Tyrannoscelio Masner, Johnson, and Arias-Penna, 2007

Tyrannoscelio Masner, Johnson, and Arias-Penna View in CoL , new genus

figures 1–9 View Figs View Figs

DESCRIPTION: Length 3.1–4.2 mm; body cylindrical, almost cigar-shaped, with relatively short legs, antenna; head massive; mesosoma, metasoma normally proportioned; head, metasoma dark brown to black, mesosoma dark brown to rufous; macropterous.

Head ( figs. 1–6 View Figs View Figs ) remarkably large, distinctly longer than wide in dorsal view, length 1.5–1.6 times greatest width; upper frons strongly produced anteriorly into shelf ( figs. 3, 4 View Figs : fs), anterior margin produced into upcurved, truncate projections; hyperoccipital carina absent; occipital carina well developed, continuous medially, finely crenulate; lateral ocellus close to inner orbit of compound eye, OOL short, less than diameter of lateral ocellus ( figs. 1 View Figs , 5, 6 View Figs ); compound eye large, with scattered elongate setae ( fig. 5 View Figs ); frons largely flat or weakly concave, smooth, glabrous medially; area between compound eye, antennal insertion, and base of mandible deeply concave, corresponding to shift in position of anterior mandibular articulation, with arched rugulae parallel to base of mandible, moderately setose; interantennal process strongly produced anteriorly, torulus opening laterally from process; submedian carina absent; orbital carina present, extending along inner orbit, ventrally continuing toward posterior mandibular articulation; lower frons without fanlike striae; interocular space broad; inner orbits parallel; clypeus strongly raised beneath interantennal process; anteclypeus divided from postclypeus by strong arcuate carina, anteclypeus transverse, convex, dorsoventrally carinate, with four elongate setae arising from apical margin; postclypeus smooth, concave, apical margin strongly concave; malar sulcus absent; gena greatly expanded, convex, lower margin deeply notched at position of posterior mandibular articulation; labrum hidden beneath clypeus; mandible ( figs. 2 View Figs , 3, 4 View Figs : md) extremely long, directed anteriorly, anterior articulation deeply invaginated, posterior articulation shifted anteriorly to side of head, mandibular range of movement primarily dorsoventral, with weak transverse component; mandible with numerous strongly developed teeth along both inner and outer margins; maxillary palpus four-segmented, all segments cylindrical; labial palpus two-segmented; antenna 12merous in both sexes; radicle inserted apically into A1, nearly parallel to longitudinal axis of A1; A1 widest basally, gradually narrowed toward apex; A3 longer than A2; apical six antennomeres expanded into clava in female; gustatory sensilla on female antenna arranged in longitudinal pairs on apical antennomeres; claval formula A8-A12 1-2-2-2-1; male antenna ( fig. 9 View Figs ) without visible tyloids or differentiated sex segment, flagellomeres cylindrical, each constricted basally and apically, with erect setae.

Mesosoma ( figs. 1, 2 View Figs ) cylindrical, in dorsal view longer than wide, in lateral view deep, somewhat flattened dorsally; pronotum in dorsal view narrow laterally, anterolateral corners rounded; transverse pronotal carina absent; epomial carina absent; pronotal humeral carina present; anterior face of pronotum extremely narrow, hidden in dorsal view; lateral face of pronotum largely flat to weakly concave, facing anteriorly, without scrobe for reception of foreleg; netrion ( fig. 2 View Figs : n) very broad, as wide as tegula, fusiform, open ventrally; anterior margin of mesoscutum meeting pronotum anteriorly, not dorsally; mesoscutum semioval in outline; parapsidal lines absent; notauli present, nearly percurrent or abbreviated; skaphion present, narrow, posterior margin strongly carinate; transscutal articulation well developed, crenulate; scutellum ( figs. 7, 8 View Figs : sctl) wider than long, unarmed, convex, weak medial longitudinal furrow; axilla well developed; metanotum narrow, dorsellum ( figs. 7, 8 View Figs : d) clearly differentiated, produced into flat lamella, apical margin variable in armature; dorsal surface of propodeum with dense, fine pilosity; keels, plicae of propodeum not developed; posterior face of propodeum punctate, setose; mesopleuron large, prominent; mesopleural depression well developed; mesopleural carina indicated by line of crenulae or short, parallel longitudinal rugulae; sternaulus absent; mesopleural pit present, shallow; anterior margin of ventral portion of mesepisternum straight, not protruding between forecoxae; mesepisternum and mesepimeron separated by line of welldeveloped foveae; episternal foveae absent; dorsal corner of mesepimeron rounded, without posterior tooth; anteroventral portion of metapleuron rounded, not separated from lateral face by carina, setose; metapleural pit absent; posterior margin of metapleuron lamellate; metapleuron separated from propodeum dorsally by deep groove; propodeum without longitudinal carinae, setose throughout, posterolateral corners weakly projecting posteriorly; legs relatively slender; posterior surface of hindcoxa smooth; femora not incrassate; trochantellus present on all legs; outer surface of foretibia and midtibia with strong semierect spines; tibial spur formula 1- 1-1, tarsal formula 5-5-5; tarsomeres tapering in width apically, second tarsomere for foretarsus rather short; pretarsal claws simple; apex of forewing extending to T4 or beyond, moderately infuscate, marginal cilia short but distinct; R fairly straight, extending through basal 0.5 of length of forewing, extending to costal margin, with strong bristles arising throughout its length, costal portion (marginal vein) very short, nearly punctiform, wing membrane around this point infuscate, forming pseudostigma; R 1 absent or extremely short, therefore without postmarginal vein; rrs (stigmal vein) straight, arising from costal margin; no other tracheate veins in forewing; hindwing with R tracheate throughout its length, extending to hamuli and costal margin; no strong dark bristles on R; three hamuli present.

