Oosternum acutheca, Hebauer, Martin Fiká Č Ek Franz & Hansen, Michael, 2009

Hebauer, Martin Fiká Č Ek Franz & Hansen, Michael, 2009, Taxonomic revision of New World species of the genus Oosternum Sharp (Coleoptera: Hydrophilidae: Sphaeridiinae) I. Definition of species groups and revision of the Oosternum aequinoctiale group, Zootaxa 2054, pp. 1-37 : 13-16

Oosternum acutheca sp. n.

(Figs. 38, 42, 48–49, 60, 66, 72, 84)

Type locality: Honduras, Olancho province, La Muralla National Park, 14 km N of La Union, 1450 m a.s.l.

Type material: Holotype. 1 male ( CMN): “ HONDURAS: OLANCHO / La Muralla N.P., 14 km N. / La Union, 1450m, 25. VI. / 1994 – 130A, R. Anderson / mont. wet evergr. for. litt.”. Paratypes (155): COSTA RICA: 1 male, 1 unsexed spec. ( KSEM): “ COSTA RICA: Alajuela / 14 km S. Volcan Arenal / 10°20'N, 84°43'W, 1000m // ex., sifted leaf litter / 29 April 1988 / John Longino #2037-S”; 1 unsexed spec. ( KSEM): “ COSTA RICA: Puntarenas / Monte Verde, 1240m / 10 May 1989, J. Ashe, / R. Brooks, R. Leschen // ex., berlese of upper / streambed, in sand // Snow Entomol. Mus. / Costa Rica Exped #95”; 2 males, 48 unsexed specimens ( BMNH, CNC, NHMW, NMPC, ZMUC): “ COSTA RICA: Guanacaste P / Guanacaste Cons. Area / Cacao Field Stn., 1200m / 12.Feb.1996 R. Anderson / wet montane forest litter”; 30 unsexed specimens ( HHFU, NMPC, SRBC, ZMUC): “ COSTA RICA: Guanacaste P / Guanacaste Cons. Area / Cacao Field Stn., 1250m / 20.Feb.1996 R. Anderson / wet montane forest litter”; 1 male, 25 unsexed specimens ( KSEM, NMPC): “ COSTA RICA: Guanacaste / Cacao Biol. Station, 1100–1200M / 10°56'0"N, 85°27'0"W / 4 MAY 1995; R. Anderson / CR1A95 3A [in some specimens also 3B, 3C, 3D or 3E] berlese leaf litter”; 1 male, 4 unsexed specimens ( KSEM, NMPC): “ COSTA RICA: Guanacaste / Pitilla Biological Station, 600 m / 10°58'0"N, 85°25'0"W, / 2 MAY 1995; R. Anderson / CR1A95 4B berlese leaf litter”; 1 unsexed specimen ( FMNH): “ COSTA RICA: Guanacaste; / Canas, Miravalles Volcano / 10°42'N – 85°7'W; IV:8:1973 / leg. J. Wagner, J. Kethley // FM(HD) #73-384 / 73CRIV-8d Berlese / 4 liters conc. log mold / on slope”; 1 male, 1 female ( FMNH): “ COSTA RICA: Heredia: OTS / LaSelva field Sta., Puerto / Viejo de Sarapiquí, Rio / Puerto Viejo, III:7:1973 / 10°26'N – 83°59'W / leg. J. Wagner, J. Kenthley // FM(HD) #73-273 / 73CR-III-7b LS Ber. / conc. 2m 2 floor litter / on slope, 100 cc. virgin for.”. HONDURAS: 1 female, 1 unsexed specimen ( CMN): “ HONDURAS: OLANCHO / P. N. La Muralla, 14 km N. / La Union, 1430m, 16–17.VIII. / 1994 – 208, R. Anderson / liquidambar/oak for. litt. berl.”; 8 unsexed spec. ( CMN, KSEM, NMPC): “ HONDURAS: OLANCHO / P. N. La Muralla, 14 km N La / Union, 1450m / 16–17.VIII. / 1994 – 207, R. Anderson, mont. / wet evergreen forest litt. berl.”; 11 unsexed specimens ( BMNH, CNC, KSEM, NHMW, NMPC): “ HONDURAS: Olancho / La Muralla, 14 km N. La / Union, 1450m, 25.VI.1994 / 15°06'N, 86°42'W / Anderson #130, ex: wet / montane everg. litter”. NICARAGUA: 2 males, 16 unsexed specimens ( KSEM, NMPC): “ NICARAGUA: MATAGALPA / 6 km N Matagalpa Selva Negra / 1500m, N12°59.9΄ W85°54.6΄ / 21.V.2002, R. Anderson, ridge- / top cloud for. litter, 2002-026”.

Additional material examined (1): 1 male ( KSEM): “ COSTA RICA: Alajuela / Peñas Blancas, 850m / 18 May 1989, J. Ashe // R. Brooks, R. Leschen / ex., sifted liter [sic!] along / stream / Snow Entomol. Mus. / Costa Rica Exped. #236 / larvae in EtOH Coll. n.”

