Osoriellus acutus, Irmler, 2014

Irmler, Ulrich, 2014, The Neotropical species of the genus Osoriellus FAGEL, 1959 (Coleoptera: Staphylinidae: Osoriinae), Beiträge Zur Entomologie = Contributions to Entomology 64 (2), pp. 231-354 : 295-296

Osoriellus acutus n. sp.

( Figs 106 A-C, 123F)

Type material: Holotype, male: Peru: Dept. Loreto, Campamento San Jacinto (75°51.77'W, 2°18.75'S), 175-215 m elevation, collected by flight intercept trap, 9.7.1993, leg. R. Leschen, #66 ( KNHM).

Paratypes: Peru: 1 male, with same data as holotype, but 5.7.1993 , 3 females, 2. and 3.7.1993 ; 1 male, 1 female, Dept. Loreto, Teniente Lopez (76°06.92'W, 2°35.66'S), 210-240 m elevation, collected by flight intercept trap, 22. and 24.7.1993, leg. R. Leschen ( KNHM, UIC) .

Diagnosis: Among the species of similar size, O. acutus is characterised by the fine punctation of the pronotum, the long acute anterior angles of the pronotum, and the digitate outer edge of the protibia. A similarly digitate outer edge of the protibia is also found in O. longipunctatus and O. guiananus of the O.-guianus -group. But, in these two species the punctation is much coarser and the shape of the pronotum is more trapezoidal, whereas it is smoothly curved in O. acutus . Within the group of the remaining species, O. digitatus has a similarly deep digitate protibia, but the species is smaller with 3.8 mm than O. acutus with 5.1 mm.

Description: Length: 5.1 mm. Colouration: Black; legs dark brown, antennae light brown.

Head: 0.58 mm long, 0.93 mm wide; eyes prominent; distinctly longer than temples; fore-head deeply sinuate; lateral sides of clypeus nearly parallel; anterior edge of clypeus even; angles of clypeus produced to short acute teeth; punctation irregularly dense and deep; without setae; punctation of fore-head finer and sparser than on posterior vertex, but partly granulate; punctation of posterior vertex dense and partly coriaceous; interstices between punctures distinctly shorter than diameter of punctures; on supraocular area punctation coriaceous and striate with few punctures with longer setae; one pair of punctures with long setae on vertex close to neck; area at base of antennae impunctate; fore-head with dense isodiametric microsculpture; vertex with weaker microsculpture and area close to neck without microsculpture.

Antennae nearly as long as head and half of pronotum combined; second antennomere oval; third conical and nearly twice as long as second; following antennomeres increasing in width, but approximately quadrate.

Pronotum: 1.02 mm long, 1.08 mm wide; widest near anterior angles; convergent to posterior angles in smooth curve; in front of posterior angles with short and slight emargination; anterior angles produced to short acute teeth; posterior angles laterally produced to short swollen triangle; lateral margin distinct; in dorsal aspect covered close to anterior angles; widened close to posterior angles; punctation irregularly dense; punctures larger and deeper than on head; on disc, interstices between punctures as wide as diameter of punctures; close to anterior and posterior edges, punctation sparser; irregular and indistinct midline in posterior half impunctate; behind anterior margin and in posterior half with transverse row of setiferous punctures; normal punctures with short setae; between normal punctures with dense micropunctation; weak longitudinal microsculpture; surface slightly shiny.

Elytra: 1.14 mm long, 1.16 mm wide; widest in posterior third, but approximately parallel; shoulders approximately rectangular; punctation much finer than on pronotum; in irregular rows; with deep coriaceous ground-sculpture; surface slightly shiny.

Abdomen on tergites III-VI with sparse and fine punctation, but few larger setiferous punctures; tergites VII and VIII with denser punctation and at least laterally with elongate punctures.

Protibia: 0.54 mm long, 0.15 mm wide; with 8 spines on outer edge; apical spines on long digits; WLR: 0.30; in posterior aspect, inner emargination with comb visible throughout its total length; posterior face sparsely covered by long yellow setae.

Aedeagus angulate in nearly rectangular angle; apical lobe as long as basal lobe; apical lobe shortly narrowed to obtusely rounded apex; laterally close to apex and inner edge with row of sensillae.

Etymology: The specific name acutus derived from the same Latin word meaning acute and refers to the laterally acute posterior angles of the pronotum.

Figures

Fig. 103-108: Remaining-species-group: Osoriellustrinitatis (103), O. carinicollis (104), O. sticticus (105), O. acutus (106), O. orbiculatus (107), O. adustus (108); antenna (A), protibia (B), aedeagus in lateral aspect (C); scale bar: 0.1 mm.