Sacosternum lebbinorum, Fikáček, Martin & Short, Andrew E. Z., 2010

Fikáček, Martin & Short, Andrew E. Z., 2010, A revision of the Neotropical genus Sacosternum Hansen (Hydrophilidae: Sphaeridiinae: Megasternini), Zootaxa 2538, pp. 1-37 : 24-25

Sacosternum lebbinorum sp. n.

(Figs. 5–6, 23–26, 42, 48, 52)

Type locality. Peru, Loreto Region, 160 km NE of Iquitos, Explornapo Camp at Rio Sucusari, 2 km from Rio Napo [coordinates ca. 3°21'S 72°39'W; altitude ca. 100 m a.s.l.].

Type material. Holotype: male ( FSCA): “ PERU: Loreto Pr., 160km / NE Iquitos, Explornapo / Camp, Rio Sucusari, 2 km / from Rio Napo; 27–31- / VIII-1992; P. E. Skelley // Ecitor burchelli / bivoac nearby / litter or soil”. Paratypes (23 spec.): PERU: 15 spec. ( FSCA, KSEM, NHMW, NMPC): same data as holotype. BRAZIL: 1 male, 4 females, 2 spec. ( FMNH, KSEM, NMPC): “ Brazil: Pará, Carajas / March 1984 // from detritus beneath / an ant nest / Coll. by N. Degallier”. FRENCH GUIANA: 1 male, 2 spec. ( KSEM, NMPC): “ FRENCH GUIANA / Roura, 27.4 km SSE, 280 m / 4°44'20"N, 52°13'25"W / 26–29 MAY 1997; J. Ashe, R. Brooks / FG1AB97 0 79 ex: flight intercept trap”.

Additional material examined. 1 male ( FSCA): “Rondonia, 62 / km. SW Ariquemes, nr / Fzda Rancho Grande / 8–20-XI-1994 J. Eger / C. O'Brien; black light”.

Differential diagnosis. Easily recognizable from remaining Sacosternum species by the combination of the large triangular areas at lateral sides of the metaventrite, continually arcuate anterolateral ridge of the metaventrite and drop-like to suboval preepisternal plate of mesothorax. Moreover, S. lebbinorum has only moderately large eyes in comparison with remaining Sacosternum species. For additional differential characters see the key.

Description. Body widest ca at midlength, weakly convex in lateral view. Body length 2.1–2.6 mm (holotype: 2.5 mm), body width 1.1–1.6 mm (holotype: 1.4 mm); TL/TW ratio = 1.8.

Coloration. Dorsal side dark reddish brown; ventral side dark reddish brown; coxae, femora and tibiae dark reddish brown, mouthparts, antennae and tarsi reddish brown.

Head. Clypeus with moderately dense punctation consisting of moderately large circular punctures, each puncture bearing fine decumbent seta; interstices without microsculpture; anterior margin of clypeus slightly concave. Interocular area with triangular area defined by shallow depressions. Frons with moderately dense punctation consisting of moderately large circular punctures; interstices without microsculpture. Eyes moderately large, separated by 4.4× of width of one eye. A tuft of yellowish erect setae anteriorly of each eye absent. Mentum 2.3× wider than long, pentagonal in shape; anteromedian part slightly impressed; surface with sparse punctation consisting of large circular punctures situated only posteriorly; interstices without distinct microsculpture. Maxillary palpomeres 2 and 4 ca. twice as long as palpomere 3. Scapus slightly longer than antennomeres 2–6 combined.

Prothorax. Pronotum slightly more convex than elytra in lateral view, weakly triangular on posterior margin; surface shallowly sulcate, bearing indistinct longitudinal impression posteriorly on each side. Posterolateral corners forming obtuse angle; lateral margin angulate, with wide and distinct lateral rim. Pronotal punctation moderately dense, as dense as that on frons, punctation consisting of moderately large circular punctures; interstices without microsculpture. Transverse row of punctures on posterior margin of pronotum hardly defined. Median carina of prosternum wide but not forming a plate, projecting anteriad mesally, straight in lateral view. Median portion of prosternum 1.6× wider than long; lateral extensions of prosternal shield present; postero-mesal projection with shallow notch. Lateral margin of antennal grooves subangulate.

