Sacosternum megalopus Hansen, 1989

Fikáček, Martin & Short, Andrew E. Z., 2010, A revision of the Neotropical genus Sacosternum Hansen (Hydrophilidae: Sphaeridiinae: Megasternini), Zootaxa 2538, pp. 1-37 : 25-28

Sacosternum megalopus Hansen, 1989

(Figs. 21–22, 28, 32)

Type locality. Panama, Chiriquí Province, Fortuna [coordinates ca. 8°43'N 82°15'W; altitude ca. 1100 m a.s.l.].

Type material examined: Holotype: male ( UCDC): “ Fortuna PAN / Chirique Prov. / IX-12-1977 / Henk Wolda // HOLOTYPE / Sacosternum / megalopus / M. Hansen”. Paratype: 1 spec. ( UCDC): same locality as holotype but with date “ IV-20-1979 ” and type label “ PARATYPE / Sacosternum / megalopus / Hansen”.

Note. The second paratype from Boquete ( Panama) was not examined for this study and we cannot therefore reconfirm its assignment to S. megalopus .

Additional material examined: COSTA RICA: 1 female ( INBio): “ COSTA RICA: Prov. Puntarenas, Coto / Brus, Estación Pittier, 1680 m. 01–13 Oct / 2000 R. Gonzales Manual L_S / _578645_330030 #59656”; 1 spec. ( KSEM, pure alcohol collection of A. Short): “ COSTA RICA: Cartago Province / Tapantí National Park / 09°45.671'N / 83°47.087'W / 1276 m, H-G vapor light, 7.i.2004 / AEZ Short leg. AS-04-009”.

Differential diagnosis. The species may be very easily recognized from all remaining Sacosternum species by the presence of a small tuft of erect setae in from of each eye (seemingly forming small horns) and by abdominal ventrite 5 bearing very distinct longitudinal ridges. Both these characters are absent from all other known species. See the identification key for further diagnostic characters.

Redescription. Body widest ca at midlength, weakly convex in lateral view. Body length 2.1–2.2 mm (holotype: 2.1 mm), body width 1.2–1.3 mm (holotype: 1.3 mm); TL/TW ratio = 1.7.

Coloration. Dorsal side reddish brown, frons at eyes dark brown; ventral side reddish brown; legs, mouthparts and antennae reddish brown.

Head. Clypeus with moderately dense punctation consisting of rather small semicircular rasp-like punctures, each puncture bearing fine decumbent seta; interstices without microsculpture; anterior margin of clypeus slightly convex. Interocular area with triangular area defined by shallow depressions. Frons with moderately dense punctation consisting of rather small semicircular rasp-like punctures; interstices without microsculpture. Eyes large, separated by 1.3× of width of one eye. A tuft of yellowish erect setae anteriorly of each eye present. Mentum 1.8× wider than long, anterior margin slightly emarginate, anteromedian part slightly impressed; surface with sparse punctation consisting of 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 forming continuous curve with elytra in lateral view, weakly bisinuate on posterior margin; surface shallowly sulcate, bearing two weak but distinct longitudinal impressions sublaterally on each side. Posterolateral corners rounded; lateral margin arcuate, with wide and distinct lateral rim. Pronotal punctation dense, as dense as that on frons, consisting of larger small, semicircular rasp-like 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 1.2× wider than long; lateral extensions of prosternal shield absent; postero-mesal projection with shallow notch. Lateral margin of antennal grooves rounded.

Mesothorax. Scutellar shield bearing few minute punctures, interstices with fine mesh-like microsculpture. Elytral series 1–5 and 7 arising basally, series 6 slightly subbasally, series 8 distinctly 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 more convex laterad and posteriad; series deeply impressed mesally and laterally. Interval punctation arranged to series at least on some intervals, consisting of small, transversely scar-like punctures. Epiplerua ca. as wide as pseudepipleura. Preepisternal plate very narrow, 4.0× longer than wide, suboval, median part flat, bearing densely arranged moderately large 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 markedly differing from lateral portion in punctation and microsculpture. Punctation of median portion of metaventrite absent (with exception of few minute punctures laterally); 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 lines and triangular area at lateral sides of metaventrite absent. Anepisternum 9.1× longer than wide.

Legs. Protibiae not emarginate on outer margin apically.

Abdomen. Ventrite 1 not crenulate anteriorly. Ventrites 2–5 with longitudinal ridges; posterior margin of ventrites 1–4 finely denticulate; abdominal ventrite 5 without emargination in both sexes.

Male genitalia. Aedeagus 0.74 mm long. Parameres 1.4× longer than phallobase, rather wide basally, continually narrowing apicad. Phallobase as long as wide. Median lobe narrow throughout the length except of the apparent widening in apical 0.3. A pair of indistinct lateral subapical sclerites present. Gonopore present, situated subapically. Median portion of sternite 9 shallowly circular.

Variation. None observed.

Biology. Unknown. Non-type specimens examined were collected at light and by manual collecting.

Distribution. Known from three relatively closely situated localities in the mountains that straddle Costa Rica (Puntarenas and Cartago Provinces) and Panama (Chiriquí Province).