Pherhombus parvulus, Meier & Wacker & Klopfstein, 2022

Meier, Noah, Wacker, Anina & Klopfstein, Seraina, 2022, New fossil wasp species from the earliest Eocene Fur Formation has its closest relatives in late Eocene ambers (Hymenoptera, Ichneumonidae, Pherhombinae), Bulletin of the SSB (8427) 1 (1), pp. 1-17 : 8-10

Pherhombus parvulus n. sp.

Figure 3

Material. Holotype, #10652 , part and counterpart; sex unknown. Part and counterpart about equally informative, often showing complementary structures (e.g., first tergite). Collector: Jan Verkleij. Deposited at Fur Museum, Nederby.

Type horizon and locality. The fossil was found in Denmark, MorsØ Kommune , Ejerslev in cement stone which has a geological ageof about 54 Ma (early Eocene).

Etymology. In Latin, “ parvulus ” is the diminutive of “parvus” which means small or tiny. This refers to the fact that the fossil species is only 3.3 mm long, which is about half the size of all other described Pherhombinae .

Diagnosis.

Taxonomic placement. Due to the nearly complete preservation of the forewing venation, this species can be placed within the Ichneumonidae with certainty, whichare distinguished from the related Braconidae by lacking vein 1-Rs+M (sometimes with the exception of a short remain, called ramulus) and by the presence of 2m-cu. The rhombic aerolet is probably the most conspicuous charactervisiblein this fossil; itis onlyshared bymembersof thesubfamilies Mesochorinae and Pherhombinae . Several characters, such as the low number of antennal segments, the forewing 1-M+1-Rs to r-rs ratio, the hindwing 1-Rs to rs-m ratio, and the elongated and parallel-sided first tergite, give evidence for the placement within the monotypic Pherhombinae . Even though the new species was placed with the highest probability as a stem representative, there is currently not sufficient morphological evidence that this species should be placed withina new genus. This placement is supported both by the morphometric and Bayesian phylogenetic analyses ( Fig. 1 and 2 ).

Species diagnosis. This species is very similar both in wing venation and shape of the first tergite to many species of Pherhombus . Nevertheless, it can be easily distinguished from all currently described species by its small size (body length: 3.3 mm, forewing length: 2.9 mm), with all other Pherhombus species ranging in body length from 6.7 to more than 9 mm and forewing length from 4.7 to 9.5 mm ( Tolkanitz et al. 2005; Manukyan 2019). It is further distinguished from most other species by the parallel-sided antennal segments, which are otherwise widened towards the apex in all species except perhaps P. kraxtepellensis and P. kasparyani ( Manukyan, 2019), whose antennae are widest around the 8th or 9th flagellomere and only slightly expanded apically. The new species can be distinguished from these two by the presence of a distinct ramulus and by the hyaline wings (smoky in P. kasparyani).

Description.

Preservation. Dorsalview. Headonlypartially preserved, antennae nearly complete with partly clear segmentation. Mesosoma not well preserved, hardly any characters visible except possible hind border of mesoscutum; wings stretched out flat, all four wings nearly complete; partial mid and hind legs visible. Metasoma anteriorly almost complete but segmentation posteriorly unclear; posterior part of metasoma ending abruptly or incomplete, genitalia not visible.

Body 3.3 mm; fossil in different shades of brown; strongly sclerotized parts, such as head or first tergite, distinctly darker than rest, wings hyaline.

Head deformed, no detailed structures distinguishable. Antenna slender, with about 20 flagellomeres (+/- 3); scape and pedicel of normal dimensions (as far as visible), first flagellomere almost 7.0 times longer than apically wide.

Mesosoma rather short and stout; triangular dark patches at forewing base probably corresponding to axial sclerites. Forewing 2.9 mm; areolet closed, rhombic, 3r-m with a bulla at posterior end; 4-Rs straight; ramulus present, slightly longer than width of surrounding veins; pterostigma 4.5 x longer than wide; radial cell 3 x longer than wide; 1cu-a meeting M+Cu opposite 1-M&1-RS; 2m-cu nearly straight, somewhat inclivous, probably with a single large bulla in anterior third or half; 3-Cu about 0.75 x as long as 2cu-a. Hindwing 1-Rs 0.47 x as long as rs-m; 2-Rs tubular on entire length (not counting last 10%); 1-Cu clearly shorter than cu-a. Mid leg very slender, both coxa, femur and parts of tibia and tarsus visible. Hind leg with very long coxa, at least 2.1 x longer than wide; both femur and parts of tibia preserved, femur rather elongated, more than 5.0 x longer than wide.

Metasoma appearing somewhat clubshaped, with widest part close to posterior end; tergite 1 slightly more than 4 x longer than wide, narrow and parallel sided; tergite 2 transverse, 0.75 x as long as wide. Posterior metasomal segments appear truncated, lack of ovipositorsuggests a male, but incomplete preservation also possible.

Figures

Figure 1. Wings of representatives of two candidate subfamilies (a, b) and of the new fossil species (c), combined with morphometric analysis of potential placements. (a) Wing venation of Astiphromma albitarse (Brischke), including vein names as used in this study; (b) wing venation of Pherhombus antennalis Kasparyan; (c) wing venation of Pherhombus parvulus n. sp. as reconstructed; (d) scatterplot of two measurement ratios, forewing veins 1-M+1-Rs / r-rs and hindwing veins 1-Rs / rs-m. The new fossil species groups together with Pherhombinae.

Figure 2. Bayesian phylogenetic analysis of combined morphological and molecular dataset, including RoguePlot showing probability of placement of Pherhombus parvulus n. sp. Branch colours represent posterior probabilities of attachment of the fossil to a particular branch, and support values next to nodes indicate posterior probabilities. The three-letter code in front of the taxon names denotes subfamily affiliation as follows: ACA Acaenitinae, ANO Anomaloninae, BAN Banchinae, BRA Brachycyrtinae, CAM Campopleginae, COL Collyriinae, CRE Cremastinae, CRY Cryptinae, CTE Ctenopelmatinae, CYL Cylloceriinae, DIA Diacriti- nae, DIP Diplazontinae, EUC Eucerotinae, HYB Hybrizontinae, ICH Ichneumoninae, LAB Labeninae, LYC Lycorininae, MES Mesochorinae, MET Metopiinae, OPH Ophioninae, ORP Orthopelmatinae, ORT Orthocentrinae, PHY Phygadeuontinae, PHE Pherhombinae, PIM Pimplinae, POE Poemeniinae, RHY Rhyssinae, TER Tersilochinae, TOW Townesitinae, TRY Tryphoninae, XOR Xoridinae.

Figure 3. Pherhombus parvulus (holotype), microscope image of part 10652_A (left); interpretative drawing based on part and counterpart (right; a photograph of the counterpart is provided as Supplementary File S4). Solid lines imply a high certainty of interpretations, while dotted lines indicate interpolations or uncertain interpretations. Hindwings are shown in green to improve clarity. Differences in line width are used to visualise small structures and do not imply varying certainty. The scale bar indicates 1 mm.