Megalocraerus Lewis, 1902

Caterino, Michael S. & Tishechkin, Alexey K., 2016, A revision of Megalocraerus Lewis, 1902 (Coleoptera, Histeridae: Exosternini), ZooKeys 557, pp. 59-78 : 61-63

Taxon classification Animalia Coleoptera Histeridae

Megalocraerus Lewis, 1902

Megalocraerus Lewis, 1902: 231

Type species.

Megalocraerus rubricatus Lewis, by monotypy.

Diagnosis.

The genus is readily separated from other Histerinae in the Neotropics, where few other large cylindrical species have been described. In addition to this general body shape, the depressed epistoma and reduced, subtriangular labrum will distinguish any member of the genus easily.

Description.

Size range: Length 2.8-4.1 mm; width 2.0-2.6 mm; Body: elongate, parallel-sided, subcylindrical, slightly depressed; body castaneous to piceous, rarely bicolored with the elytral bases rufescent. Head: Frons broad, prominent, slightly bulging in front of eyes, becoming depressed and narrowing toward concave epistoma; frontal disc coarsely punctate; frontal stria deeply impressed along inner edges of eyes, angled anteromediad at front, interrupted across width of epistoma, free ends may be bent mediad or dorsad; supraorbital stria largely obsolete, fragments may be present at middle; labrum reduced, short and subtriangular, apex rounded to subangulate; mandibles rather short, more or less evenly curved to subacute apices, usually with prominent tooth on each incisor edge, lacking inner submarginal ridge; antennal scape moderately expanded to apex, with carina along outer posterior edge, funicle gradually expanded, antennomere 8 broadly cupuliform; antennal club rounded, not elongate, apex rounded to subtruncate, with apical and subapical annuli crowded into apical third, subapical annulus weakly expanded at middle of dorsal and ventral surfaces, basal annulus absent; gena narrowly depressed posterad cardo; gular sutures visible but not impressed; submentum short, with apical row of ~15 setae; mentum narrowing anterad, apex emarginate, with sparse setae; labial and maxillary palpi basically fusiform, narrowed apically. Pronotum: Pronotal sides subparallel, weakly rounded, narrowed anteriorly, apical emargination broad; vaguely but indistinctly depressed in prescutellar region; anterior gland openings very fine, present on sides of anterior emargination; marginal stria complete along sides, variably fragmented to obsolete along anterior margin; marginal pronotal stria very fine, continuous around lateral and anterior margins. Elytra: two (rarely three) complete epipleural striae present, innermost continued variably mediad along part of anterior elytral margin; inner and outer subhumeral striae at most weakly indicated, generally absent; striae 1-4 complete, 5th stria complete or basally abbreviated; sutural stria complete, connected to base of 5th or rarely 4th stria; elytral disc with coarser punctation toward apex, ground punctation usually very fine and sparse but may be coarser and more conspicuous; elytral striae tending to become prolonged mediad along the basal elytral margin, sometimes forming a distinct stria. Prosternum: Prosternal lobe broad, about two-thirds length of keel; with marginal stria variably obsolete at sides; prosternal keel weakly produced posteriorly, with two complete carinal striae free or joined at apices; lateral striae of keel widely divergent anterad along presternal suture. Mesoventrite: Anterior mesoventral margin broadly, not too deeply emarginate, with complete marginal stria, often with secondary fragments in anterolateral corners; mesometaventral stria absent. Metaventrite: Postmesocoxal stria short or indisinct; inner lateral metaventral stria variably abbreviated apically, not reaching metacoxa; disc with only fine ground punctation. Abdomen: Abdominal ventrite 1 usually with one more or less complete lateral stria, anterior margin lacking stria; propygidium short, 4 –5× broader than long, disc lacking obvious gland openings; pygidium with apical margin broadly rounded, lacking marginal stria. Legs: Protrochanter lacking setae; meso- and metatrochanters each with two very short setae (often abraded or lost); protibia acutely multidentate, with 5-6 lateral marginal spines and 2-3 fine apical marginal spines; two protibial spurs present, short; tarsal groove on anterior surface only well developed in apical fourth; protarsi not sexually dimorphic, with single pair of apical setae on most tarsomeres; mesotibial margin distinctly multidentate, with 3-6 marginal denticles; metatibial margin not toothed, but with several fine marginal spines, tarsal claws simple; apical tarsomere on all tarsi elongate, curved; ventral tarsal setae variable, simple to flattened and sublaminate. Male: accessory sclerites absent; 8th tergite subparallel-sided to narrowed apically, basal apodemes of 8th tergite with thin, acute ventral extensions curving distad, convergent medially, separated from body of tergite by deep lateral emarginations parallel to basal margin; ventrolateral lobes rounded to subacute, variably separated along ventral midline; 8th sternite divided along midline with inner edges parallel, more or less approximate, outer upper edges produced apically into narrow, convergent processes or broad lobes, apices with thin velar membrane between, lacking distinct setae; 9th tergite with apices narrow, roundly convergent, lacking setae, ventrolateral apodemes weak to distinctly dentate; spiculum gastrale (S9) generally wide-stemmed, relatively weakly sclerotized along midline, apices divergent but not strongly produced or hooked; 10th tergite entire or variously partially divided, usually evenly sclerotized but sometimes appearing more strongly sclerotized toward apex; basal piece about one-fourth tegmen length, with apicoventral apodemes produced, more or less convergent beneath base of tegmen; tegmen rather narrow, moderately to strongly dorsoventrally flattened, usually lacking medioventral process, apices divided, sometimes distinctly separated at tips; median lobe half or greater length of tegmen, with proximal arms bent near midpoint. Female: 8th tergite broad, relatively flat, deeply emarginate apically; 8th sternite undivided, with strongly sclerotized, straight basal apodemes; valviferae weakly expanded proximally; coxite simple, only weakly differentiated into upper and lower surfaces, lacking apical teeth, apex narrowed, subtruncate, with prominent, setose gonostyle; bursa copulatrix membraneous; spermatheca forming a short, bulbous sac, inserted beneath apex of bursa, bearing single thin spermathecal gland near its base.

Distribution.

This genus is known from Central and South America, from Costa Rica in the north to Rio de Janeiro state (Brazil) in the south. However, there are many gaps, with records only from Costa Rica, French Guiana, Ecuador, Peru, and Brazil, though it almost certainly occurs in the intervening areas.

Natural history.

No specimen labels reveal any details of the natural history of the species of Megalocraerus , with all or nearly all specimens collected using flight interception ( ‘window’) traps. Given the subcylindrical, elongate morphology, an under-bark habit may be suggested, but there is no direct evidence for any such association.