Zigrasimecia

†Zigrasimecia; Temporal range: Early Cenomanian, Late Cretaceous K Pa Eo Ol Mi Pl Burmese amber, Kachin State, Myanmar
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Formicidae
Subfamily:	Zigrasimeciinae
Genus:	†Zigrasimecia; Barden & Grimaldi, 2013
Type species
	Zigrasimecia tonsora;
Diversity
	10 fossil species; (Species Checklist)

A genus of iron maiden ants, a Formicidae stem lineage with bizarre mouthpart morphology.

Photo Gallery

Identification

Chaul (2023), Fig. 1. Schematic drawings of most of the measurements taken from the specimens (presented in the species descriptions or in Appendix 1). See Materials and Methods or Appendix 1 for a detailed explanation of the measurements. Codes: a, head length; b, head length 2; c, head width; d, head width 2; e, head width 3; f, head maximum depth; g, mesosoma length (see also Fig.6); h, mesosoma height; i, propodeal spiracle length; j, petiole anterior face length; k, posttergite 3 length; o, posttergite 4 length. Measurements a, g, j, k, and o summed equal total length (TL). Gaster measurements l, m, n, and p are additional metasomal measurements that are useful if the measurements k and o are blocked (see Appendix 1).

Chaul (2023), Fig. 3. Comparison between Gerontoformica and Zigrasimecia cephalic and mandibular morphology (see genus diagnosis above for detailed explanation). A and C, schematic drawing of full-face view of Gerontoformica and Zigrasimecia, respectively. B and D, lateral view of anterior head of Gerontoformica (ANTWEB1032649) and Zigrasimecia (ANTWEB1032623), respectively. Abbreviations: cl, clypeus; cllb, clypeal lobe; dsm, dorsal surface of mandible; fcr, frontal carina; plstf, pleurostomal fossa; tl, torulus. In D, white line indicates plane (as seen laterally) of labrum; gray line is the plane (as seen laterally) of the apical half surface of the mandible; and black line shows the strong mandible curvature.
Chaul (2023), Fig. 4. Ventral view of the head of Gerontoformica (A) and Zigrasimecia (B). Abbreviations: cllb, clypeal lobe; dsm, dorsal surface of mandible; lb, labrum; oc, occipital carina; pgs, postgenal suture; plstf, pleurostomal fossa.
Chaul (2023), Fig. 5. Types of mesosoma in fossil and extant ants. A, Gerontoformica; B, Protozigrasimecia; C, Zigrasimecia; D, Brownimecia; E, Brachyponera and F, Discothyrea. Among extant ants, Discothyrea presents a degree of mesosomal compaction similar to that of Zigrasimecia. Abbreviations: Lmspl, lower mesopleuron; Lmtpl, lower metapleuron; mgo, metapleural gland opening; Msn, mesonotum; Mspl, mesopleuron; Mssct, mesoscutum; Mssctl, mesoscutellum; Mtn, metanotum; Ppd, propodeum; Prn, pronotum; Prpl, propleuron, sp, spiracle; Umspl, upper mesopleuron; Umtpl, upper metapleuron.
Chaul (2023), Fig. 14. Relative body size comparison of all described species of Zigrasimecia (with morphospecies Zigrasimecia ufv-11 included, see Section 3.3 of text).

Keys including this Genus

Key to genera of Zigrasimeciinae

Keys to Species in this Genus

Key to Zigrasimecia species

Distribution

This taxon is known from Burmese amber, Kachin State, Myanmar (Early Cenomanian, Late Cretaceous).

Discussion

Cao et al. (2020) - Zigrasimecia was erected based on a single piece of Burmese (Myanmar) amber which contains a dealate gyne, designated as Zigrasimecia tonsora. The unique type specimen was only partially preserved, missing part of petiole and gaster, and details of the mouthparts were difficult to ascertain. The second species of this genus, Zigrasimecia ferox, was described based on the worker caste. Numerous features are shared between Z. ferox and Z. tonsora, although Perrichot (2014: p. 168) adduced a list of specific features which distinguish the two species. The unique morphology of Zigrasimecia is nowhere fully paralleled in the extant Formicidae, and is thought to represent habits that became extinct with the lineage (Barden & Grimaldi 2013).

Conclusion: Our study of Zigrasimecia hoelldobleri and Protozigrasimecia chauli reveals both morphological and functional diversity in stem Formicidae. The holotype of Z. hoelldobleri is shockingly well-preserved for light microscopy, and has yielded insights into mandibular, labral, and clypeal function of the Burmese Zigrasimeciini. Based on the interpreted mouthpart function, we colloquially recognize Zigrasimecia and Protozigrasimecia as the iron maiden ants. Among the Zigrasimeciini, we severely doubt that the monotypic genus Boltonimecia from Canadian amber is correct to include, and recommend revised study. In summary, there are ample opportunities for discovery, characterization, and evolutionary analyses of the Zigrasimeciini, which we have attempted to facilitate through the present work.

