Eotriadomeroides Huber, 2023

Huber, John T. & Greenwalt, Dale E., 2023, A new compression fossil, Eotriadomeroides abjunctus Huber, gen. & sp. nov. (Hymenoptera, Mymaridae), in Eocene shale from the Kishenehn Formation, USA, Journal of Hymenoptera Research 96, pp. 657-666 : 657

Eotriadomeroides Huber gen. nov.

Figs 1-2 , 3-5 , 6, 7 , 8

Type species.

Eotriadomeroides abjunctus Huber, here designated.

Diagnosis.

Female. Antenna with funicle 8-segmented and clava 1-segmented (Figs 2 - 5 ); fore wing with venation extending almost to wing apex, with postmarginal vein as wide as marginal vein or parastigma and ~2.7 × as long as parastigma + marginal + stigmal veins (Fig. 7 ); tarsi 5-segmented (Fig. 8 ); fore wing microtrichia apparently extending to base of parastigma; hind wing relatively narrow, with acute apex; ovipositor extending ventral to mesosoma almost to level of head and not exserted posterior to apex of gaster (Fig. 1 ). Other details are apparently the same as for Neotriadomerus Huber, morphologically the genus most similar to Eotriadomeroides .

Male. Unknown.

Derivation of genus name.

From the Greek, eos, meaning early + Triadomerus (a compound word derived from Greek, tries, meaning three, and meros, meaning part, referring to the 3-segmented clava) + the suffix - oides, meaning like, resembling. Eotriadomeroides (gender masculine) is therefore an "early Triadomerus -like" genus, referring to its geological age (the Eocene) and morphological similarity to the two other, evidently related genera: Neotriadomerus (with all its species extant) and Triadomerus (with its single species extinct).

Relationships.

Genera of Mymaridae are usually divided formally into subgenera if females of different species within a given genus have either a 1- or 2-segmented clava, or either a 2- or 3-segmented clava, and the other morphological features are essentially identical. So far, no genus is known to have its included species with either a 1-segmented or a 3-segmented clava but none with a 2-segmented clava. Only one genus ( Anaphes Haliday) possibly has its included species with a 1-, 2-, or 3-segmented clava but so far Anaphes species with 3-segmented clava have yet been described and named. Examination of the clava of Eotriadomeroides does not suggest it is 2- or 3-segmented but rather that it is clearly 1-segmented, i.e., entire (Fig. 5 ). For comparison, the species of Eoanaphes Huber and Eoeustochus Huber from the same formation and apparently with the same quality of preservation, are clearly 3-segmented whereas those of Gonatocerus Nees are just as clearly 1-segmented ( Huber and Greenwalt 2011). If the clava of E. abjunctus were 2- or 3-segmented then it could be classified as a subgenus of Neotriadomerus , given that all other features, except relative lengths of postmarginal vein to the rest of the venation, are almost the same in both taxa. Eotriadomeroides would then key to Neotriadomerus in the key to Cretaceous genera of Mymaridae ( Poinar and Huber 2011). Another possibility would be to treat E. abjunctus as a subgenus within Triadomerus Yoshimoto, described from amber from Cedar Lake, Manitoba ( Yoshimoto 1975), which is only about 1000 km away from the type locality (the Kishenehn Basin, Montana) of E. abjunctus . According to McAlpine and Martin (1969) the actual source of the Cedar Lake amber is more likely to be upstream, along the Saskatoon River either near Saskatoon, Saskatchewan, or Medicine Hat, Alberta, respectively about 650 km and ~280 km from the type locality of E. abjunctus as determined from the present day configuration of the localities (essentially unchanged from 46 my years ago). Triadomerus does not have the ovipositor extending anteriorly ventral to the mesosoma and it has a relatively short postmarginal vein compared to length of stigma + marginal + parastigmal veins, so we treat E. abjunctus as belonging to a new genus, different from both Neotriadomerus and Triadomerus , both of which have a 3-segmented female clava and are known, respectively, from seven extant and one extinct species. Eotriadomeroides is best classified in Triadomerini ( Huber 2017) but exact relationships among the genera still need resolution.

Figures

Figures 1, 2. Eotriadomeroides abjunctus Huber, holotype female 1 habitus (except most legs not visible) 2 pronotum + head + partly disarticulated antennae.

Figures 3 - 5. Eotriadomeroides abjunctus Huber, holotype female 3 head + part of antennae 4 left antenna (pedicel-fu 5) 5 fu 8 + clava of both antennae.

Figures 6, 7. Eotriadomeroides abjunctus Huber, holotype female 6 mesosoma 7 wings + metasoma.

Figures 8, 9. Eotriadomeroides abjunctus Huber, holotype female 8 tibiae and tarsi of one? pair of legs 9 shale piece containing holotype (circled) of Eotriadomeroides abjunctus Huber.