Oosternum convexum, Fikáček & Hebauer, 2009

Fikáček, Martin & Hebauer, Franz, 2009, Taxonomic revision of the New World species of the genus Oosternum Sharp (Coleoptera: Hydrophilidae: Sphaeridiinae) II. The Oosternum convexum species group, Acta Entomologica Musei Nationalis Pragae 49 (1), pp. 103-117 : 109-110

Oosternum convexum sp. nov.

( Figs. 1, 2 , 7–9, 11, 14 , 17, 19, 22–24 )

Type locality. Panama, Chiriqui Province, 4.5 km SE of Cerro Punta, oak and bamboo forest.

Type material. HOLOTYPE: J ( CNC): ‘PAN. Chiriqui , 4.5 / km SE Cerro Punta / oak & bamboo forest / 28.V.1977 / S&J Peck’ . PARATYPES (205 spec.): PANAMA: 11 spec. ( CNC, ZMUC, NMPC): same data as holotype ; 1J ( ZMUC): ‘PAN., Chiriqui, 1700m / 2km. W. Cerro Punta / 24.-28.V.77 S. & J. / Peck. Ber. 376 / litter & carrion’ ; 1 J, 37 spec. ( ZMUC, BMNH, FEFU, NHMW, NMPC, SRBC): ‘ PANAMA: Chiriqui / P. Nac.Volcan Baru / 5.9km E Cerro Punta , 2150m / 14.Jun.1995 R. Anderson / riparian alder forest litter’ ; 1 spec. ( KSEM): ‘ PANAMÁ: Chiriquí / 5.9 km N Cerro Punta / Par. Nac. Volcan Baru , 2150 m / 8°22′0″N [sic!, = 8°52′0″N], 82°34′0″W / 14 JUN 1995 ; R.Anderson / PAN2A95 22A / ex: alder forest litter’; 1 J, 21 spec. ( ZMUC): ‘ PANAMA: Chiriqui / P. Nac. Volcan Baru / 5.9km E Cerro Punta , 2400m, 14.Jun.1995 R. Anderson / oak ridge-bamboo for. litter’ ; 1 J, 40 spec. ( ZMUC, BMNH, FEFU, NMPC): ‘ PANAMA: Chiriqui / P. Int La Amistad, Las Nubes / 5.3 km W Cerro Punta, 2150m / 15.Jun.1995 R.Anderson / cloud forest litter 95-026 ’; 1J, 3 spec. ( KSEM, NMPC):‘ PANAMÁ: Chiriquí / 6.7 km N Cerro Punta / Par. Nac. La Amistad / Las Nubes , 2150m / 8°22′0″N [sic!, = 8°52′0″N], 82°34′0″W / 15 JUN 1995 ; R.Anderson / PAN2A95 26A / ex: berlese forest litter’; 8 spec. ( ZMUC, NMPC): ‘ PANAMA: Chiriqui, 12 km NE / Santa Clara, Cerro Pando / 2120m, 8°54.74′N 82°43.29′W / 17.Jun.1996 R. Anderson / wet cloud forest litt. 96-134C’ ; 1 spec. ( KSEM): ‘ PANAMA: Chiriquí / 12 km NE Santa Clara / Cerro Pando , 2120m / 8°54′44″N 82°43′30″W / 17 VI 1996 ; R. Anderson / PAN2A96-13C / ex: cloud forest litter’; 1 J, 11 spec. ( ZMUC): ‘ PANAMA: Chiriqui, 12 km NE / Santa Clara, Cerro Pando / 2000 m, 8°54.74′N 82°43.29′W / 17.Jun.1996 R. Anderson / wet cloud forest litt. 96-135C’ ; 1 J, 1 ♀, 4 spec. ( FMNH): ‘ Cerro Punta (on trail to / Boquete) Chiriquí / Prov., PANAMA / alt. 7000 ft // CNHM Panama / Zool. Exped (1959) / March 1 1959 / H. S. Dybas lgt. // Berlese (B-425) / flood debris on / steep wooded slope’ ; 1♀, 1 spec. ( FMNH): ‘ PANAMA: Chiriqui Prov. / ‘ Casita Alta’, Finca / Lerida nr. Boquete / III. 18. 1959, 6900 ft // Berlese (B-543) / conc. floor debris / in damp ravine / leg. / H. S. Dybas’ ; 1 ♀ ( ZMUC): ‘ PANAMA: Chiriqui / 30.7 km W Volcan / Hartmann’s Finca , 1450m / 14. Jun.1995 R.Anderson / wet montane trop. fore. litter’ . COSTA RICA: 4 spec. ( KSEM): ‘ COSTA RICA: Limon / Valle de Silencio, Estación / 82°57′43″W 09°06′37″N / 2473m, 26-27.ii.2005 / R. Anderson, oak forest litter / CRA105 002 ’; 3 JJ, 50 spec. ( INBio, KSEM, NMPC): ‘ COSTA RICA: Limon Prov. / Valle de Silencio, Estacion / 26-27.ii.2005, 2473 m / 82°57′43″W 09°06′37″N / Oak Forest Litter, R. Anderson’ .

