Enkyosoma, 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 : 21-22

Enkyosoma gen. n.

Type species.

Enkyosoma rockwelli sp. n.

Description.

This genus differs from other Exosternini in the following combination of characters: body widest behind middle, subdepressed, somewhat flattened dorsally, metaventrite rather abruptly convex ventrally, glabrous, lacking secondary punctation, and almost entirely lacking typical striae; frons more or less coplanar with vertex; labrum broad, apically emarginate, lateral margins with conspicuous setal fringe; mandibles with short incisor edges; antennal scape elongate, slender, curving posteroventrad beneath eye; funicle about as long as scape, weakly widened distally, the 8th antennomere cupuliform, no shorter than preceding antennomeres; antennal club elongate oval, completely tomentose, with two nearly complete setose annuli more distinctly interrupted on dorsal surface, only slightly curved basad at middle; eye substantially reduced; pronotum lacking prescutellar impression, though fine prescutellar fovea may be present, with three median gland openings on each side, one in anterior angles, one behind eye about one funicle width behind anterior margin, one displaced posterad on disk; three distinct gland openings also present along lateral pronotal margin; elytra with few striae extremely fine, inconspicuous; prosternal keel depressed, rather broad, produced at base; prosternal lobe deflexed; mesoventrite anteriorly emarginate; metaventrite strongly convex posteriorly, posterior margin arcuate; propygidium transverse, with single gland openings in anterolateral corners; pygidium large, apically rounded, without gland openings or marginal striae; trochanter with 2-3 short apical setae; femora moderately broad, slightly flattened; protibia subtriangular, with outer edge weakly outwardly rounded, not distinctly toothed, with numerous distinct marginal spines; two small protibial spurs present; all tarsi rather long and curving, with numerous ventral spines, those of protarsus (of male only?) strongly spatulate; mesotibia moderately expanded toward apex, metatibia less so, both with nearly complete series of marginal spines; male genitalia (Fig. 6) with paired accessory sclerites present; apices of S8 bearing only very fine, inconspicuous setae; T10 completely divided; S9 with head broad, subquadrate, with complete apical flange; tegmen narrow and elongate, sides parallel in basal half, narrowed to thin, ventrally curved apex, median foramen basad apical narrowing, ventral surface with basal tooth formed by thin median keel; Female not known.

Remarks.

This genus is easily recognized by its relatively large, rounded, subdepressed body form (Figs 5A-C), and its complete lack of elytral striae. Its spinose, slightly dilated tibiae and strongly convex metaventrite are also unique features.

In our recent analysis of Exosternini relationships (Caterino and Tishechkin in review) Enkyosoma is resolved as closely related to Scaptorus and Chapischema , the three of them forming the sister group to Operclipygus . However, only three characters change on the branch supporting this group (loss of 5th dorsal elytral stria, reduction to a single seta on the protrochanter, and the differentiation of the proximal apodemes of the male median lobe), and none are particularly substantial or unique. In gross morphology there are no obvious similarities among the three.

Etymology.

From the Greek, literally 'pregnant body’, referring to the strongly convex metaventrite.