Castes

There is a diagnosis of this alate but it has not been assigned to a species.

Cao et al. 2020. Figure 3. Alate gyne of the unplaced Zigrasimecia, No. CNU-HYM-MA2019055; scale bars for (A), (B) = 0.5mm, for (C) = 0.2mm, and for (D) - (E) = 0.5mm. (A), Photograph of alate gyne in lateral view, (B), reconstructive drawing of alate gyne, (C), head of alate gyne in dorsal view, (D) and (E), venation reconstructions, where (D), indicates cells and (E), indicates veins.

Undescribed Species

The following species are included in the revision by Chaul (2023) but not formally described.

Chaul (2023), Fig. 15. Morphospecies Zigrasimecia ufv-04 (specimen ANTWEB1038932). A, head in full-face view; B, profile of right side of body; C, detail of mandibles and clypeus, black triangles indicate clubbed setae on gena; D, posterodorsolateral view of mesosoma and head; E, phoretic mite on mesotibia, with a simplified scheme below the image. Scale bars are 0.2 mm in A, B and D and 0.05 mm in E.
Chaul (2023), Fig. 16. Morphospecies Zigrasimecia ufv-06 (specimen ANTWEB1032645). A, profile of right side of body; B, left side of petiole in dorsolateral view; C, meso- and metatibiae (upper and lower portions of image, respectively), evincing thickened, truncate pilosity. Scale bars are 0.2 mm.
Chaul (2023), Fig. 17. Morphospecies Zigrasimecia ufv-08, two specimens originally in the same piece (separated for study). Specimen UFV-LABECOL-010580 in A, C and D and specimen UFV-LABECOL-010579 in B. A, full-face view of head; B, profile of left side of body; C, zooming of left side of metasoma in profile; D, detail of mesosoma in dorsal view. Scale bars are 0.2 mm.
Chaul (2023), Fig. 18. Morphospecies Zigrasimecia ufv-09 (specimen ANTWEB1047064). A, head in full-face view; B, profile of left side of body; C, anterior (slightly dorsal) view of mouthparts; D, zoom of propodeum, petiole and first gastral tergite, evincing filiform setae on body.
Chaul (2023), Fig. 19. Morphospecies Zigrasimecia ufv-10 (specimen ANTWEB1047051). A, anterolateral view of right side of body; B. Zoom of head and mesosoma of same view of A, black triangle indicates putative promesonotal suture. Scale bar is 0.5 mm in A and 0.2 mm in B.
Chaul (2023), Fig. 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.

Nomenclature

The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

†ZIGRASIMECIA [†Zigrasimeciinae]
- †Zigrasimecia Barden & Grimaldi, 2013: 407. Type-species: †Zigrasimecia tonsora, by original designation.

Taxonomic history

†Zigrasimecia in †Sphecomyrminae: Barden & Grimaldi, 2013: 410.
†Zigrasimecia in †Sphecomyrminae, †Sphecomyrmini: Perrichot, 2014: 166.
†Zigrasimecia in †Sphecomyrminae, †Zigrasimeciini: Borysenko, 2017: 18.
†Zigrasimecia as genus: all authors.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Cao et al. (2020) - Emended diagnosis (female): Distinguished from both Boltonimecia and Protozigrasimecia as outlined in the key above. Sharing uniquely with Protozigrasimecia the large, dome-shaped head with deep and broadly concave occiput in posterior view, and evenly and broadly concave, arcuate clypeus. Additional definition provided by the following characters: antenna of worker and alate gyne 12-merous (see Note 5); worker body length 1.8 - 4.6 mm, gyne body length 2.7 - 4.0 mm; head massive, nearly as large as mesosoma; frontal carinae present; clypeus in form of an evenly arched transverse bar; anterior margin concave with dozens of denticulate traction setae; labrum with dense spiniform traction setae; inner surface of mandibles with traction setae distributed along their length; worker eyes small and rounded; scape at least twice length of pedicel; labrum covered with erect and strong spiniform traction setae; labrum apicomedially bilobate; mesosoma strongly convex and anteroposteriorly compact, without external indication of segmental articulation; helcium (= articulatory sclerites of abdominal segment III) axial (situated at segment midheight). Gyne: most of characters similar with workers, except for the following: eyes reniform; mesoscutum and mesoscutellum demarcated by sulcus; mesosoma musculated for flight; forewing with seven closed cells: the costal, two submarginal, one marginal, the basal, subbasal, and first discal.

Note 6: The antennomere counts of alate Boltonimecia and Protozigrasimecia are unknown.

Note 7: The coronal rugosities described on the vertexal area of the holotype of Z. tonsora are almost certainly artefacts derived from the taphonomic process (BEB, pers. obs., American Museum of Natural History). The rugosities are asymmetrical, and similar apparent bubble streaks can be observed on other, distantly related taxa.

References