Zigrasimecia sinusoidal, Zhuang & Jouault & Perrichot & Wang & Liu & Zhang, 2025

Zigrasimecia sinusoidal sp.nov.

Etymology: This specimen is named after the stringy wrinkles on its abdomen.

Material: Holotype YKLP-AMB-011, worker.

Type locality and stratigraphy: Noije Bum Hill , Hukawng Valley, Kachin Province, northern Myanmar; upper Albian–lower Cenomanian (~98.79 ± 0.62 Mya) .

Diagnosis: Middle-sized body. Head flat. Frontal carinae extending to the anterior margin of the eyes. Clypeus extremely narrow in the middle. Mandibles thin, sickle-shaped. Propleuron convex, oval. Abdomen covered with densely wrinkled microsculptures.

Description: Holotype worker ( Figs 3, 4). Measurements (Length and width in millimetres): HWed, 0.63; HWev, 0.68; HL, 0.67; EWI, 0.12; ON, ~100; HD, 0.40; ML, 0.74; PetAFL, 0.37; Ptg3L, 0.56; Ptg3H, 0.26; Ptg4L, 0.61; PnLi, 0.41; PnWa, 0.41; TL, 2.94; MnL, 0.30; HPI, 0.63; HSI, 0.86; Ptg3I, 2.14.

Head: In front view, top of head wider than bottom, densely covered with short setae. Compound eyes flat and round, ~100 ommatidia. Ocelli absent. Frontal carinae deep, obviously raised and develop to compound eyes on both sides. Antennae fossa round, shallow, base large. Antenna with 12 flagellomeres; there also some bubbles wrapped around the surface. Scape wide, longest in all flagellomeres. Flagellomeres II–XI flat, gradually shorter in sequence. Twelfth flagellomere slightly longer than flagellomere II–XI, but narrower. All flagellomeres developed slightly longitudinal microsculptures, distinguished by optical texture from bubbles. Clypeus extremely narrow in the middle, clypeal denticles almost adjoining to the most anterior part of frontal carinae, both sides distinctly enlarged, joining mandibular bases. Clypeal denticles cylindrical, short and dense. Labrum large, apicomedially bilobate. Labrum with stubby setae at root. Mandibular tip very thin and narrow, sickle-shaped, developing fine, dense, acicular setae. Maxillary palpomeres, total counted five; and labial palpomeres, total counted three.

Mesosoma: Dense light wrinkling. Dorsal mesosoma sclerites fused and smooth, limit between propodeum and pronotum absent. Pronotum wide, mesonotum narrow and metanotum concave at dorsal side middle. Propleuron convex, oval, margin clear. In lateral view, a distinct half-moon groove forms bottom line of propleuron. Legs distinctively short and stout, more or less wrapped in bubbles. Protibia with long calcar. Pretarsal claw simple, arolia narrow, drop-shaped. Hindleg femoral and tibial segments almost equal in length, densely covered with wrinkle microsculptures.

Metasoma: Petiolar node thick but high, apically slightly concave in middle. Abdomen well developed, with seven segments visible (constriction between AV-AVII exists). Abdominal segments III and IV are significantly larger than the other segments. Abdominal segment III longest in average length, but abdominal segment IV obviously longer in dorsal line of abdomen. Other abdominal segments strongly contracted and difficult to observe. Abdomen with the development of distinctive ripple-like wrinkle microsculptures in lateral view and dorsal view. Sting obscured (also in CT data).

Comments: The frontal carinae are generally present in most Zigrasimecia workers; however, only this species exhibits frontal carinae that are both strongly developed and uniquely shield-shaped along the anterior margin of the head. Additionally, this species is distinguished by an exceptionally narrow clypeus, with the antennal insertions positioned laterally rather than dorsolaterally; a condition not observed in any other congeneric species. Notably, neither the clypeal morphology nor the frontal carinae configuration of this species has been observed in any described female castes (queens or gynes), precluding the identification of a corresponding female at present.

Key to the workers of Zigrasimecia [For a key for Zigrasimecia based on alate females, please refer to Chaul (2023).] Common characteristics of worker ants within this genus are as follows: ocelli absent; without wing or wing remains; mesosoma compact and simplified..................................................................................................................................................................................1

1. Abundant and conspicuous setae on dorsum of body ............................................................................................................................2

- Body smooth, or sparse and not obvious setae ........................................................................................................................................6

2. Setae on body short, tip of petiolar node truncate ...................................................................... Zigrasimecia ferox Perrichot, 2014 View in CoL

- Setae on body long, tip of petiolar node not truncate ........................................................................................................................... 3

3. Setae subflagellate or hook-shaped. Compound eyes small. Tip of petiolar node thick and bilobed ............................................. ...................................................................................................................................................................... Zigrasimecia thate View in CoL Chaul, 2023

- Setae standing and long. Compound eyes relatively big. Tip of petiolar node either round and not bilobed or thin and bilobed ............................................................................................................................................................................................................. 4

4. Setae on body thick, tip of individual seta truncated and sometimes slightly clavate ........................................................................ ..................................................................................................................................................... Zigrasimecia hoelldobleri Cao et al., 2020 View in CoL

- Setae on body thin and filiform 5

5. Mesosoma compact. Frontal carinae shallow. Tip of petiolar node round. Head round in shape in frontal view, with lateral and vertexal margins poorly differentiated. Ommatidia number <100............................. Zigrasimecia chuyangsui View in CoL Chaul, 2023

- Mesosoma not particularly compact. Frontal carinae conspicuous. Tip of petiolar node and bilobed. Head subrectangular in frontal view, with distinct lateral and vertexal margins. Ommatidia number> 150 ........... Zigrasimecia boudinoti View in CoL Chaul, 2023

6. Frontal carinae absent or shallow ............................................................................................................................................................... 7

- Frontal carinae developed and distinctive ................................................................................................................................................8

7. Middle-sized species, TL> 2 mm. Tip of petiole round and not bilobed. Ommatidia number> 30............................................. ............................................................................................................................................................. Zigrasimecia caohuijiae View in CoL Chaul, 2023

- Small-sized species, TL < 2 mm. Tip of petiole bilobed and relatively thick. Ommatidia number <30 ....................................... ............................................................................................................................................................. Zigrasimecia zui Zhuang et al., 2023 View in CoL

8. TL> 3 mm. Regular and hair-like setae developed on both sides of clypeus .............................. Zigrasimecia bellator sp. nov.

- TL < 3 mm. Clypeus smooth ...................................................................................................................................................................... 9

9. Head rectangular in shape in frontal view, length distinctively longer than width. Posterior clypeal margin weakly marked. Clypeus board. Antennae develop above both sides of clypeus.............................................. Zigrasimecia perrichoti View in CoL Chaul, 2023

- Head rectangular in shape in frontal view, width distinctively longer than length. Posterior clypeal margin strongly marked but clypeus narrow. Antennae develop on both sides of clypeus............................................... Zigrasimecia sinusoidal sp. nov.