Additional material. COSTA RICA: 4 ♀♀ ( KSEM, NMPC): ‘COSTA RICA: Limon Prov. / Valle de Silencio, Estacion / 26-27.ii.2005, 2473 m / 82°57′43″W 09°06′37″N / Oak Forest Litter, R. Anderson’.

Differential diagnosis. Preepisternal plate of mesothorax 1.7× as long as wide ( Fig. 19 ); anterolateral ridges sinuate near lateral margin of metaventrite ( Fig. 19 ); punctation of median portion of metaventrite coarse ( Fig. 19 ); punctation of mentum sparse ( Fig. 17 ); number of spines of inner ventral mesotibial series sexually dimorphic (as in Figs. 12 and 13 ); aedeagus large (0.75–0.80 mm); median lobe bottleneck shaped, strongly constricted subapically; parameres widely rounded apically ( Figs. 7 and 8 ).

Oosternum convexum sp. nov. is easily recognizable from the remaining two species of the group by the distinctly larger and more sclerotized aedeagus with strongly constricted apical portion of the median lobe. Externally it differs from O. simplex sp. nov. and O. intermedium sp. nov. by the characters given in the identification key and usually also by slightly different coloration of elytra, which are often slightly paler, at least on the base of elytral intervals 2 and 4 (elytra of the other two species are uniformly coloured). Specimens with costate elytra (see Variability) are very distinct from O. simplex sp. nov., O. intermedium sp. nov. as well as from typical form of O. convexum sp. nov. and cannot be confused with any other Oosternum species known to us.

Description. Body elongate oval, body length / body width ratio = 1.65. Body length: 1.30–1.80 mm (length of holotype: 1.80 mm); width: 0.80–1.05 mm (width of holotype: 1.05 mm).

Coloration. Dorsal side ( Figs. 1 and 2 ) pale brown, anterior margin of clypeus, lateral margins of pronotum, basal most part of elytral interval 3, humeral area of elytron and lateral elytral margin yellowish brown. Ventral side brown to dark brown, epipleura yellowish brown; femora brown to dark brown basally, yellowish apically; tibiae and tarsi yellowish.

Head. Clypeus with sparse punctation consisting of moderately large punctures; interstices with fine microsculpture. Frons with sparse punctation consisting of large, rounded, uniformly shaped punctures. Eyes separated by 11 widths of one eye. Mentum with sparse punctation ( Fig. 17 ). Submentum with poriferous disc-like areas. Antennal club approximately twice as long as wide.

Prothorax. Punctation of pronotum slightly denser than on head, consisting of rather large, slightly rasp-like punctures. Median carina of prosternum, in lateral view, straight.

