Sacosternum delta, 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 : 12-13

Sacosternum delta sp. n.

(Figs. 11–12, 29, 44, 54)

Type locality. Paraguay, Itapúa Department, Yalai, San Rafael Reserve, 26°38'17"S 55°39'50"W, 100 m a.s.l.

Type material. Holotype: male ( KSEM): “ PARAGUAY: Itapúa / Yalai, prop. Hostettier family / San Rafael Reserve, 100 m / 26°38'17"S, 55°39'50"W / 25–26 NOV 2000; Z.H. Falin / PAR1F00 048A / ex: flight intercept trap”. Paratype (1 spec.): BRAZIL: 1 female ( FSCA): “ BRAZIL: Rondonia, 62 / km. SW Ariquemes, nr. / Fzda. Rancho Grande / 8–20-XI-1994; J. Eger, / C. O'Brien; black light”

Differential diagnosis. Differs from all known Sacosternum species except S. inconnivum by the shape of the anterolateral ridge on the metaventrite, which is angulate sublaterally. It may be distinguished from the latter species by median prosternal carina which is straight in lateral view (in contrast to slightly elevated in S. inconnivum ). Males may be distinguished from the latter species by a very narrow aedeagus and the apical portion of median lobe without triangularly narrowed sclerotized median portion. Females may be distinguished from the latter species by the posteriorly emarginate abdominal ventrite 5 (in contrast to the entire ventrite 5 in females of S. inconnivum ).

Description. Body widest ca. at midlength, weakly convex in lateral view. Body length 1.7–2.0 mm (holotype: 1.7 mm), body width 1.1–1.3 mm (holotype: 1.1 mm); TL/TW ratio = 1.65.

Coloration. Dorsal side reddish brown; ventral side reddish brown; legs, mouthparts and antennae reddish brown.

Head. Clypeus with moderately dense punctation consisting of moderately large semicircular, slightly rasp-like punctures, each puncture bearing fine decumbent seta; interstices without microsculpture; anterior margin of clypeus truncate. Interocular area with median triangular area defined by shallow depressions. Frons with moderately dense punctation consisting of moderately large semicircular, slightly rasp-like punctures; interstices without microsculpture. Eyes large, separated by 2.8× of width of one eye. A tuft of yellowish erect setae anteriorly of each eye absent. Mentum 1.8× wider than long, anterior margin slightly emarginate, anteromedian part slightly impressed; surface with dense punctation consisting of rather large circular punctures; interstices without distinct microsculpture. Maxillary palpomeres 2 and 4 ca. 1.5× as long as palpomere 3. Scapus slightly longer than antennomeres 2–6 combined.

Prothorax. Pronotum slightly more convex than elytra in lateral view, weakly bisinuate on posterior margin; surface evenly convex or shallowly sulcate laterally, bearing indistinct sublateral longitudinal impression posteriorly on each side; posterolateral corners forming obtuse angle, lateral margin arcuate or slightly angulate, with narrow marginal rim. Pronotal punctation moderately dense, slightly denser than on frons, consisting of moderately large, rounded, rather sharply impressed punctures; interstices without microsculpture. Transverse row of punctures on posterior margin of pronotum absent. Median carina of prosternum narrow, projecting anteriad mesally, straight in lateral view. Median portion of prosternum 0.7× wider than long; additional lateral expansions of prosternal shield well developed; posteromesal projection with shallow notch. Lateral margin of antennal grooves subangulate.

Mesothorax. Scutellar shield bearing few moderately large circular punctures, interstices without microsculpture. Elytral series 1–5 and 7 arising basally, series 6 and 8 arising subbasally; series 9 joining series 8 anteriorly, nearly reaching elytral base. Serial punctures large, rounded, sparsely arranged, much larger than interval punctures. Serial punctures connected to each other by a fine and sharp longitudinal furrow. Elytral intervals weakly convex at suture, becoming slightly more convex laterad and posteriad; series deeply impressed mesally and laterally. Punctation irregular on all intervals, consisting of small, scar-like punctures. Epipleura ca. as wide as pseudepipleura. Preepisternal plate narrow; 1.8× longer than wide, arrowhead shaped with median longitudinal carina, bearing rather dense and coarse setiferous punctation; the plate widely attached to metaventrite, its posterior part slightly overlapping over anterior margin of metaventrite,

Metathorax. Metaventrite ca. as long as preepisternal elevation of mesothorax, with median portion markedly differing from lateral portion in punctation and microsculpture. Punctation of median portion of metaventrite consisting of densely arranged, moderately large circular setiferous punctures; interstices without microsculpture, shiny. Lateral portions of anterolateral ridges bending posteriad towards lateral margin of metaventrite, with sharp angle sublaterally. Length of median ridge of metaventrite sexually dimorphic, reaching posterior fifth in male and posterior margin of metaventrite in female. Anterior margin of metaventrite crenulate. Lateral portion of femoral lines developed between anterolateral ridge and margin of metaventrite, delimiting a triangular area at lateral portions of metaventrite. Anepisternum 8.2× longer than wide.

Legs. Protibiae with shallow apical emargination on outer margin.

Abdomen. Ventrite 1 not crenulate anteriorly. Ventrites 2–4 with longitudinal ridges, ventrite 5 flat; posterior margin of ventrites 1–4 finely denticulate; abdominal ventrite 5 weakly emarginate medially in females.

Male genitalia. Aedeagus 0.75 mm long. Parameres 1.1× longer than phallobase, narrow, gradually narrowing apicad. Phallobase narrow, 1.5× longer than wide. Median lobe narrow in basal 0.7, slightly widened in apical 0.3 and then narrowing apicad. A pair of lateral subapical sclerites absent; apical sclerite narrow. Gonopore present, situated subapically. Median portion of sternite 9 shallowly circular.

Variation. Only a slight variation in the depth of the lateral impressions of the pronotum was observed between the two specimens examined.

Etymology. Derived from delta , the Greek letter shaped as a triangle, referring to the large triangular area on the lateral portion of metaventrite typical for this species. Standing as a noun in apposition.

Biology. Unknown. The holotype was caught in flight intercept trap.

Distribution. Known from one locality in western Brazil and one locality in southern Paraguay.