Exebotrigona Engel & Michener, 2013

Engel, Michael S. & Michener, Charles D., 2013, A minute stingless bee in Eocene Fushan amber from northeastern China (Hymenoptera: Apidae), Journal of Melittology 2013 (14), pp. 1-10 : 2-4

Exebotrigona Engel & Michener , new genus

ZooBank: urn:lsid:zoobank.org:act:FEF5D1E6-D3F7-44D0-B1DD-ADED18B20814

TYPE SPECIES: Exebotrigona velteni Engel & Michener , new species .

DIAGNOSIS: Workers minute, forewing length ca. 2 mm; integument shining, faintly imbricate to smooth, with minute widely-scattered punctures on head and mesosoma, apparently without maculations. Head as broad as mesosoma; vertex weakly procurved posterior to ocelli, not produced or ridged; ocelloccipital distance slightly more than one median ocellar diameter; interocellar distance about three times median ocellar diameter, slightly greater than ocellocular distance; scape shorter than alveolocellar distance, not reaching median ocellus (as in Trigonisca Moure s.str., not Dolichotrigona Moure ); ocelli near top of vertex (as in Trigonisca s.str.); middle flagellomeres about as long as wide, second and first about as long as wide; distinctly not longer than wide (as in Trigonisca , not Dolichotrigona ). Mesoscutum with notauli faintly evident, not impressed; median line distinctly impressed but not strong; mesoscutellum short, rounded and thick in lateral aspect, slightly overhanging metanotum, shining transverse depression on mesoscuto-mesoscutellar sulcus simple (not extending medioposteriorly into mesoscutellum as V-shaped fovea); propodeum apparently slightly declivitous, basal area apparently short, smooth and shining (not reticulate as in most Trigonisca , except smooth in Leurotrigona Moure ).

Setae on body mostly short and inconspicuous, mesoscutum and disc of mesoscutellum almost bare but posterior margin of mesoscutellum with sparse straight bristles radiating posteriorly, longest ones about two-thirds as long as median length of mesoscutellum (as in Lisotrigona Moure ).

Forewing extending beyond apex of metasoma, without submarginal crossveins (second abscissa Rs, 1rs-m, 2rs-m), no indication of submarginal cells; pterostigma large, margin in marginal cell slightly convex; marginal cell with base broad, basal angle as measured between pterostigmal vein and r-rs nearly orthogonal; apex of marginal cell acute, open only by one vein width and closed by pigmented membrane or nebulous vein (more extensively open in other genera, except some Celetrigona Moure ); marginal cell width at pterostigmal apex distinctly greater than distance across submarginal area (as measured from apical abscissa of Rs to M); submarginal angle (as measured between first free abscissa Rs and Rs+M) orthogonal; M terminating without defined bend at position of nebulous 1m-cu, continuing as nebulous vein beyond termination; distal abscissa Cu nebulous [Cu1 and Cu2 sensu Engel (2001) nebulous], not defined by tubular and pigmented vein. Hind wing partly visible through forewing, apparently without closed cells.

Metatibia about three times as long as greatest width (an estimate; base of tibia hard to see); outer surface gently concave, glabrous; posterior margin gently convex, not tuberculate (more or less tuberculate in most Trigonisca s.l.); distal margin transverse; posterior distal angle distinct, rather sharp, nearly orthogonal; setae along posterior margin dense, elongate, simple (none branched or plumose), and widely spaced ( Fig. 4 ); rastellum apparently represented by slender setae (not a coarse comb as in related genera); inner surface of tibia with broad median zone convex, coarsely punctuate (although partly hidden, almost certainly without finely punctate keirotrichiate area and without smooth bare area); median zone with setae directed posterodistally, probably tapering to pointed apices (but not clearly visible) (not very minute and dense like keirotrichiae of related genera), this zone separated from shining posterior marginal zone by weak slope; marginal zone bare, depressed, shining, medially about one fifth as wide as maximum tibial width but gradually narrower both basally and distally; anterior margin of tibia with distinct narrow, parallel sided, shining, hairless, depressed zone about one sixteenth as wide as tibia; metabasitarsus length about 2x width, about 0.6x as wide as metatibia, inner surface without basal sericeous area, with setae arranged in loosely-defined transverse rows (similar to those of Trigonisca s.l. and Apis Linnaeus ).

ETYMOLOGY: The new genus-group name is a combination of exebos (Greek, meaning “past one’s youth”) and Trigona . The gender is feminine.

Figures

Figures 2–4. Photomicrographs of holotype worker of Exebotrigona velteni, new genus and species, in Eocene amber from the Fushan Coalfield. 2. Left lateral habitus. 3. Right lateral habitus. 4. Detail of inner surface of metatibia and metatarsus (unclear areas are obscured by internal fractures from this particular view). Metrics of individual provided in description.