Mesothorax. Scutellar shield bearing few moderately large punctures, interstices without microsculpture. Elytral series 1–7 arising basally, series 8 arising subbasally; series 9 joining series 8 anteriorly, nearly reaching elytral base. Serial punctures moderately large, transverse, sparsely arranged, much larger than interval punctures. Serial punctures connected to each other by a fine and sharp longitudinal furrow. Elytral intervals moderately convex at suture, becoming slightly more convex laterad and posteriad; series deeply impressed mesally and laterally. Interval punctation arranged in series at least on some intervals, consisting of rather small, transverse scar-like punctures. Epipleura slightly wider than pseudepipleura. Preepisternal plate narrow, 2.1–2.5× longer than wide, drop-like, without median longitudinal carina; median part flat or slightly concave, bearing densely arranged small setiferous punctures, interstices without microsculpture; plate narrowly attached to metaventrite, posterior part slightly overlapping anterior margin of metaventrite.

Metathorax. Metaventrite ca. as long as preepisternal elevation of mesothorax; its median portion indistinctly differing from lateral portion by slightly enlarged punctures. Punctation of median portion of metaventrite consisting of moderately large circular setiferous punctures becoming markedly larger posteriad; interstices without microsculpture, shiny. Anterolateral ridge arcuately bending posteriad towards lateral margin of metaventrite, concave sublaterally. Length of median ridge of metaventrite similar in both sexes, reaching posterior margin of metaventrite. Anterior margin of metaventrite indistinctly crenulate. Lateral portion of femoral line present between anterolateral ridges and lateral sides of metaventrite, delimiting a triangular area. Anepisternum 9.0× longer than wide.

Legs. Protibiae with shallow apical emargination on outer margin.

Abdomen. Ventrite 1 not crenulate anteriorly. Ventrite 2 and 3 with longitudinal ridges, ventrites 4–5 flat; posterior margin of ventrites 1–3 finely denticulate, ventrite 4 finely denticulate or lacking denticles; abdominal ventrite 5 without emargination in both sexes.

Male genitalia. Aedeagus 0.86 mm long. Parameres 1.5× longer than phallobase, rather narrow basally, continually narrowing apicad. Phallobase wide, as long as wide. Median lobe narrow basally, slightly constricted in apical 0.3, slightly widening and continually narrowing apicad. A pair of lateral subapical sclerites absent; apical sclerite wide. Gonopore indistinct. Median portion of sternite 9 shallowly angular.

Variation. Slight variability was observed in the shape and proportions of the preepisternal elevation of mesothorax, which may vary between drop-like to suboval and may be 2.1–2.5× longer than wide. Posterior margin of abdominal ventrite 4 usually lacks denticles; sometimes it bears few isolated denticles and rarely a complete denticulation identical to that on the abdominal ventrite 3 is developed. Aedeagus is rather constant in the structures of the apical portion of the median lobe in all type specimens ( Figs. 23–25 ). The specimen from Ariquemes ( Brazil) mentioned under the additional material examined externally agrees with remaining specimens of S. lebbinorum , but the apical sclerite of its aedeagus is more distinct than in type specimens (in which the basal borders of the sclerite are only vaguely seen even after clearing in KOH) and seems to be narrower apically and more bilobate basally ( Fig. 26 ). We consider these differences as intraspecific variation for the time being.

Etymology. The species is dedicated to fellow Neotropical biologist Dr. Daniel Lebbin and Ms. Erin Allen on the occasion of their marriage.

Biology. Most specimens examined were collected in litter and soil nearby a bivouac of an army ant Eciton burchelli Westwood, 1842 ( Formicidae , Ecitoninae ) or from a detritus beneath an unspecified “ant nest”. Single specimens were collected at light or using flight intercept traps.

Distribution. Confirmed for few widely distributed localities in Peru (Loreto Province), Brazil (Pará Province) and French Guiana. The record from the Brazilian province of Rondonia needs confirmation. Probably widely distributed in northern part of South America.

Figures

FIGURES 23 – 26. Aedeagophores. 23 – 25: S. lebbinorum, holotype; 26: S. cf. lebbinorum from Brazil, Rondonia, SW of Ariquemes. 23: whole aedeagus, dorsal view; 24, 26: detail of the apical portion of the median lobe; 25: detail of apical sclerite after clearing of the aedeagus in KOH.