Megalocraerus mandibularis, Caterino, Michael S. & Tishechkin, Alexey K., 2016

Caterino, Michael S. & Tishechkin, Alexey K., 2016, A revision of Megalocraerus Lewis, 1902 (Coleoptera, Histeridae: Exosternini), ZooKeys 557, pp. 59-78 : 66-70

Taxon classification Animalia Coleoptera Histeridae

Megalocraerus mandibularis sp. n. Figs 5 A–B, 6 A–B, 8

Type material.

Holotype male: "FRENCH GUIANA, KAW, xii 2014, leg: J.L.GUIGLARIS" (FMNH).

Diagnosis.

This species is very distinctive, at least in the male, exhibiting unique dorsobasal mandibular processes (Fig. 6). Because only the male is known, it is unclear if these are secondary sexual characters or not, though it seems likely. Otherwise the species is very similar to Megalocraerus chico known from southern Central America. The two differ in tarsal setae, with Megalocraerus mandibularis having simple ventral setae, while Megalocraerus chico has sublaminate setae. In addition, Megalocraerus mandibularis has rather more numerously and strongly dentrate tibiae, than any other species, with the mesotibia in particular exhibiting 6 distinct spinose teeth. Other species generally show fewer and less deeply divided tibial teeth on all legs. Finally, the basal elytral stria, uniting the bases of the marginal epipleural through sutural dorsal striae, is more strongly and completely impressed here than in other species, although the extent of variation in this character in other species is difficult to assess with limited material. The male genitalia are highly distinct, showing strong dorsoventral curvature.

Description.

Size: Length 2.8 mm; width 2.0 mm; Body: broad, subparallel-sided, elongate, weakly depressed; darkly castaneous. Head: Frons finely and doubly punctate, with medium punctures separated by slightly more than their diameters against fine ground punctuation, decreasing in size but slightly increasing in density anteromediad, sparser toward the eyes; frontal stria present along inner margins of eyes, bent inward above antennal insertions, broadly interrupted across epistoma; faint fragments of supraorbital stria present; epistoma depressed, narrowing anterad; labrum minutely punctate; mandibles each with inner marginal tooth and (in male) with bluntly triangular dorsobasal process. Pronotum: Pronotal sides weakly convergent to anterior corners, marginal stria present along sides and front, very briefly interrupted behind eyes; pronotal disk rather finely and sparsely punctate, puncture density diminishing basomedially, with finer ground puncta tion throughout; basal margin with a few coarser punctures near margin. Elytra: Two complete and an outer partial epipleural striae present; fine fragments of inner subhumeral stria present at middle; dorsal striae 1-4 largely complete, weak or fragmented apically; 5th stria interrupted near basal third, obsolete in basal sixth; sutural stria complete; inner epipleural, 1st-4th and sutural striae connected by distinct basal marginal stria; elytral disks with fine but conspicuous ground punctation throughout, coarser secondary punctures present in apical sixth, with few secondary punctures scattered in apical interstriae, particularly along the elytral suture. Prosternum: Prosternal lobe evenly, somewhat narrow rounded, complete to sides, marginal stria present only at middle for approximately buccal cavity width; prosternal keel with complete carinal striae diverging slightly front and rear, indistinct around basal projection. Mesoventrite: Anterior mesoventral margin evenly emarginate, with complete, marginal stria; mesometaventral stria absent; disk with very fine, sparse ground punctation, with few secondary punctures at sides. Metaventrite: Lateral metaventral stria present, extending toward outer corner of metacoxa, slightly abbreviated apically; postmesocoxal stria indistinct. Abdomen: Abdominal ventrites finely punctate at middle, slightly more coarsely at sides; propygidium strongly transverse, about four times as wide as long, coarsely punctate, with punctures separated by slightly less than their diameters, rather uniformly throughout; pygidium similarly coarsely punctate at base, punctures becoming finer and denser toward apex. Male: 8th tergite with broad basal emargination, ventrobasal processes rather weak, not meeting beneath, dorsally with narrow median emargination; halves of 8th sternite slightly separated along midline, apicomedial processes rather narrow, subacute; 9th tergite with blunt, incurved apices; spiculum gastrale (S9) broad basally and apically, abruptly narrowed near midpoint, apex shallowly emarginate; 10th tergite entire; basal piece about one-third tegmen length, narrowly cylindrical; tegmen flattened throughout, abruptly bent ventrad one-third from base, sides weakly, sinuately divergent from base two-thirds to apex, narrowing to apices; median lobe narrow, slightly more than one-half tegmen length.

Remarks.

We mention a 'French Guiana form’ known only from females (or specimens who lost their genitalia prior to study) in the key and below. There is some slight possibility that it represents the female of this species, based not only on the distribution, but also on the shared character of relatively strongly spinose tibiae. However, the size difference is substantial, with the male Megalocraerus mandibularis much smaller than the three known specimens of this other form. Additional material will be necessary to confidently address this question.

This species is named for its unique and prominent mandibular processes.