Eocenomyrma groehni, Radchenko, 2020

Radchenko, A., 2020, New Species Of Extinct Ant Genus Eocenomyrma Dlussky Et Radchenko (Hymenoptera: Formicidae: Myrmicinae) From The Baltic Amber, Annales Zoologici 70 (1), pp. 109-111 : 110

Eocenomyrma groehni sp. nov.

= Eocenomyrma orthospina: Radchenko and Dlussky 2016: 407 (only specimen No. 6800, misidentification, nec Dlussky and Radchenko, 2006: 563).

Locality. Baltic amber, Late Eocene, Priabonian stage, 33.9–37.8 Ma.

Description. Worker. Total length ca. 2.7 mm. Head somewhat longer than wide, with slightly convex sides, widely rounded occipital corners and slightly concave occipital margin. Eyes relatively big, situated somewhat in front of sides of head. Frontal carinae moderately curved, frons quite wide; they merging with rugae that extend to occipital margin, do not curve outwards and do not merge with rugae that surround antennal sockets; frontal lobes extended laterally, covered base of antennae. Anterior clypeal margin widely and shallowly concave medially. Antennae 12-segmented, with rather big 3-segmented apical club that subequal to total length of remainder funicular segments; scape quite long, almost reaching occipital margin, smoothly curved at base, without lobe or carina. Shape of mandibles barely visible.

Mesosoma quite slender, twice longer than pronotal width, humeri rounded, promesonotal suture absent, propodeal groove deep. Propodeal spines long, straight and acute, ca. 0.5 times of head width, strongly divergent (seen from above). Petiole with long peduncle, anterior surface of its node strongly concave, node quite high, with rounded dorsum. Postpetiole wide, ca. 1.4 times of its own length and ca. 1.3 times of width of petiole. Spurs on middle and hind tibia obscured.

Whole head dorsum with slightly sinuous longitudinal rugae. Mesosomal dorsum with coarse reticulation, only surface between propodeal spines with fine transversal rugosity; petiole, postpetiole and gaster smooth and shiny. Surface between rugae on head and mesosoma with fine superficial punctation, but appears shiny.

Temples and occipital margin of head with a few straight, quite long and thin erect to suberect hairs, mesosoma with sparse hairs, waist and gaster with more abundant similar hairs. Antennal scape and legs with decumbent to subdecumbent pilosity. Body colour dark brown.

Measurements (in mm) and ratios: HL 0.66, HW 0.60, SL 0.41, FW 0.25, FLW 0.30, OL 0.14, ML 0.75, PNW 0.38, PL 0.31, PW 0.23, PPL 0.21, PPW 0.29, HTL 0.43, ESL 0.29, ESD 0.30;

HL/HW 1.11, SL/HL 0.69, SL/HW 0.76, FW/HW 0.41, FLW/FW 1.21, OL/HL 0.22, ML/PNW 2.00, PL/HW 0.52, PW/HW 0.39, PPW/PW 1.28, PPW/HW 0.50, PPW/PPL 1.44, ESL/HW 0.48, ESD/ESL 1.05.

Queens and males. Unknown.

Type material. Holotype worker, complete specimen, GPIH No. 4945, coll. Gröhn No. 6800 (AntWeb CASENT No. 0917556).

Etymology. The species is dedicated to Mr. Carsten Gröhn, who collected the holotype specimen.

Remarks. Among all known Eocenomyrma species, E. groehni may be confused only with E. orthospina Dlussky et Radchenko, 2006 , but it well differs from the latter species by structure of the frontal carinae, which merging with the rugae that extend to the occipital margin; in contrary, the frontal carinae in E. orthospina are short, curve outwards and merge with the rugae, which surround antennal sockets. Additionally, entire head dorsum in E. groehni is with the slightly sinuous longitudinal rugae, but in E. orthospina the only frons is with the not coarse longitudinal, slightly sinuous rugae, and the lateral parts of the head dorsum and occiput are with reticulation.

Figures

Fig. 1. Eocenomyrma groehni sp. nov., holotype worker, photos of the details of structure: (A) body, dorsal view; (B) – head, dorsal view.