Zigrasimecia hoelldobleri

†Zigrasimecia hoelldobleri; 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
Species:	†Z. hoelldobleri
Binomial name
	†Zigrasimecia hoelldobleri; Cao, Boudinot & Gao, 2020

The well preserved holotype of this species has provided an opportunity to study Zigrasimeciini mandibular, labral, and clypeal form and function.

Identification

Cao et al. (2020) - Worker. Differs from Zigrasimecia tonsora as follows: (1) apical concavity of mandible, subtending distal tooth on the external surface, less pronounced; (2) basal mandibular margin distinctly but shallowly convex along its length to the basal tooth, rather than being more-or-less linear to its apex; (3) one long seta situated on ventral mandibular margin, about 2/3 length of mandible (versus several; single seta state shared with Zigrasimecia ferox); (4) labral traction setae stouter; (5) clypeus with > 30 traction setae; (6) face just posterad posterior clypeal margin without paired transverse sulci; (7) body (head, mesosoma, metasoma) with more-or-less even layer of long erect setae (versus setae much shorter, stubblier); (8) propodeum without median longitudinal groove. Differs from Z. ferox as follows: (1) numerous long erect setae present in malar space of head (versus absent); (2) scape relatively longer (SI [SL / HW] = 0.44 vs. ~ 0.29 - 0.39); (3) foretibia with single spur-like seta posterad calcar; (4) mesosoma evenly arched, propodeum without distinct dorsal and posterior faces (versus mesosoma with dorsal propodeal face angled relative to mesonotum and posterior propodeal face); and (5) body setation longer, denser. Identification supported by the following conditions which are not necessarily unique among Zigrasimecia species: (1) entire body covered with long and erect setae; (2) body length ranging from 2.6mm to 3.5mm; (3) labrum bilobed, with a distinct median notch; (4) eyes small and elliptical to circular; (5) ocelli absent; (6) scape to flagellomeres I or III covered with long and erect setae; (7) antennomeres sequentially and gradually shorter toward antenna apex; (8) anterior labral margin with a row of cincinate (curved) setae; (9) mandible weakly bidentate, with two small denticles; (10) apex of subapical mandibular denticle aligning with apical denticle; and (11) oral face of mandible with 3 rows of erect spiniform setae.

Chaul (2023) - Large species. Head subquadrate in full-face view. Body pilosity composed of long, flexuous, mildly clavate, and apically truncate setae. Labral distal margin fringed with soft setae. Dorsal mesosomal outline conspicuously convex; propodeum without strongly marked corners between the dorsal and posterior surfaces. Petiolar node apex brief, but not sharp, the transition from the anterior to the posterior surfaces being a short, curved surface.

The holotype of this species is very distinct for its pilosity and large size (Fig. 14), being easily separated from all remaining species of Zigrasimecia by those respects. Two morphospecies are similar to Z. hoelldobleri, however their poor preservation prevents any conclusive identification. See comments under morphospecies Zigrasimecia ufv-04 about a possible complex of species formed by it, Z. hoelldobleri and Zigrasimecia ufv-06.

The paratype CNU-HYM-MA2019054 of Z. hoelldobleri, differs considerably from the holotype and is here taken out of the type series of the species for not sharing the same type of setation with the holotype. Moreover, CNU-HYM-MA2019054 propodeum appears to have better-defined faces and the petiolar node with better defined top and posterior faces. The specimen is probably conspecific to specimen CNU-HYM-MA2019065, both are likely members of a new species similar to Zigrasimecia ferox, but differing from the latter by having somewhat longer and more abundant pilosity on the body, the apex of the node oblique rather than flat, and a slightly different shape of the head, with the anterior section just posterad the clypeal lobes a bit more constricted (see comments about specimen CNUHYM-MA2019065 below). Alternatively, the limits of Z. ferox could be broadened to include specimens CNUHYM-MA2019065 and CNU-HYM-MA2019054, something that should preferably be done when more specimens are available and/or can be physically examined.

The distalmost row of very thin, crooked setae on the labrum of Z. hoelldobleri holotype is an odd and unique trait of the species; however, it is difficult to check in specimens with a retracted labrum (most of the known specimens so far); therefore, it could be, in fact, a more common trait in the genus.

Keys including this Species

Key to Zigrasimecia species

Distribution

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

Castes

Cao et al. 2020. Figure 1. Worker of Zigrasimecia hoelldobleri, holotype, No. CNU-HYM-MA2019053; scale bars for (A), (B) = 0.5mm, for (C) - (E) = 0.2mm. (A) photograph of worker in lateral view; (B) line drawing; (C) detail of the mouthparts; (D) photograph of head in dorsal view; (E) line drawing of head. Abbreviations: at, apical tooth; cd, clypeal denticles; ga, galea; gl, glossa; lt, labral tubercle; mp, maxillary palpus; ms, mandibular spicules; ls, long seta on outer surface of mandibles; sat, subapical tooth. Traction setae = cd, lt, ms.

Cao et al. 2020. Figure 2. Photograph of worker of Zigrasimecia hoelldobleri, paratype, No. CNU-HYM-MA2019054; scale bar for (A) = 0.5mm, for (B) = 0.2mm, for (C) = 0.25mm, and for (D) = 0.1mm. (A) photograph of profile in dorsal view; (B) profile in lateral view; (C), petiole of paratype; (D) head in full face view.