Mesothorax. Scutellar shield bearing few minute punctures. Elytral series 1–3 and 5–7 arising basally, series 4, 8 and 9 subbasally; serial punctures fine, rather dense; denticulation of lateral elytral margin distinct throughout elytral length except at apex. Preepisternal plate ( Fig. 19 ) wide, drop-like, 1.7× as long as wide; median part slightly concave, bearing a few large, sparsely distributed setiferous punctures.

Metathorax ( Fig. 19 ). Punctation of median portion of metaventrite coarse and sparse, bearing decumbent setae.Anterolateral ridges angularly bent posteriad laterally. Anepisternum 4.9× as long as wide.

Legs. Inner ventral series of stout spines on metatibiae sexually dimorphic, with more apical spines in male (as in Figs. 12 and 13 ).

Male genitalia ( Figs. 7 and 8 ). Aedeagus 0.75–0.80 mm long. Parameres 0.7× as long as phallobase, slightly narrowing towards blunty rounded apex. Phallobase 2.0× as long as wide. Median lobe slightly widened from base towards apical 0.15, then strongly constricted into a narrow, bottleneck-shaped apex; lateral projections wide but developed only subapically.

Variability. Very variable species, especially in body size and coloration of dorsal surface (elytra uniformly pale brown without any trace of paler coloration to distinctly pale at base of all elytral intervals). Four females (see Additional material) differ by a distinctly elevated elytral interval 3 that becomes slightly keel-like subbasally and replaces elytral interval 2 near the anterior third of the elytron (i.e., interval 2 is developed only basally and apically, Fig. 23 ). These aberrant specimens were collected together with the typical form at the Valle de Silencio ( Costa Rica); no intermediates between typical and keeled forms were found. Detailed examination of the aberrant specimens using SEM showed no difference from typical form in other external characters. We therefore consider that these specimens belong to O. convexum sp. nov. One male from the Valle de Silencio (deposited in NMPC) differs from the remaining examined specimens by narrow apices of parameres bearing a small subapical denticle; since no other differences were found in external characters of this specimen, even using SEM, we also consider that this specimen belongs to O. convexum sp. nov.

Etymology. Referring to the convex body.

Bionomics. All specimens were sifted from leaf litter in oak and oak-bamboo cloud forests and alder riparian forest at altitudes of 1,450 –2,500 m a.s.l.

Distribution ( Fig. 24 ). Known from a cluster of several localities in the southern part of the Cordillera de Talamanca Mts. in Panama and Costa Rica. All localities are situated in the southern part of La Amistad International Park.

Figures

Figs. 1–2. Habitus of Oosternum convexum sp. nov.: 1 – dorsal view, 2 – lateral view. Body length: 1.75 mm.

Figs. 3–8.Aedeagophores.3, 5, 7 – whole aedeagus; 4, 6, 8 – detail of apical portions of parameres and median lobe. 3–4 – Oosternum simplex sp. nov.; 5–6 – O. intermedium sp. nov.; 7–8 – O. convexum sp. nov.

Figs. 9–16. Diagnostic characters of the Oosternum convexum species group. 9 – prosternum; 10 – elytral apex (arrow: elytral interval 2); 11 – detail of basal portion of epipleuron (note marginal denticulation); 12 – ventral surface of mesotibia (female); 13 – ditto male (arrow: multiplied spines in inner row); 14 – detail of elytral surface (arrows: small denticles at each serial puncture); 15 – terminal abdominal sclerites of male (st8: sternite 8; st9: sternite 9; ter8: tergite 8); 16 – head in lateral view. 9, 11, 14 – O. convexum sp. nov.; 10, 12 – O. simplex sp. nov.; 13, 15, 16 – O. intermedium sp. nov.

Figs. 17–23. Differential characters of species of Oosternum convexum group. 17–18 – mentum; 19–21 – meso- and metaventrite (arrow: different shapes of lateral part of anterolateral ridge of metaventrite); 22–23 – right elytron (arrow: elytral interval 3). 18, 20, 22–23 – O. convexum sp. nov.; 19, 22 – O. simplex sp. nov.; 20 – O. intermedium sp. nov.

Fig. 24. Distribution of the Oosternum convexum species group.