Plesiomyrmex, Dlussky & Radchenko, 2009

Dlussky, Gennady M. & Radchenko, Alexander G., 2009, Two new primitive ant genera from the late Eocene European ambers, Acta Palaeontologica Polonica 54 (3), pp. 435-441 : 437

Genus Plesiomyrmex nov.

Etymology: After Greek plesios —close, similar, which means in biological terminology prior, initial, and myrmecos —ant.

Type species: Plesiomyrmex tubulatus sp. nov., by monotypy.

Diagnosis.— Palp formula 6, 4. Antennae 13−segmented, having no apical club, inserted into head close to the posterior margin of the clypeus, however, the nature of the insertions is unusual: toruli are on the tops of short sub−vertical tube−like or cup−like structures that distinctly project above the head surface; scape very short, shorter than each of the 2 nd to 12 th funicular segments. The first funicular segment not globular, ca. 1.2 times longer than broad, subsequent segments elongated, ca. 3–3.3 times longer than broad; segment’s length somewhat increased from 2 nd to 5 th, and then their length gradually decreased to the 11 th segment, apical one is the longest. Frontal triangle is absent. Clypeus does not insert posteriorly between frontal carinae, its median portion elevated, distinctly raised over level of the rest of clypeal surface (seen in profile). Scutum with Mayrian furrows, propodeum angulated, with very short blunt tubercles. Middle and hind tibiae with a big, distinctly pectinate spur, pretarsal claws simple. Mandibles elongate−triangular, with distinct masticatory margin, which has seven small sharp teeth. Forewing with closed cells 1+2r, rm, and mcu. Cell 3r is opened at the apex. Vein section 1RS is vertical, merging with vein R at a right angle. Cross−vein 2r+rs distinctly declined in respect to vein RS. Cross−veins 2r+rs and rs−m coincide on vein RS (vein section 4RS is absent). Cell rm is triangular (vein section 2M is absent), with distinct short stem. Cell mcu is trapezoid, reaching the level of pterostigmal base. Cross−vein cu−a displaced proximally, so that vein section 2M+ Cu is long, much longer than the cross−vein cu−a, as usual in Myrmicinae . Cell cua is absent, vein sections 1 Cu and 2 Cu forming more or less straight line, section 2 Cu does not angulate distally and does not confluent with vein A. Hind wing without vein sections 1M and 2M.

Remarks.—We place Plesiomyrmex in the tribe Myrmicini based on the general shape of the mesosoma, the presence of Mayrian furrows on the scutum, 6−segmented maxillary and 4−segmented labial palps, middle and hind tibiae with a well developed pectinate spur, and the antennal structure. However, the wing venation in Plesiomyrmex is more primitive than in any known Myrmicini genera (see also Discussion below). Plesiomyrmex well differs from all extant genera of Myrmicini by its wing venation, by the structure of funiculus, and by the peculiar character of the antennal insertions.