Sacosternum emissarium, 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 : 13-14

Sacosternum emissarium sp. n.

(Figs. 13–14, 51)

Type locality. Costa Rica, Puntarenas Province, Coto Brus Canton, Estación Pittier, 1670 m a.s.l. [coordinates ca. 9°04'N 82°56'W].

Type material. Holotype: male ( INBio): “ COSTA RICA: Prov. Puntarenas, Coto / Brus, Estación Pittier, 1670m, 22 ENE / 2000. R. Gonzales. Red de Golpe / L_S_330030_578645 #56804”. Paratypes (3 spec.): COSTA RICA: 1 female ( KSEM): “ COSTA RICA: Prov. Puntarenas, Coto / Brus, Estación Pittier, 1670m, 20 ENE / 2000. R. Gonzales. Mantillo / L_S_330030_578645 #56805”; 1 spec. ( NMPC): “ COSTA RICA: Prov. Puntarenas, Coto / Brus, Estación Pittier, 1670m, 18 ENE / 2000. R. Gonzales. Mantillo / L_S_330030_578645 #56368”; 1 spec. ( INBio): “ COSTA RICA: Prov. Puntarenas, Coto / Brus, Estación Pittier, 1670m, 30 / NOV-12 DIC 1999. R. Gonzales de / Luz L_S_330030_578645 #57372”.

Differential diagnosis. Extremely similar to Sacosternum auribleps , S. cruciphallus and S. garciai by the combination of the absence of triangular areas at the sides of metaventrite, very narrow preepisternal plate of mesothorax, pronotum with fine microsculpture and two very distinct sublateral longitudinal impressions. Males may be distinguished from S. garciai by the posteriorly reduced median carina of metaventrite (reaching posterior margin of metaventrite in S. garciai ) and from all these species by the very wide aedeagus and the morphology of the apical portion of the median lobe which is widely expanded and bears wide apical as well as lateral sclerites. Females may be distinguished from all above species by the absence of an emargination of abdominal ventrite 5 (present in the remaining species of " S. cruciphallus complex").

Description. Body widest ca at midlength, weakly convex in lateral view. Body length 1.6–1.7 mm (holotype: 1.7 mm), body width 1.0– 1.1 mm (holotype: 1.0 mm); TL/TW ratio = 1.6.

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

Head. Clypeus with dense punctation consisting of moderately large rasp-like punctures without setae; interstices with fine microsculpture; anterior margin of clypeus slightly convex. Interocular area with median triangular area defined by shallow depressions. Frons with dense punctation consisting of moderately large rasp-like punctures; interstices with fine mesh-like microsculpture. Eyes large, separated by 2.4× of width of one eye. A tuft of yellowish erect setae anteriorly of each eye absent. Mentum 2.3× wider than long, anterior margin slightly emarginate, anteromedian part slightly impressed; surface with sparse punctation consisting of large nearly circular punctures, interstices with fine mesh-like microsculpture. Maxillary palpomeres 2 and 4 ca. twice as long as palpomere 3. Scapus slightly longer than antennomeres 2–6 combined.

Prothorax. Pronotum continuously arcuate on posterior margin, forming continuous curve with elytra in lateral view, shallowly sulcate, bearing two weak but distinct longitudinal impressions on each side. Posterolateral corners rounded, lateral margin weakly sinuate, with narrow marginal rim. Pronotal punctation moderately dense, slightly denser than that on frons, consisting of moderately large rasp-like punctures; interstices with 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 1.3× wider than long; additional lateral expansions of the prosternal shield not developed; postero-mesal projection with shallow notch. Lateral margin of antennal grooves rounded.

Mesothorax. Scutellar shield bearing few moderately large circular punctures, interstices with fine meshlike 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 small, transverse, sparsely arranged, ca. as large as 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 weakly impressed mesally and laterally. Interval punctation arranged to series at least on some intervals, consisting of small, transversely scar-like punctures. Epipleura ca. as wide as pseudepipleura. Preepisternal plate very narrow, 4.8× longer than wide, suboval, flat, bearing densely arranged large setiferous punctures; plate narrowly attached to metaventrite, posterior part slightly overlapping anterior margin of metaventrite.

Metathorax. Metaventrite ca. as long as preepisternal elevation of mesothorax; median portion markedly differing from lateral portion in punctation and microsculpture. Punctation of median portion consisting of small, circular setiferous punctures; interstices without microsculpture, shiny. Anterolateral ridge arcuately bending posteriad towards lateral margin of metaventrite, concave sublaterally. Length of median ridge of metaventrite sexually dimorphic, reaching anterior third of metaventrite length in male and posterior margin of metaventrite in female. Anterior margin of metaventrite indistinctly crenulate. Lateral portion of femoral lines absent, triangular area at lateral sides of metaventrite absent. Anepisternum 9.8× longer than wide.

Legs. Protibiae not emarginate on outer margin apically.

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 without emargination in both sexes.

Male genitalia. Aedeagus 0.73 mm long. Parameres 1.2× longer than phallobase, wide basally, slightly narrowing apicad. Phallobase as long as wide. Median lobe narrow basally, markedly widened in apical fifth. A pair of lateral subapical sclerites present; apical sclerite wide; lateral sclerites wide, semicircular, in almost perpendicular position to apical sclerite. Gonopore present, situated subapically. Median portion of sternite 9 shallowly circular.

Variation. None observed.

Etymology. Derived from emissarius (Lat., spy, scout) reflecting the large eyes typical for Sacosternum and the shape of the sclerites in the apical portion of the median lobe resembling the lily-flower symbol of scouting movement. Treated as an adjective.

Biology. Unknown. Specimens examined were collected at light, using flight intercept trap and (probably sifted) from humus.

Distribution. Known only from the type locality.