Differential diagnosis: Body widest at junction of pronotum and elytra; pronotum highly convex; pronotal punctation dense, consisting of sharply impressed rasp-like punctures; pronotal interstices lacking microsculpture; median carina of prosternum without anterior tooth; preepisternal elevation of mesothorax 1.3× longer than wide; median portion of metaventrite without intersticial microsculpture; eyes small, separated by 8.5× of one eye; mentum without mesh-like microsculpture; parameres with moderately large inner projections; lateral projections of median lobe wide, developed only in apical 0.35 of median lobe.

The species is easily recognizable especially by its highly convex pronotum lacking microsculpture but bearing very densely arranged punctures (Figs. 38, 48–49). It is very similar to O. attenuatum , from which it can be recognized by characters given in the key (see under O. attenuatum for more details). The species also resembles O. gibbicolle from which it is easily recognizable by rasp-like pronotal punctures (punctures are ring-like in O. gibbicolle ) and different male genitalia (lateral projections of median lobe are wide and short and inner projections of parameres are moderately developed in O. acutheca ).

Description: HABITUS: Body widely oval, widest on base of elytra, highly convex in lateral view, strongly narrowing posteriad; TL/TW ratio = 1.5. Length: 1.25–1.50 mm, length of HT: 1.25 mm; width: 0.85–1.00 mm, width of HT: 0.85 mm.

COLORATION. Coloration of dorsal side brown to dark brown, elytra slightly darker than prontum and head, clypeus ferrugineous. Ventral side brown, mentum rusty brown. Femora, tibiae and antennal club reddish brown, tarsi, mouthparts and antennomeres 1–6 yellowish.

HEAD. Clypeus with dense punctation, consisting of coarse, rounded, sharply impressed punctures becoming slightly smaller and rasp-like on anterior margin, each puncture bearing fine decumbent yellowish seta; interstices without microsculpture; anterior margin slightly concave. Frons with dense punctation, consisting of coarse, sharply impressed, rounded punctures, punctures of same shape medially and laterally; interstices without microsculpture. Eyes small, separated by 8.5× of width of one eye. Mentum 2.4× wider than long, anterior margin deeply emarginate; punctation consisting of large, sharply impressed semicircular setiferous punctures bearing long setae posteriorly; interstices without distinct microsculpture. Submentum with poriferous disc-like ereas. Maxillary palpus with palpomeres 2 and 4 ca. 1.5× longer than palpomere 3. Scapus shorter than antennomeres 2–6 combined; antennal club ca. 2× longer than wide.

PROTHORAX. Pronotum apparently more convex than elytra, punctation consisting of slightly rasp-like, sharply impressed punctures, similar on whole surface of pronotum; interstices without microsculpture. Median carina of prosternum straight in lateral view. Median portion of prosternum 1.3× wider than long, postero-mesal projection with shallow notch, pits laying next to ridges delimiting prosternal plate minute.

MESOTHORAX. Scutellar shield bearing a few small, rap-like punctures, interstices without microsculpture. Elytral series 1–6 arising basally, series 7–8 joint subbasally, series 9 abbreviated anteriorly, undetectable in ca. basal 0.2. Elytral series 7 and 8 markedly closer to each other than to other series. Serial punctures fine, rather dense. Elytral intervals weakly convex at suture; intervals 5, 7 and 9 hardly more convex than adjacent intervals; punctation irregular on all intervals, consisting of sparsely arranged minute, scar-like punctures. Elytral interstices shiny, without microsculpture. Epipleuron narrowing posteriad, reaching elytral apex. Preepisternal plate drop-like, 1.3× longer than wide; median part flat, bearing densely arranged, rasp-like, sharply impressed setiferous punctures; interstices without microsculpture.

METATHORAX. Punctation of median portion of metaventrite consisting of sharply impressed, slightly rasp-like setiferious punctures, large mesally and slightly smaller laterally, interstices without microsculpture, shiny. Anepisternum 6.8× longer than wide.

LEGS. Tarsi with short and sparse pubescence ventrally.

ABDOMEN. Ventrite 1 without additional longitudinal ridges laterally.

MALE GENITALIA. Paramere 1.3× longer than phallobase, with moderately large inner projection, bearing two short setae apically. Phallobase narrow, 1.4× longer than wide. Median lobe gradually narrowing from base to apex; lateral projections large, developed in apical 0.35 of median lobe.

Variation. The species varies slightly in the shape of the preepisternal plate, which is rarely as narrow as in the remaining species of the O. aequinoctiale species group. Precise shapes of lateral projections of median lobe and inner projections of parameres also slightly vary among specimens.

Etymology. Latin acutheca = pin-cushion, the name refers to the bumpy convex shape of pronotum bearing numerous punctures resembling pin punctures. To be treated as a noun in apposition.

Habitat. Most of the type specimens were sifted from wet leaf litter in evergreen montane forests.

Distribution. Distributed in Central America at altitudes 600–1500 m a.s.l. Known from Costa Rica (Alajuela, Guanacaste, Heredia, and Puntarenas Provinces), Honduras (Olancho Province) and Nicaragua (Matagalpa Province).