Thyreomelikertes Engel, 2024

Thyreomelikertes Engel , new genus

TYPE SPECIES: Thyreomelikertes electrosinicus , new species.

DIAGNOSIS: This is a distinctive genus (figs. 20–31), noteworthy for the flattened, trapezoidal mesoscutellum that projects posteriorly well over the metanotum and wholly declivitous propodeum (figs. 23A, 27). In addition, the mesosoma is densely setose, giving the bees a shaggy appearance (figs. 20, 21, 23A, 26, 27). The clypeus lacks the protrusions and other modifications that characterize several genera of Melikertini . Among other genera, the new genus is similar to that of Mochlomelikertes Engel, Breitkreuz, and Ohl in Baltic amber as both have elongate and projecting mesoscutella, although that of the latter is vastly more extreme and covers portions of the metasoma (refer to Engel et al., 2014). Mochlomelikertes is noticeably larger at 8 mm in total length (forewing length 6.75 mm), while species of Thyreomelikertes are less than 6 mm in length.

A full diagnosis for the genus is as follows: Small bees, less than 6 mm in length; integument seemingly dark brown to black, without maculation (figs. 20–31). Mandible with outer mandibular grooves largely reduced, outer ridge prominent, faint indication of auxiliary ridge, clear acetabular groove and pollicar basin, latter divided into auxiliary basin, rutellar basin evidence, condylar ridge forming dorsal ramus apically (refer to Discussion), basins vanishing preapically and proximally, apical margin oblique, with shallow, broad incision demarcating short first preapical tooth, above which a broad concave margin between first preapical tooth and second preapical tooth at upper edge of mandible (upper distal angle), condylar groove in apical third with line of 3–4 long, ventrally directed, suberect (obliquely angled toward apex of mandible), thickened, flat setae (fig. 22); malar space linear (fig. 22); labrum flat, slightly broader than long, lateral margins parallel (not converging apically), without lateral fringe setae, apical margin with broad, shallow concavity medially, weakly and broadly rounded lateral to concavity (resulting in a weakly and broadly bilobed appearance to apical margin), surface with sparsely scattered long, fine, erect, simple setae, apical margin with numerous long, simple, fuscous setae, such setae thicker than those of disc; clypeus weakly convex, unmodified (i.e., without clypeal specializations or protrusions); epistomal sulcus laterally forming obtuse angle; upper torular tangent slightly below head midlength; scape elongate, longer than torulocellar distance; flagellomere I longer than wide, longer than flagellomere II; ocelli high on vertex, situated above upper tangent of compound eyes; vertex rounded in facial view, unmodified (no depressions or ridges); preoccipital area rounded; gena narrower than compound eye in profile.

\Mesotibia elongate; mesotibial spur present, simple, elongate; mesotibia and mesobasitarsus densely setose (fig. 24), setae intermixed with bristles, some setae minutely branched and sometimes capitate (fig. 24) (in T. electrosinicus ); metatibia slender, elongate (fig. 25A), posterior margin gently convex and slightly widening medially; surface of corbicula not depressed; posterior margin with fringe of long plumose setae (branches minute and along length of setal rachis) (fig. 25B), anterior margin with simple or minutely branched setae and bristles, corbicular surface with scattered, erect bristles and long setae; inner surface with keirotrichiate zone field covering most of surface except posterior, narrow, slightly depressed (i.e., a weak clivulus present) subglabrate zone and a broad, squarish apical subglabrate zone (sensu Rasmussen et al., 2017), latter with some scattered short, suberect bristles, apical subglabrate zone slightly longer than apical width of metatibia; rastellum composed of stiff bristles along entire inner apical width of metatibia; single metatibial spur present, spur minutely ciliate along inner margin; metabasitarsus with auricle present on proximal surface facing apex of metatibia; metabasitarsus rectangular (fig. 25A) to squarish, longer or slightly longer than wide, margins roughly parallel, apical margin comparatively straight to concave, inner surface with abundant, elongate, suberect, simple bristles arranged in loose comb rows; pretarsal claws with minute inner subapical ramus; arolium present (figs. 20, 21, 25A).

Metasoma broad, ovoid (figs. 20, 21), with scattered, short, erect to suberect setae, such setae more abundant laterally; metasomal sterna II–V with abundant, long, erect, fine, simple setae, those setae of sterna IV and V shorter and more suberect to decumbent; sting present (difficult to observe in type species, although with care it can be found, but easily seen in the second species where the sting is exserted), simple (i.e., without proximally directed barbs).

ETYMOLOGY: The new genus-group name is combination of the ancient Greek noun θυρεός (thyreos, meaning, “long shield”) and Melikertes , type genus of the tribe. The gender of the name is masculine.