Metapelma archetypon Gibson, 2009

Gibson, Gary, 2009, Description of three new genera and four new species of Neanastatinae (Hymenoptera, Eupelmidae) from Baltic amber, with discussion of their relationships to extant taxa, ZooKeys 20 (20), pp. 175-214 : 187-190

Metapelma archetypon Gibson , sp. n.

urn:lsid:zoobank.org:act:483192C9-E523-4884-84D0-99A5F82C6A75

Figs 27–32

Etymology. The Greek word archetypon , meaning “original” or “model”, in reference to the hypothesis that the head and hind leg structures represent uniquely retained groundplan states of the genus.

Type material. Holotype (Fig. 27): ♀, AMNH, labelled “ AMNH BaJWJ-407” / “ HOLOTYPE Metapelma archetypon Gibson ”. The unique female, along with partial remains of a spider, is in an almost rectangular, flat piece of Baltic amber about 13 × 11 × 3 mm. It is readily visible only from dorsal and ventral views and a white milky substance partly obscures dorsal mesosomal structure and gastral structure apically. Dorsal gastral structure is also partly hidden by the fore wings. Missing structures are left antenna beyond pedicel, right antenna beyond second funicular segment, right fore leg beyond about basal third of femur, right middle leg beyond tibia, left middle leg beyond part of basitarsal segment, and apical portion of ovipositor sheaths. The apical three segments of both hind tarsi are detached but are in the amber block.

Description. Length = 7.7 mm, excluding ovipositor. Body uniformly dark except at least metatarsus yellowish. Head not visible in frontal view, but with quite high and narrowly convex interantennal region (Fig. 28: iar) separating distinct scrobes from low convex parascrobal regions in ventral or dorsal view, and in dorsal view with combined scrobal depression shallowed dorsally and smoothly merged with frons below ocelli. Head in lateral view ovoid; length of gena ventrally posterior to eye about twothirds length of malar space; ventral margin of torulus about midway between lower occular line and oral margin. Head in dorsal view (Fig. 28) with vertex and temple rounded into occiput; transverse-rectangular, only about 1.7× as wide as long, with distinct temple about 0.25× head length; distance between eyes about 0.3× head width; posterior ocellus diameter equal to OOL and about 0.5× POL and 0.7× LOL; setal pattern not distinct but vertex, temples and occiput with white papilliform processes likely indicating setae surrounded by air pocket; occiput without occipital carina. Eye superficially bare (Fig. 28), but dorsal part of left eye with white, papilliform processes similar to head dorsally and indicating eye probably densely microsetose. Antenna with scape elongate, compressed-ovoid, and widened distally; funicle with fu 1 about 2.9× as long as wide, about 0.7× length of fu 2 and 0.75× length of pedicel. Pronotum in dorsal view about 0.5× length of mesoscutum, sides anteriorly convergent and posterior margin incurved (Fig. 27: no 1); apparently uniformly setose similar to mesoscutum. Tegula elongate-triangular with almost truncate posterior margin. Mesoscutum (Fig. 27) not shoulder-like posterior to pronotum, slightly longer than greatest width; largely

Figures 27–32. Metapelma archetypon sp. n. (♀ holotype): 27 dorsal habitus 28 dorsal head 29 scutellar-axillar complex 30 fore wings 3Ι lateral mesosoma, gaster and hind leg 32 apex of acropleuron to base of gaster, ventrolateral view.

