Pyxister, 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 : 25-27

Pyxister gen. n.

Type species.

Pyxister devorator sp. n.

Description.

Size range: Length 2.4-2.8 mm; width 1.6-1.9 mm; Body: body elongate, subcylindrical, sides parallel, rufobrunneus, variably punctate, glabrous. Head: frons weakly to strongly depressed at middle, subangulate at sides in front of eyes, frontal stria complete to strongly reduced, supraorbital stria present, detached; epistoma and labrum varied; mandibles strongly toothed; mouthparts rather strongly recessed in oral cavity; submentum flat, produced in front; mentum subquadrate, nearly as long as broad, bearing sparse long setae; ultimate labial palpomeres elongate, slightly compressed; cardo glabrous, stipes with few long setae on lateral margin; ultimate maxillary palpomere slightly compressed; antennal scape elongate, curved, widest near midpoint; funicle shorter than scape, widening from antennomere 4-8, 8th antennomere cupuliform, more or less disclike; antennal club short, tomentose, with single, slightly elongate, axial sensory patch on ventral surface and longer patch on dorsal surface. Pronotum: pronotal sides more or less straight, slightly convergent to apex; prescutellar impression faintly impressed to obsolete; pronotal disk with two median gland openings on each side, one very close to margin behind eye, one posterad just behind pronotal midpoint; marginal pronotal stria present on lateral and anterior margins, may be complete or interrupted at sides; submarginal pronotal stria may be present at sides. Elytra: elytra slightly depressed along suture; epipleuron with single, complete marginal stria, outer subhumeral stria interrupted at middle, inner subhumeral stria absent, striae 1-5 present, 1 and 5 may be abbreviated, sutural stria complete. Prosternum: prosternal keel emarginate at base, carinal striae present, more or less complete, convergent anterad, joined in anterior arch; prosternal lobe short, slightly deflexed, marginal stria present. Mesoventrite: mesoventrite wide, short, with marginal stria fine, close to edge, may be interrupted; mesometaventral stria strongly angulate forward nearly to margin. Metaventrite: postmesocoxal stria poorly developed, short; lateral metaventral stria extending from inner corner of mesocoxa toward middle of metacoxa, abbreviated or not. Abdomen: 1st abdominal ventrite with single, oblique lateral stria; propygidium slightly convex, about two-thirds length of pygidium, gland openings may be visible near anterolateral corners; pygidium moderately to strongly convex, apical margin rounded. Legs: trochanters with single long seta; femora moderately elongate; protibia with outer margin rounded, moderately strongly dentate, with 5-6 spinose teeth; two protibial spurs present, meso- and metatibiae narrow to moderately widened to apex, mesotibia with entire margin spinose, metatibia spinose toward apex; protarsi (of male only?) with spatulate ventral setae. Male genitalia: accessory sclerites absent; T8 with narrow subacute apical emargination, ventral apodemes well developed but separated beneath, basal membrane attachment line intersecting slightly sinuate basal emargination; S8 with halves approximate in basal half, apical guides increasingly wide toward apex, rather abruptly narrowed to narrowly rounded apices, with only very fine inconspicuous setae; T9 with basal apodemes short, apex narrowly subacute, ventrolateral apodeme weakly hooked; T10 undivided; S9 desclerotized along midline, with deep apical emargination, apical flange interrupted, apical corners produced; tegmen with sides subparallel in basal two-thirds, slightly widened to subquadrate, subtruncate apex, lacking medioventral process; median lobe simple, about one-third tegmen length; basal piece short, with strong apicoventral articulating process. Female genitalia: T8 entire, with narrow apical emargination; S8 undivided, only emarginate apicolaterally, basal baculi strongly, arcuately convergent at base; S9 present, short, connected to S8 by sclerotized strap; T10 entire; valvifers gradually expanded to base, paddles about half total length; coxites large, about two-thirds valvifer length, strongly bidentate; gonostyle slightly shorter than median tooth, setose; bursa copulatrix entirely membraneous, weakly expanded; spermatheca globose; spermathecal gland not evident in preparation.

Remarks.

The cylindrical body shape of Pyxister (Fig. 9 A–B) will help separate it from most other Neotropical Exosternini . However, there are scattered species in many larger genera, as well as a few genera ( Yarmister Wenzel and Megalocraerus Lewis, in addition to the new genus Chapischema described below), in which a similar body form can be found. The genus can be separated from these by the combination of subangulate frons (Fig. 9 C–D), dentate mandibles, antennal club lacking annuli but with small longitudinal sensory patch (Fig. 8E), second median pronotal gland openings strongly displaced posterad, sutural elytral interval impressed, prosternal keel distinctly emarginate (Fig. 9 G–H), and the mesometaventral stria nearly reaching anterior mesoventral margin, disrupting or interrupting marginal stria. It is unfortunate that the male is known for only one of the species, but unusual genitalic characters (Fig. 10) include the lack of accessory sclerites, apically broadened tegmen, lack of medioventral tegmenal process, and strong apicomedial process of the basal piece. In the female (only Pyxister labralis ), the undivided 8th sternite is unusual among Neotropical Exosternini . In our recent analysis of Exosternini relationships (Caterino and Tishechkin in review), Pyxister emerges from within the poorly-defined 'scutellar impression group’, close to species with which it shares few obvious characters. Its relationships remain to be fully resolved.

Etymology.

Pyxis = canister or casket, referring loosely to the cylindrical body form, masculine.

Key to species of Pyxister