Scaptorus, Caterino, Michael S. & Tishechkin, Alexey K., 2014

Caterino, Michael S. & Tishechkin, Alexey K., 2014, New genera and species of Neotropical Exosternini (Coleoptera, Histeridae), ZooKeys 381, pp. 11-78 : 33-34

Scaptorus gen. n.

Type species.

Scaptorus pyramus sp. n.

Description.

This genus differs from other Exosternini in the following combination of characters: body elongate, sides subparallel, distinctly convex; frons widened to rounded anterior corners produced over antennal bases; epistoma bituberculate along anterior margin; labrum with apical margin truncate, weakly produced and carinate; left mandible with straight, edentate incisor edge, right mandible curved to apex, with small, acute basal tooth; submentum rather short, slightly depressed, weakly produced anteriorly into oral cavity; mentum broadly subquadrate, weakly emarginate apically, labial palpi 3-segmented, basal palpomere very short, penultimate and ultimate palpomeres rather thin and elongate; maxillary cardines very smooth, stipes faintly microsculptured, with few scattered setae, maxillary palpi 4-segmented, basal palpomere short, 2nd and 3rd palpomeres subequal, ultimate palpomere about twice as long as penultimate, simply fusiform; antennal scape elongate, very slightly widened toward apex, with few setae on anterior surface; funicle slightly shorter than scape, widened slightly to cupuliform 8th antennomere; antennal club elongate oval, about as long as funicle, tomentose, with median and subapical annuli crowded into apical half, both interrupted on dorsal surface, free ends enlarged into sensory patches, the apical-most more so; pronotal gland openings not evident; pronotal sides subparallel, abruptly bent to apical corners; transverse elevated carina present behind and parallel to anterior pronotal margin, curving posterad briefly at sides, abruptly bent to lateral margin behind anterior corner; prosternal keel overlapped at base by projecting mesoventrite, weakly convex, short, anteriorly displaced by prominent prosternal lobe, which is strongly produced, deflexed, with raised median ridge; mesoventrite subtrapezoidal, projecting anteriorly; mesometaventral stria absent; propygidium transverse, with small gland openings in anterolateral corners; pygidium about one third wider than long, apical margin simply rounded; protrochanter lacking setae, meso- and metatrochanters with pair of very short setae near apex of posterior edge; profemur rather narrow, anterior edge sinuate; protibia narrow at base, outer margin more or less rounded apically, weakly dentate, strongly spinose; protibial spurs present, short; protarsus somewhat laterally compressed, bearing spatulate ventral setae in both sexes; meso- and metafemora narrow; meso- and metatibiae slightly widened to apices, bearing few thin spines toward apex of outer margins; male genitalia with paired accessory sclerites present; T8 with ventral apodemes nearly meeting along midline; S8 with halves divergent apically, apical guides well developed, with subapical setae; T9 with broad, blunt ventrolateral apodemes; T10 completely divided; S9 head broad, with prominent lateral flanges, apical flange low, continuous, not interrupted medially; tegmen lacking medioventral tooth or process; median lobe long, basal processes strongly differentiated; female T8 forming a single plate; S8 tripartite, basal baculi narrowly articulated with lateral plates, thin and convergent proximally; S9 well developed, about twice as long as broad, articulated with strap-shaped extension from apex of S8; T10 entire; valvifers about as long as coxites, weakly paddle-shaped, weakly expanded in basal third; coxites nearly three times as long as wide, bidentate, with median apical tooth rather thin and elongate, outer tooth weakly developed, the two well separated; gonostyle flattened, shorter than median tooth, apically setose; bursa copulatrix membranous, barely expanded; spermatheca rather short, sausage-shaped, with basal stem short, with slightly thin, very elongate spermathecal gland attached near its base.

Remarks.

Scaptorus is characterized by numerous unique features. The transverse carina of the pronotum (Figs 13A, 14 A–B) is the most obvious, immediately separating this from other Neotropical Exosternini . But in addition the bituberculate epistomal margin, projecting mesoventral margin (overlapping the reduced prosternal keel), and longitudinally ridged prosternal lobe (Fig. 13B) are also very unusual. A somewhat comparable mesosternum can be found in Mecistostethus Marseul, but this is almost certainly convergence; the two genera share little else. It is instead resolved as closely related to Enkyosoma and Chapischema in our recent analysis of Exosternini relationships (Caterino and Tishechkin in review).

Etymology.

The name of this genus translates to 'shoulder ridge’ referring to its most diagnostic feature.