obscured by milky substance but apparently with posteriorly ridge-like parapsidal lines (Fig. 27: psr) differentiating slightly concave, elongate rectangular median region from inclined lateral regions; uniformly and quite densely setose. Scutellar-axillar complex (Fig. 29) with deep, longitudinally crenulate scutoscutellar sutures differentiating conspicuously convex scutellum and axillae, and entirely setose except with narrow median bare band over about apical two-thirds of scutellum; axillae with dorsal surfaces (Fig. 29: das) transverse-triangular and apparently with contiguous inner angles; scutellum with strong longitudinal carina (Fig. 29: scc) extending along side from near middle of inclined posterior surface of axilla. Metanotum concealed by milky white substance except for left panel lateral to dorsellum; panel wide laterally and narrowed medially toward apparently somewhat concave and posteriorly protuberant dorsellum (Fig. 29: dor) beneath and well separated from scutellar apex. Propodeum concealed by milky white substance except for left side, apparently without differentiated plical and callar regions but depressed anteromedially under dorsellum and with posterior margin (foramen) shallowly incurved (Fig. 29: pfr); spiracle near midlength laterally. Prepectus triangular, about as long as high with dorsal and ventral margins forming obtuse posterior angle (cf. Fig. 19). Mesopleuron with acropleuron (Fig. 32: ac) extending slightly posterior of level of anterior margin of mesocoxa (Fig. 32: cx 2), with linear acropleural sulcus extending anteroventrally from mesocoxa for at least about one-third length before obliterate; mesepimeron a convex, arcuate-subtriangular region above base of mesocoxa, the region subdivided by deep sulcus into quadrangular lower mesepimeron (Fig. 32: lep) comprising about ventral third and triangular upper mesepimeron (Fig. 32: uep) comprising about dorsal two-thirds. Metapleuron entirely setose, more or less triangular in lateral view but ventral margin narrowly truncate above base of mesocoxa between mesepimeron and metacoxa. Mesosternum largely concealed, but with sulcate discrimen. Presence or absence of protibial apical spicule not visible. Middle legs long; mesocoxa with large basolateral cavity (cavity faced anteriorly because only visible mesocoxa twisted and slightly rotated out of fossa, Fig. 32); presence or absence of mesotibial pegs not visible, but tibial spur about 3× as long as apical width. Hind leg (Fig. 31) with metatibia 9× as long as maximum width, slightly narrower than femur with dorsal and ventral margins subparallel over most of length, and compressed-oval in cross section, dorsal margin apparently angulate but not carinate or thin; metatarsus with segments compressed-cylindrical, subequal in width and without carinate dorsal margin; basitarsus about 8x as long as wide. Fore wing (Fig. 30) hyaline; costal cell extensively setose along leading margin, but bare along submarginal vein; basal cell and disc completely setose except for very narrow linea calva not quite extending to basal fold; cubital and vannal areas bare except for some setae along posterior margin of vannal area distally; cc: mv: pmv: stv = 5.5: 1.8: 4.0: 0.9; stigmal vein with distinct uncus. Gaster very broadly sessile, elongate-fusiform, with at least 7 setose gastral tergites (structure of distal tergites not clearly visible, but apparently with deep suture lateral to cercus subdividing apical tergite and with Gt 6 extending dorsally over most of subdivided region); without projecting anal filament; hypopygium extending about 0.85× length of gaster. Ovipositor sheaths projecting, slender and obviously elongate, but apices missing.

Biology. Unknown, but likely the species was a parasitoid of wood-boring beetles based on structure of its ovipositor sheaths (Fig. 27) and hypothesized relationships with other species of Metapelma .

Remarks. Because of its preservation several important features cannot be seen clearly in the unique female of M. archetypon though it does appear to have posteriorly ridged parapsidal lines (Fig. 27: psr) and relative dimensions of its metanotum and propodeum are at least similar to extant Metapelma (cf. Figs 2, 29). Most features that are clearly visible, such as the scutellar-axillar complex, acropleural sulcus, pronotum, tegula, and fore wings are very similar to extant Metapelma . Phylogenetically most significant is that M. archetypon has a deeply divided upper and lower mesepimeron separating the acropleuron and metapleuron (Fig. 32), which is unique to Metapelma (Figs 19, 20) ( Gibson 1989, character 3, state 2). It differs conspicuously from extant Metapelma by having normal hind legs (Fig. 31). Extant species are uniquely characterized by laminately compressed metatibiae and metatarsi, and the metatarsal segments being obviously narrowed distally. The head of M. archetypon also appears to be more ovoid in lateral view than for extant species, having a comparatively long vertex and temples as well as a much more highly convex interantennal region (Fig. 28: iar) and longer, deeper scrobes. This latter structure is similar to what Gibson (1989, character 3, state 1) hypothesized as the ground plan structure for Neanastatinae and indicates that the somewhat lenticular head and short, furrow-like scrobes of extant Metapelma ( Gibson 1989, fig. 14) evolved convergently to the similar head structure of Neanastatus ( Gibson 1989, fig. 13) rather than being a synapomorphy for the two genera. Based on the above hypotheses of character-state transformation and relationships I hypothesize that M. archetypon is the sister species of all extant Metapelma and prefer to expand the generic limits of Metapelma to include it rather than to establish a new genus.