A malar sulcus is found in very few extant platygastrids: Orwellium Johnson, Masner & Musetti, Aleyroctonus Masner & Huggert, Alfredella Masner & Huggert, Metaclisis Förster and Oligomerella Masner & Huggert. In all but Orwellium and Prototeleia, the malar sulcus is bordered by malar and facial striae. The malar area is obscured in the holotype female of P. kleio, but the malar sulcus can be seen in the paratype male (Figure 7).

Figures 4–6. 

Prototeleia kleio, holotype female (CNU-HYM-MA-2017056) 4 head, anterodorsal view 5 wings, anterodorsal view 6 head, mesosoma, metasoma, lateral view of left side.

Figures 7, 8. 

7 Prototeleia kleio, paratype male (OSUC 226542), head, anteroventral view.

Each of the platygastrid genera that have a malar sulcus also have a prespecular sulcus on the dorsal mesopleuron. This sulcus may exist as a line of foveae, as in Aleyroctonus and Metaclisis (Figure 11), or a line of rugae (Figures 15, 16). Given that the trend in Platygastridae is toward reduction of sulci, we consider the presence of the prespecular sulcus to be plesiomorphic.

Figures 9–16. 

9 Nirupama (OSUC 226542), mesosoma, lateral view 16 Prototeleia kleio (CNU-HYM-MA-2017056), mesosoma, lateral view.

We here propose a hypothesis that the transepisternal line in Platygastridae originates from three landmarks surrounding an ancestral femoral depression. Figures 11–16 illustrate these landmarks (a–c) in a transformation series from the putatively derived (Figure 10) to ancestral (Figures 15, 16) states. The first landmark (a) is a depression or ridge on the anteroventral mesopleuron. In O. enigmaticum, P. kleio and Inostemma Haliday it is a simple ridge, whereas in Sacespalus Kieffer it is a curved line of foveae (Figures 13, 14). The foveae in Sacespalus are dorsal to the mesopleural carina and posterior to a raised area at the anterior margin, making them positionally homologous to the subacropleural sulcus in Archaeoteleia Masner (see Figures 7, 8 in Talamas et al. (2017)). The second landmark (b) was interpreted by Johnson et al. (2009) to be the mesopleural pit in O. enigmaticum. We consider that it may be a fovea of the mesepimeral sulcus, which is consistent with its location at the margin of an elevated posterior mesepimeral area (Figure 15). Supporting this idea, Figure 9 illustrates a species of the scelionid genus Nirupama Nixon in which the mesepimeral sulcus is reduced to two foveae. The location of these foveae in Nirupama corresponds to that of the single fovea in both O. enigmaticum (Figure 15) and Inostemma (Figure 12). The third landmark (c) is indicated in O. enigmaticum by a short line of foveae in the posteroventral portion of the mesopleuron, and we hypothesize that these are homologous to the more dorsally located line of foveae in Sacespalus (Figures 13, 14) and the single fovea in Metaclisis (Figure 11). The location of this landmark in Inostemma (Figure 12) and P. kleio (Figure 16) is speculative because no foveae are indicated. The angled form of the transepisternal line in Metaclisis, also found in Alfredella (Lahey et al. 2021), can thus be interpreted as a furrow connecting these three landmarks. In cases where the landmarks are either colinear or further reduced, the transepisternal line becomes a simple furrow as in Fidiobia Ashmead (Figure 10). Implicit in this explanation is the assertion that the dorsomedial fovea (b) in Sacespalus is associated with the mesepimeral ridge. The transepisternal line is found only in Platygastridae and Proterosceliopsidae, and in the latter it terminates posteriorly at the mesepimeral sulcus (see Figure 16 and fig. 53 in Talamas et al. 2019) but is otherwise a rather simple and smooth arc. Analysis of internal anatomy is clearly needed in these taxa to determine if the transepisternal lines are homologous and test our hypothesis about the evolution of this structure.

The presence of a paracoxal sulcus in the ventral portion of the metapleuron is a rarity in Platygastridae. Lahey et al. (2019) reported it to occur only in Calixomeria Lahey & Masner, but it can also be found in some Metaclisis (Figure 11). In these two genera it is a smooth furrow, whereas in Prototeleia it is a line of foveae (Figure 16).

