Sacosternum cruciphallus, 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 : 9-12

Sacosternum cruciphallus sp. n.

(Figs. 9–10, 27, 30)

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

Type material. Holotype: male ( FMNH): “PAN: Chiriqui Prov. / Fortuna, 16-X- 1976 m // FMHD #76- 3002, H. / Wolda”. Paratypes (2 spec.): PANAMA: 2 spec. ( FMNH, NMPC): same locality data as holotype.

Differential diagnosis. Extremely similar to Sacosternum auribleps , S. emissarium and S. garciai by the combination of the absence of triangular areas at the sides of the 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 (complete in S. garciai ) and from all these species by the morphology of the apical portion of the median lobe which is widely expanded and bears very narrow lateral sclerites and very narrow apical sclerite. Females may be distinguished only from S. emissarium based on the posteriorly emarginate abdominal ventrite 5 (entire posteriorly in S. emissarium ).

FIGURES 7–14. Aedeagophores. 7–8: S. auribleps ; 9–10: S. cruciphallus ; 11–12: S. delta ; 13–14: emissarium . 7, 9, 11, 13: whole aedeagus, dorsal view; 8, 10, 12, 14: detail of the apical portion of the median lobe.

Description. Body widest ca at midlength, weakly convex in lateral view. Body length 1.5–1.7 mm (holotype: 1.5 mm), body width 0.9–1.1 mm (holotype: 0.9 mm); TL/TW ratio = 1.7.

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

Head. Clypeus with dense punctation consisting of moderately large rasp-like punctures, each puncture bearing fine decumbent seta; interstices with fine microsculpture; anterior margin of clypeus slightly convex. Interocular area with median triangular area defined by shallow depressions. Frons with moderately dense punctation consisting of moderately large rasp-like punctures; interstices with fine mesh-like microsculpture. Eyes large, separated by 1.7× of width of one eye. A tuft of yellowish erect setae anteriorly of each eye absent. Mentum 1.4× wider than long, anterior margin slightly emarginate, anteromedian part slightly impressed, bearing sparse punctation consisting of large nearly circular punctures; interstices with fine mesh-like microsculpture. Maxillary palpomere 2 and 4 ca. twice as long as palpomere 3. Scapus slightly longer than antennomeres 2–6 combined.

Prothorax. Pronotum forming continuous curve with elytra in lateral view, continuously arcuate on posterior margin, shallowly sulcate sublaterally, bearing two (rarely three) weak but distinct longitudinal impressions. Posterolateral corners rounded; lateral margin weakly sinuate with narrow marginal rim. Pronotal punctation moderately dense, ca. as dense as that on frons; punctation consisting of rather large deeply impressed 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 prosternal shield not developed; posteromesal projection with shallow notch. Lateral margin of antennal grooves rounded.

Mesothorax. Scutellar shield without 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 small, transverse, sparsely arranged, ca. as large as interval 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 weakly impressed mesally and laterally. Interval punctation arranged in series at least on some intervals, consisting of small, transversely scar-like punctures. Epipleura ca. as wide as pseudepipleura. Preepisternal plate very narrow, suboval, 3.3× longer than wide; median part slightly concave bearing densely arranged large setiferous punctures, interstices without microsculpture; median longitudinal carina absent; preepisternal elevation narrowly attached to metaventrite, its 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 moderately dense, consisting of rather large nearly circular setiferous punctures; interstices without microsculpture, shiny. Anterolateral ridge arcuately bent posteriad along lateral margin, 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 portions of femoral lines absent, triangular area at lateral sides of metaventrite absent. Anepisternum 8.8× longer than wide.

Legs. Protibiae not emarginate on outer margin apically.

Abdomen. Abdominal 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 emarginate medially in females.

Male genitalia. Aedeagus 0.63 mm long. Parameres 1.5× longer than phallobase, wide basally, gradually narrowing apicad. Phallobase wide, 0.9× longer than wide. Median lobe nearly parallel-sided in basal 0.6, strongly widened in apical 0.4. A pair of lateral subapical sclerites present; apical sclerite narrow; lateral sclerites very narrow and long, in almost perpendicular position to apical sclerite. Gonopore present, situated subapically. Median portion of sternite 9 shallowly circular.

Variability. None observed.

Etymology. Derived from crux (Lat., cross) and phallos (Greek, penis), reflecting the cross-shaped arrangement of the sclerites in the apical part of the median lobe of this species. Standing as a noun in apposition.

Biology. Unknown.

Distribution. Known only from the type locality.