Nomenclature

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

†hoelldobleri. †Zigrasimecia hoelldobleri Cao, Boudinot & Gao, 2020: 164, figs. 1-3 (w.) MYANMAR (Burmese amber).

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

Description

Worker

Measurements (in millimeters) for holotype (No. CNU-HYM-MA2019053) and paratype (No. CNU-HYM-MA2019054, in brackets [ ]) specimens: Body length 3.53 [2.6]; head length (from vertex to clypeal margin) 0.8 [0.55], width (excluding eyes) 0.9 [0.5]; eyes diameter 0.2 [0.14]; total length of antenna 1.87 [1.11], scape 0.40 [0.12], pedicel 0.15 [0.07], flagellomeres I - X 0.17, 0.15, 0.12, 0.12, 0.12, 0.10, 0.10, 0.10, 0.10, 0.20 [0.12, 0.09, 0.09, 0.09, 0.08, 0.08, 0.07, 0.08, 0.08, 0.15], respectively; maxillary palp: 0.16, 0.12, 0.07, 0.04, 0.03, 0.05, respectively; labral palpomeres I - V: 0.04, 0.04, 0.04, 0.05, 0.07, respectively; mesosomal length 1.25 [0.57], maximum height [0.35]. Legs: forefemur 0.64, mesofemur 0.61, metafemur 0.73; protibia 0.52 in length; mid tibia 0.51 in length; hind tibia 0.62 in length. Petiole length [0.3], height (including subpetiolar process) ~ 0.4; [0.34]. Gastral length (excluding sting): gaster comprising segments III - VII of seven segments exposed of holotype: 0.6, 0.34, 0.18, 0.18, 0.16; total length [1.2] of paratype, sting [0.04].

Holotype No. CNU-HYM-MA2019053; Paratype, No. CNU-HYM-MA2019054, characters of paratype differing from holotype are described in brackets. Whole body covered with long, erect setae; many of the setae clavate [pointed, setae sharp at apex]; setae denser on legs, shorter and fewer on antennal flagellum.

Head: broad [In lateral view, head triangular; frons and lower face forming a plane]. Eyes bulging. Ocelli absent. Antenna with 12 antennomeres. Scape, pedicel as well as flagellomeres I - III covered with a few erect setae on ventral surface, which is shortening in each antennomere. Frontal carinae present between antennae, extending posterolaterally from posterior clypeal margin to anteromedian eye margin, carinae forming posterior margin of short, shallow scrobe. Clypeus curved across its length; lateralmost portions of clypeus, dorsal to mandibular insertion, expanded as disc-shaped lobes; anterior clypeal margin slightly emarginate medially; anterior clypeal margin with at least 48 [34] peg-shaped denticles arranged in a single row. Labrum large, filling most of oral area; distalmost margin covered with a row of short, crooked setae; distal margin with median slit-like cleft; at least 30 [54] suberect spiniform setae present across labral disc; these setae somewhat cone-shaped, with the proximalmost row relatively shorter and thinner. Mandibles with three rows of stiff and spicule-like setae along basal margin; these setae of three different level lengths, the outermost row shortest and the innermost row longest; apex of subapical tooth aligning with apical tooth; both teeth of masticatory margin short, being subequal in length to clypeal traction; a single long seta present on outer mandibular surface. Maxillary palp 6-merous, with erect setae.

Mesosoma: very compact, with dorsal margin evenly convex in lateral view; dorsal lines between each sclerite completely effaced. Mesothorax narrow; metathorax and propodeum in profile with dorsum distinctly rounded [paratype: posterior flange of propodeum forms an angle that is slightly smaller than 90°]; propodeal spiracle slit-shaped. Tibial spur formula 2s, 2(1s,1p); protibia with single spiniform seta posterior to calcar; pectinate metatibial spur large relative to simple spur, which is also subtended by a spiniform seta. Probasitarsus covered with patch of dense setae on ventral surface. Pretarsal claws dentate. Apicomedian lobate setae (plantar lobes) on ventral apex of tarsomeres I - IV absent.

Abdomen with seven exposed segments. Petiolar node squamiform (compressed anteroposteriorly); vertex of petiolar node medially emarginate [for paratype: ventral surface of petiole even, subpetiolar process presence uncertain]. Helcium short. Gaster five segments. Gastral tergum I evenly convex to posterior margin; posterior margins of tergum and sternum I not cinched, that is, not having posteriorly-directed surfaces. Gastral segment II without defined cinctus [for paratype, the second gastral segment distinctly larger; sternite of gastral segment V larger than tergite, connected with tergite closely, gradually narrowing to apex, slightly upcurved apically]. Sting short but stout, largely internalized and only an element of sting exposed.

Type Material

Holotype: No. CNU-HYM-MA2019053, worker; Paratype: No. CNU-HYM-MA2019054, worker. Kachin (Hukawng Valley) of northern Myanmar. The lowermost Cenomanian (near Albian boundary).

Burmese amber, Noije Bum hill, some 18 km southwest of Tanai Village (26°21′33.41″N 96°43′11.88″E / 26.3592806°N 96.7199667°E / 26.3592806; 96.7199667) in the Hukawng Valley, of northern Myanmar. Depository: Key Lab of Insect Evolution and Environmental Changes, College of Life Sciences, Capital Normal University (CNU), Beijing, China.

Etymology

The specific name is in honor of myrmecologist Dr. Bert Hölldobler, for his outstanding contributions on studying evolution and social organization in ants.

References