We consider a foveate metanotal trough to be plesiomorphic for Platygastroidea because it occurs in all families and all Cretaceous fossils that we have examined. Secondary modification occurs in some Scelionidae where the metanotal trough is largely smooth (some Telenomus Haliday) or contains a transverse furrow (e.g. Dvivarnus mikuki Talamas & Miko) and in Janzenellidae where the metanotal trough is irregularly rugulose in addition to having foveae present (Bremer et al. 2021). Prototeleia has a foveate metanotal trough (Figures 3, 16), which is also found in number of extant platygastrid genera. The scanning electron micrographs and illustrations in Masner and Huggert (1989), and our own observations indicate that the foveate metanotal trough is found in Allostemma Masner & Huggert, Aphanomerus Perkins, Calomerella Masner & Huggert, Errolium Masner & Huggert, Metaclisis (variable within the genus, Figure 11), Nanomerus Masner & Huggert, Orseta Masner & Huggert, Orwellium (Figure 15), Pseudaphanomerus Szelényi, Proplatygaster Kieffer, Sacespalus (Figure 14) and Zelostemma Masner & Huggert. However, the majority of platygastrid genera have a smooth metanotal trough (Figure 10). The distribution of this character suggests that it may eventually be useful for dividing the family at the tribal or subfamily levels.

Figure 17. 

Prototeleia kleio, paratype male (OPPC-BUR-1719), lateral view of right side.

The metascutellum, a median, elevated, and often smooth area of the metanotum, is absent in P. kleio. In this species the entire metanotum is uniformly foveate (Figure 16), contrasting with the rest of Platygastridae in which a metascutellum is clearly differentiated, when visible. It should be noted that in some derived platygastrine genera the posterior margin of the mesoscutellum overlaps the metanotum and articulates directly with the lateral propodeal carinae, thus obscuring the metascutellum. The phylogenetic analyses of Chen et al. (2021) retrieved Platygastridae in a clade with Janzenellidae and Neuroscelionidae, both of which have a metascutellum, suggesting that its absence in P. kleio is not a plesiomorphy. Similar to P. kleio, the uniformly foveate metanotum without a metascutellum occurs in Proterosceliopsidae and Huddlestonium exu Polaszek & Johnson (Geoscelionidae, Figure 18). Among other Cretaceous platygastroids, some of which require further study for family-level placement, the metascutellum is apparently absent or minimally differentiated from the metanotal trough (Figures 19, 20). It currently remains unclear at what level in the superfamily this character can be considered derived or ancestral, and the degree to which it is homoplastic.

Figures 18–20. 

18 Huddlestonium exu (OSUC 232305), mesosoma, posterior view 19 Platygastroidea sp., Burmese amber (CNU-HYM-MA-2017068), mesosoma, dorsolateral view 20 Sparasionidae sp., Burmese amber (CNU-HYM-MA-2016104), mesosoma, dorsolateral view.

The wing venation of Prototeleia, in which the stigmal vein is perpendicular to the marginal vein, is similar to that of the fossil platygastrid illustrated in figures 65, 66 in Talamas et al. (2019), and O. enigmaticum, which is the only extant platygastrid with these veins (see figure 6 in Johnson et al. (2016)). A bulla in the fore wing is found in both platygastrid specimens known from the Cretaceous and is not found in extant members of the family.

Figures 21–24. 

21 Prototeleia kleio, paratype male (OSUC 226542), metasoma, ventrolateral view.

The transverse line of foveae along anterior T2 (Figures 1–3, 21) is found in only a few platygastrids, including Orwellium, Metaclisis and Prototeleia, but is ubiquitous in Sparasionidae and nearly so in Scelionidae. Prototeleia kleio is unique among platygastrids by having lines of foveae on anterior S3–S4 (Figures 6, 17, 21), which are deeply impressed and costate, especially in the male specimen. In all other platygastrids, except Sacespalus, S3–S6 (or the terminal segment) are simple. In Sacespalus, pits are present in the anterolateral corners of S3–S5 (Figures 22, 23). We consider anterior, transverse lines of foveae on metasomal segments 1–5 to be the ancestral condition in Platygastroidea based on its prevalence in the Cretaceous fossils that we have examined (Burmese and Lebanese amber). We thus interpret Prototeleia kleio to be a transitionary form, one that clearly belongs in Platygastridae while exhibiting a plesiomorphy not present in the extant fauna.

The relative length of the second metasomal segment is a useful character for Platygastridae because essentially all members of the family have this as the longest segment. The rare exceptions are species with an extremely elongated metasoma, as is known to occur in some species of Synopeas Forster and Platygaster Latreille (Figures 25, 26). Metasomal segments of roughly equal length can be found in Scelionidae, but this is not typical, whereas in Sparasionidae, Nixoniidae, Proterosceliopsidae, and the unplaced Proteroscelio Brues, the segments are generally equal in length. We thus consider T2/S2 as the longest segment to be a derived character for Platygastridae. The metasoma of Prototeleia appears to be an intermediate form: T2/S2 is the longest, but only slightly so in comparison to the extant fauna.

Figures 25, 26. 

25 Synopeas idarniforne (Dodd) (SAMA No. 32-032767), habitus, lateral view 26 Platygaster prolata MacGown (USNMENT01059214), habitus, dorsal view.