Mecistostethus Marseul, 1870

Caterino, Michael S., Tishechkin, Alexey K. & Degallier, Nicolas, 2012, A revision of the genus Mecistostethus Marseul (Histeridae, Histerinae, Exosternini), ZooKeys 213, pp. 63-78 : 65-66

Genus Mecistostethus Marseul, 1870

Mecistostethus Marseul 1870: 123.Type species Mecistostethus pilifer Marseul 1870: 123, by monotypy.

Tarsilister Bruch 1932: 278. Type species Tarsilister loretoensis Bruch 1932: 279, by original designation; NEW SYNONYMY.

Diagnosis.

The genus Mecistostethus is easily recognized on the basis of numerous autapomorphies, most significantly the elevation of the mesoventrite as a strongly protruding keel (Fig. 2A) (as opposed to the typically coplanar meso+metaventrite and prosternum), as well as the posteriorly arcuate margin of the metaventrite, projecting deeply into the 1st abdominal ventrite (Fig. 2A). In addition the setose body (Fig 1 A–B), broadened tibiae (Fig. 2a), convex frons (Fig. 2B), and elytra which are depressed in the posterior third (Fig. 1B), completely lacking dorsal striae 3-5 and sutural stria combine to make this one of the most easily recognizeable New World Histerinae genera.

Description.

Size range: Length 1.8-2.7mm; width 1.4-2.2mm; Body shape: Body elongate oval, moderately flattened, rufescent to rufo-piceous, variably microsculptured. Head: Frons strongly convex, with epistoma slightly declivous, disk setose, with or without granulate microsculpture; frontal stria outwardly arcuate and subcarinate when present, absent from some species; subraorbital stria present and continuous with sides of frontal stria; labrum about twice as wide as long, apical margin weakly emarginate; mandibles rather short, lacking subapical teeth; antennal scape elongate, slightly swollen subapically; antennal club oval, tomentose, lacking sutures or distinct annuli, with two small dorsal sensoria near apex of upper surface (Fig. 2C); submentum with sutures weakly impressed, bearing a few setae; mentum flat, nearly twice as broad as long, slightly tapered toward apex, apical margin shallowly emarginate; palpi elongate, with apical palpomeres acuminate. Pronotum: Pronotum with sides rounded, narrowed to apex, anterior emargination simple, prescutellar impression absent; pronotal discal gland openings small, annulate, situated about one-third from anterior margin (just beyond ends of recurved anterior submarginal stria, when present), approximately head-width apart; disk generally with punctures near sides and bearing setae variously arranged; marginal stria complete, free anteriorly, bearing 8-11 setae; lateral submarginal stria forming a shallow depression close to marginal stria; anterior portion of marginal stria continuous with lateral submarginal stria; anterior submarginal stria sometimes present, with ends free and recurved posterolaterally. Elytra: Epipleuron lacking striae; dorsal elytral striae subcarinate and bearing setae; outer subhumeral stria complete, cariniform, forming a lateral elytral margin; inner subhumeral, 1st and 2nd dorsal striae more or less complete and convergent to posterolateral corner; other elytral striae absent. Prosternum: Prosternal lobe short, extending to hypomeron, with medial fragments of marginal stria in some; prosternal keel posteriorly emarginate, but covered by strongly produced mesoventral process; striae of prosternal keel present or absent. Mesoventrite: Mesoventrite strongly elevated (Fig. 2A), subacute anteriorly, projecting over base of prosternum; marginal mesoventral stria complete; mesometaventral stria present or absent. Metaventrite: Posterior margin of metaventrite strongly produced posterad. Abdomen: Abdominal ventrites smooth to faintly punctate; abdominal ventrites 2-5 with stria along posterior margin; propygidium short, flat, with two anteromedial gland openings and lateral marginal striae; pygidium rounded apically, setose, with fine marginal stria (Fig. 2D). Legs: Protrochanter with single seta; protibial margin even, bearing fine marginal spines; protibial spurs present, weak; protarsal setae expanded; male protarsal claws simple; meso- and metatibiae expanded, with even, weakly spinose margins; meso- and metatarsi with numerous ventral setae. Male (Fig. 5): Paired accessory sclerites present, weak and small; 8th tergite with broad basal and narrower apical emarginations, line of basal membrane attachment complete, just distad basal emargination, ventral apodemes widely separated along midline; 8th sternite with halves separated, apical guides moderately to strongly developed, narrowed apically; 9th tergite with strong ventrolateral apodemes, about one-third from apex; spiculum gastrale (S9) rather narrow, only slightly expanded at base, more weakly sclerotized along midline, with deep, narrow apical emargination, apical flanges not strongly developed; 10th tergite entire, not divided along midline; basal piece slightly elongate, from one-fourth to one-third tegmen length; tegmen narrow, variably expanded to apex, with basolateral carinae converging to delimit a ventral concavity, in some with a thin median keel within this concavity; median lobe from one-fourth to one-half tegmen length. Female: 8th tergite united, emarginate apically, with secondary apicolateral emarginations; 8th sternite divided into one central and two lateral plates, the basal baculi separate, articulated with the lateral plates; 9th sternite present as a median plate, with a sclerotized basal connection to sternite 8; 10th tergite present, undivided; valviferae enlarged at base, articulated with coxites; coxites about one-half length of valvifers, about twice as long as maximum (basal) width, with strong inner apical tooth and much weaker outer one; gonostylus present, setose; bursa copulatrix lumenous, without sclerites; spermatheca and associated glands not examined.

Distribution.

The species are exclusively South American, but with scattered records from a surprising variety of biotopes, including Atlantic forests of Santa Catarina, Brazil, cerrado of Mato Grosso do Sul, lowland Amazonian forest of Ecuador and low to mid-elevations on the Guianan shield of French Guiana.

Remarks.

All recent collections have been through the use of flight interception traps, and consist solely of male specimens. Only two female specimens of the genus are known, both of Mecistostethus loretoensis (Bruch).

Key to species