Firkantus Viertler, Klopfstein & Spasojevic, 2023

Viertler, Alexandra, Urfer, Karin, Schulz, Georg, Klopfstein, Seraina & Spasojevic, Tamara, 2023, Impact of increasing morphological information by micro-CT scanning on the phylogenetic placement of Darwin wasps (Hymenoptera, Ichneumonidae) in amber, Swiss Journal of Palaeontology (30) 142 (1), pp. 1-27 : 14-15

Genus Firkantus Viertler, Klopfstein & Spasojevic gen. nov. (masculine)

urn:lsid:zoobank.org:act:93A7E291-93A0-4278-B40B-51F5092551FD

Etymology: Firkantus is derived from the Danish word “firkant”, meaning rectangle, which indicates the rectangular and square shapes of the areas enclosed by the propodeal carinae.

Type species: Firkantus freddykruegeri gen. et sp. nov. Systematic placement: The general habitus of this specimen resembles Metopiinae , with a slightly convex face, swollen legs, broad first tergite with spiracle around the middle, and broad and short tergites. The clear division of the clypeus from the face, lack of a triangular process on the dorsal part of the face, as well as no visible ridge between the antennal sockets to median ocellus, and complete propodeal carination (all only detectable after the micro-CT scan) precludes a placement in Metopiinae .

With the complete carination on the propodeum, revealed with the micro-CT scanning, the fossil specimen resembles some taxa in the tribe Tryphonini (Tryphoninae) , which sometimes also exhibit a rather stout appearance. Some characters of the fossil, such as the transverse impressed clypeus, stout T 1, and the tergites with a broad transverse groove, are found in Ctenochira Förster, 1855 . What speaks against the placement in Ctenochira , or the tribe Tryphonini in general, are the tapered mandibles, the strongly impressed notauli, the simple tarsal claws of the fossil, vein 1Cu being shorter than cu-a (nervellus intercepted above the middle) on the hind wing and the dorsoventrally depressed aedeagus. The very broad laterotergites do appear in some Tryphonini taxa, but this is rather rare.

The fossil also resembles Pimplinae , in the short and deep pronotum, the wing venation, broad laterotergites, dorsoventrally compressed aedeagus and the overall habitus shape. The complete carination can also be found in a few pimpline genera, Teronia Holmgren, 1859, Xanthopimpla and the extinct genus Crusopimpla Kopylov, Spasojevic & Klopfstein 2018 . Firkantus freddykruegeri gen. et sp. nov. is placed in Pimplinae , which is also in agreement with the phylogenetic placement.

Diagnosis: A placement in the extinct genus Crusopimpla can be excluded because the new fossil genus has the occipital carina present ventrally, its pterostigma not as broad, and 1Cu shorter than cu-a in the hind wing. Also, Crusopimpla species show a rather short 2Cu cell in the fore wing, while our fossil has it 2.6 × as long as wide.

The new fossil genus shares many characteristics with Lissopimpla and Xanthopimpla , such as the strongly tapered mandibles (Character #1), the deep notauli (Character #57), the presence of lateromedian, lateral longitudinal (Character #76) and posterior transverse propodeal carinae (Character #79), the slender and barlike orbiculae on the hind claws (Character #124) and the broad laterotergites on T 2– T 4 (Characters #188, #194 and #198). Xanthopimpla and many Teronia species possess a yellow-coloured body, with usually black spots or stripes on the metasoma. Unfortunately, in our fossil we cannot determine the ground plan coloration or color patterns. Xanthopimpla additionally shares the following characteristics with the fossil specimen: the conspicuously thickened hind femur (Character #110), large tarsal claws (not coded) and nervellus intercepted above the middle (Character #151).

However, our fossil specimen has complete propodeal carination, which is not the case in Lissopimpla, Teronia or Xanthopimpla , which almost always lack the anterior transverse carina, or at least the median portion. Teronia can further be excluded because of their broad mandibles, that are not as strongly tapered, and the short, indistinct, or rather shallow notauli. Other characters that are very typical for Xanthopimpla and Lissopimpla , but are absent in our fossil, are the crest in front of the notauli, eyes with an invagination opposite the antennal sockets in dorsal view, an impunctate and smooth sculpture on T 1, and T 3 with a transverse, lozenge shaped area, bordered by deep grooves, at least posteriorly.

Because of the previously mentioned morphological disagreements with similar genera, which are also reflected in the phylogenetic analysis, we confidently describe a new pimpline genus Firkantus gen. nov.

Description: The new genus Firkantus is characterized by the evenly convex face separated from the clypeus, the clypeus small and the apical margin without tubercles, denticles or prominent protrusions, the strongly tapered mandibles, the malar space shorter than the mandible base width and the occipital carina ventrally present. The mesosoma has deep converging notauli, reaching the middle of the mesoscutum, the propleuron without a lobe, the epicnemical carina not reaching the anterior margin of the mesopleuron, complete propodeal carination, posterior transverse carina of the mesosternum present laterally and between the mid coxae, metapleuron with the juxtacoxal carina present. The new genus has the hind femur enlarged, large claws, with slender and barlike orbiculae. The hind wing has 1Cu shorter than cu-a, and the T 1 is finely punctate and slightly longer than wide, with the glymma present, the laterotergite triangular and membranous with parallel latero-median carina reaching the posterior end, as well as T 2– T 4 creased, with lateromedian round swellings and subapical impressions, and the parameres strongly enlarged and longer than most tergites laterally.