Oosternum holosericeum Hebauer & Hansen, 2009, sp. n.
Creators: name: Hebauer, Martin Fiká Č Ek Franz
name: Hansen, Michael
Publisher: name: Zenodo
Year: 2009
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Hydrophilidae
Oosternum
Oosternum holosericeum

description: Oosternum holosericeum sp. n.
(Figs. 34, 37, 47, 58–59, 65, 71, 77, 81, 83, 84)
Type locality: Argentina, Salta province, 11.2 km N of La Caldera, 1550m.
Type material: Holotype. 1 male (CMN): “ARG:SaltaProv, 17kmN La / Caldera, AltodelaSierra / 1550m, 2.–30.XII.87 / S&JPeck, malaise-FIT / subtrop. humid forest”. Paratypes (26). 6 unsexed specimens (CMN, KSEM, NMPC): same data as holotype; 14 unsexed specimens (BMNH, CMN, KSEM, MACN, NMPC): “ARG:SaltaProv. 22kmN / La Caldera, 1550m / El Ucumar, S&JPeck / 2–30.XII.87, malaise-FIT / subtropical humid forest”; 3 unsexed specimens (CMN, MACN): “ARG: SaltaProv. / ElReyNat.Park, 1000m / PozoVerdeTrail, 7 km / 5–15.XII.87, S&JPeck / Mal.-FIT, Yungas for.”; 1 unsexed specimen (CMN): “ARG: SaltaProv. / El Rey Nat. Park, 1200m / PozoVerdeTrail, km10 / 10.XII.87, S&JPeck / forest, fungi on logs”.
Differential diagnosis: Body widest at midlength; pronotum weakly convex; pronotal punctation moderately dense, consisting of scar-like punctures; pronotal interstices with microsculpture; median carina of prosternum without anterior tooth; preepisternal elevation of mesothorax 2.0× longer than wide; median portion of metaventrite with intersticial microsculpture; eyes large, separated by 5.0× of one eye; parameres without inner projections; lateral projections of median lobe narrow, developed in apical 0.45 of median lobe.
The species is characterized by microsculptured (and therefore dull) pronotum and elytra, dark coloration (Fig. 34), weakly convex pronotum and elongate oval body (Fig. 37). It can be confused only with O. aequinoctiale, which is however usually paler, lacks microsculpture on elytra and mesal part of median elevation of metaventrite and is characterized by pronotum “bumpy” along posterior margin (this “bumpy” appearance is not developed in O. holosericeum). O. holosericeum is moreover characteristic by highly elevate median longitudinal carina of prosternum and can be easily distinguished from O. aequinoctiale by male genitalia (inner projections of parameres are missing in O. holosericeum, but very large in O. aequinoctiale; compare Figs. 46 and 47).
Description. HABITUS: Body elongate oval, widest ca at midlength, moderately convex in lateral view, gradually narrowing posteriad; TL/TW ratio = 1.7. Length: 1.45–1.85 mm, length of HT: 1.60 mm; width: 0.85–1.10 mm, width of HT: 0.95 mm.
COLORATION. Coloration of dorsal side pitchy brown to black, anterior margin of clypeus, margins of pronotum and lateral margins of elytra brown. Ventral side pitchy brown to black, median part of prosternum and head brown. Legs with pitchy brown coxae, brown tibiae and reddish tarsi, mouthparts and antennomeres 1–7 reddish, antennomeres 8–9 brown.
HEAD. Clypeus with dense punctation consisting of fine, shallow round punctures, each puncture bearing fine decumbent yellowish seta; interstices with fine microsculpture; anterior margin slightly concave. Frons with moderately dense punctation, consisting of small sharply impressed, slightly scar-like punctures, punctures of same shape medially and laterally; interstices with fine mesh-like microsculpture. Eyes large, separated by 5.0× of width of one eye. Mentum 2.0× wider than long, anterior margin slightly emarginate; punctation consisting of large, sharply impressed round punctures bearing minute setae; interstices with very fine microsculpture, opaque. Submentum without poriferous disc-like eara. Maxillary palpus with palpomeres 2 and 4 ca. 1.5× longer than palpomere 3. Scapus ca. as long as antennomeres 2–6 combined; antennal club ca. 2.2× longer than wide.
PROTHORAX. Pronotum slightly more convex than elytra, punctation consisting of moderately large, sharply impressed, slightly scar-like punctures, similar on whole surface of pronotum; interstices with microsculpture. Median carina of prosternum straight in lateral view. Median portion of prosternum as wide as long, postero-mesal projection with shallow notch, pits laying next to ridges delimiting prosternal plate moderately large.
MESOTHORAX. Scutellar shield bearing a few minute punctures, interstices with fine mesh-like microsculpture. Elytral series 1–8 arising basally, series 9 nearly reaching elytral base. Elytral series 7 and 8 as widely separated from each other as other series. Serial punctures fine and sparse. Elytral intervals weakly convex at suture; intervals 5, 7 and 9 hardly more convex than adjacent intervals; punctation arranged to series at least on some intervals, consisting of very fine scar-like punctures. Elytral interstices opaque, with fine microsculpture. Epipleuron narrowing posteriad, reaching elytral apex. Preepisternal plate suboval, 2 longer than wide; median part flat, bearing densely arranged, moderately large, sharply impressed round setiferous punctures; interstices with very fine microsculpture, opaque.
METATHORAX. Punctation of median portion of metaventrite moderately dense, consisting of large, sharply impressed, round setiferous punctures; interstices with strong mesh-like microsculpture on the whole surface. Anepisternum 7.4× longer than wide.
LEGS. Tarsi with long yellowish pubescence ventrally.
ABDOMEN. Ventrite 1 with additional longitudinal ridges laterally.
MALE GENITALIA. Paramere 1.3× longer than phallobase, without inner projection, bearing two long setae apically. Phallobase narrow, 1.8× longer than wide. Median lobe slightly narrowing from base to obtusely pointed apex; lateral projections narrow, developed in apical 0.5 of median lobe.
Variation. Except for the slight size and color variability described above, the species varies slightly also in the microsculpture of the median part of the metaventrite. In some specimens, the microsculpture is rather reduced medially (but still very strongly developed at sides of median elevation) and median part the median elevation of the metaventrite seems therefore more shiny than in typical specimens.
Etymology. Latin holosericeus = silky, the name refers to a silk luster of the elytra characteristic for this species.
Habitat. Most of the species were collected by FIT/Malaise traps in subtropical humid and yungas (= subtropical moist broadleaf) forests. One specimen was found on fungi on logs.
Distribution. Northeastern part of Argentina (Salta Province) at altitudes 1000-1500 m a.s.l.
Remarks. Based on information by S. Peck, the type locality is situated near the road between Salta and San Salvador de Jujuy 17 km N of La Caldera via road (in valley bottom forest, 1 km down from road crew camp, first patch of forest along road going north from La Caldera). Based on this specification, the locality should be situated ca. 11.2 km N of La Caldera ca. at the following coordinates: 24°30΄S 65°21΄W.
description: Published as part of Hebauer, Martin Fiká Č Ek Franz & Hansen, Michael, 2009, Taxonomic revision of New World species of the genus Oosternum Sharp (Coleoptera: Hydrophilidae: Sphaeridiinae) I. Definition of species groups and revision of the Oosternum aequinoctiale group, pp. 1-37 in Zootaxa 2054 on pages 30-31, DOI: 10.5281/zenodo.186668