal surface of mandible; Lmspl, lower mesopleuron; Lmtpl, lower metapleuron; sp, spiracle; Umspl, upper mesopleuron; vsm, ventral surface of mandible.

FIGURE 8. Holotype of Zigrasimecia caohuijiae (ANTWEB1041055). A, dorsal view of mesosoma and petiole; B, detail of the right side of the petiole in profile, white triangle indicates the edge of the sclerite (posterior petiole tube or collar); C, zooming of pronotum in dorsal view under epifluorescent light, black triangles in A and C indicate minute decumbent setae on mesosoma (setae also clear in image D); D, zooming of propodeum and petiole under epifluorescent light; E, posterolateral view of propodeum, black triangle indicates hypertrophied propodeal spiracle; F, detail of probasitarsus, showing concentration of long, fine setae, white triangle indicates calcar with simple tip (not bifid), and black triangle indicates mesopretarsal claws with toothed inner margins; G, inner face of protibia and probasitarsus, showing two spur-like setae next to calcar; H, detail of abdominal segment VII and sting, black triangles show gonostyli. Scale bars are 0.1 mm.

FIGURE 20. Morphospecies Zigrasimecia ufv-11. A and B, head in full-face and anterior views, respectively, of specimen ANTWEB1047053, black triangle indicates curved, decumbent setae on frons and vertex; C, profile view of right side of body of specimen ANTWEB1047903. Scale bar 0.2 mm in A, and 0.5 mm in C.