Metasoma ( figs. 1, 2 View Figs ) more or less cylindrical, terga slightly flattened, sterna deep, convex; T3 distinctly the longest tergite; female with 7 terga, 6 sterna visible externally, male with 8 terga, 7 sterna visible externally; submarginal ridge well developed, defined by narrow laterotergites to form deep submarginal rim; no spiracles visible; anterior margin of segment 1 deeply crenulate; suture between segments 1 and 2 basally crenulate; sutures between other segments simple; female T6 without median raised field of microsetae or secretion; S1 arched, not laterally compressed, not extending anteriorly between hindcoxae; anterior margin of S2 straight; narrow sublateral felt fields present on S2; ovipositor not dissected.

DIAGNOSIS: Distinguished from Sparasion by the 1-1-1 tibial spur formula, lack of bulla in R (submarginal vein), lack of a postmarginal vein; distinguished from Acanthoscelio by the well-developed, distinct forewing venation, the complete R in the hindwing extending to the hamuli, and the semicircular scutellum lacking lateral spines; distinguished from Encyrtoscelio and Breviscelio by the elongate metasoma with T3 being the longest tergite. Additionally, Tyrannoscelio can be separated from all these genera by the presence of a narrow skaphion at the anterior part of the mesoscutum.

TYPE SPECIES: Tyrannoscelio genieri Masner and Johnson , new species.

ETYMOLOGY: From tyranno -, master or despot, and scelio, the name for the nominal genus of the family, alluding to both its formidable head and that of the theropod Tyrannosaurus .

GEOGRAPHIC DISTRIBUTION: Neotropical, known from southeast Brazil (Espírito Santo) and Colombia (Caquetá).

COMMENTS: Tyrannoscelio does not fit naturally into the current, uncertain tribal classification of the Scelionidae . Three characters stand out as being of possible significance in assessing its relationships: the presence of a skaphion, the absence of a malar sulcus, and the absence of a sex segment in the male antenna.

The skaphion is an anterior subdivision of the mesoscutum. It is found in all genera of the Thoronini (sensu Masner, 1972), but is also scattered among other genera, including Parascelio Dodd (the only genus within the Parascelionini) and many Psilanteridini sensu Masner (1976) . Austin and Field (1997) strongly suggested that Psilanteridini is not monophyletic, and they provided evidence for a major monophyletic group within the Scelioninae, the Scelionini sensu lato, united on the basis of a suite of characters from the ovipositor. (We chose not to sacrifice one of the few female specimens of Tyrannoscelio in order to dissect the ovipositor, the character suite used to define Scelionini s.l.) When mapped onto their consensus cladogram ( Austin and Field, 1997: fig. 189), the skaphion appears in seven different lineages. Even when some of these are clustered together on the basis of this character, it appears that the skaphion has either appeared or disappeared at least three times in the course of scelionid evolution.

The malar sulcus, extending from the lower portion of the compound eye to the base of the mandibles, is a feature present in practically all Scelionidae . It is notably absent, however, in several of the genera usually considered to be basal within the family: Archaeoscelio Brues (an extinct genus from Baltic amber), Nixonia Masner , Sparasion Latreille , Sceliomorpha Ashmead , Plaumannion Masner and Johnson , Huddlestonium Polaszek and Johnson , as well as in practically all genera of Platygastridae (all except Metaclisis Förster and Orseta Masner and Huggert ). We consider it likely that the absence of a malar sulcus is plesiomorphic. Thus, its absence in Tyrannoscelio implies either that the genus must be excluded from a group comprising most scelionids, or that the sulcus has been secondarily lost, possibly in concert with the development of the other striking modifications of its head structure.

Finally, almost all scelionid and platygastrid males have one or more antennomeres modified into a so-called ‘‘sex-segment.’’ This segment is usually A 5 in scelionids and A 4 in platygastrids, and the ‘‘basal’’ genera Archaeoteleia Masner , Nixonia , Sparasion , and Sceliomorpha often have several antennomeres (up to five, from A4 to A8) bearing tyloids. Tyrannoscelio is one of very few species in the superfamily in which there appears to be no such modification. Notably, one of these is Archaeoscelio , although we must admit that this may be an artifact arising from the difficulty of observing minute features in amber material.

KEY TO SPECIES OF TYRANNOSCELIO

1. Mesoscutum and scutellum longitudinally rugose; notauli nearly percurrent; dorsellum semicircular; apical margin of frontal ledge with 10 projections; outer margin of mandible with three teeth ( Brazil)..................... T. genieri Masner and Johnson , n.sp. — Mesoscutum and scutellum punctate-rugulose; notauli very short; dorsellum tridentate; apical margin of frontal ledge with 14 projections; outer margin of mandible with five to six teeth ( Colombia)... T. crenatus Arias-Penna , n.sp.