Hydraena (Hydraenopsis) castanescens Freitag & Jäch, 2007

Freitag, Hendrik & Jäch, Manfred A., 2007, Revision of the species of Hydraena Kugelann (Coleoptera: Hydraenidae) from Palawan and Busuanga, with descriptions of eleven new species, and redescription of Hydraena (Hydraenopsis) scabra d’Orchymont, 1925, Zootaxa 1431, pp. 1-44 : 19-22

Hydraena (Hydraenopsis) castanescens Freitag & Jäch , sp. n.

(Figs. 7, 19a–h)

Type locality. Alipuran Stream (Lake Manguao tributary), Municipality of Taytay, northern Palawan, Philippines.

Type material. Holotype ɗ ( NMW): “ PHIL.: Palawan, Taytay; Lake Manguao tributary, Alipuran Stream, semi-prim. forest c. 40m asl, 10°45'N 119°32' E 29.4.1995, leg. Freitag (15)M”, terminal parts of abdomen and aedeagus glued separately, one mesotibia and mesotarsus and one metatarsus lacking.

Additional material. 1 Ψ ( NMW) “ PHIL.: Palawan, P. Princesa, Sabang, Mt. Bloomfield Waterfall, c. 150m asl 10°12'N 118°53' E 22.12.2000, leg. Freitag (18)M”. This single female was collected about 100 km SSW from the type locality of Hydraena castanescens . Although it is most likely that it represents the female of H. castanescens , we refrain from including it in the type series.

Description. Body approximately 1.4 mm long. Habitus as in Fig. 7. Elytra and rectangular spot in the middle of pronotal disc and frons dark chestnut; pronotal margins, legs and posterior third of elytra pale chestnut; maxillary palpi gold-brown.

Pronotum wider than long, broadest at about anterior 0.35; entire pronotum moderately densely punctate, punctures moderately large and moderately deeply impressed, interstices glabrous; foveae impressed; lateral margins anteriorly slightly and posteriorly distinctly convergent; anterior angles rounded, posterior angles obtuse; pronoto-elytral angle obtuse; lateral rim distinctly denticulate; anterior margin concave, posterior margin very slightly convex, distinctly smaller than elytral shoulder; lateral portions of pronotum anteriorly slightly deflexed; lateral hypomeron slightly broader than profemur, inner margin almost straight; mesal hypomeron very narrow, inconspicuous.

Elytra elongately oval, apically almost conjointly rounded, with ca. 14 longitudinal, more or less regular, not impressed rows of punctures (nine between suture and shoulder); punctures moderately large and moderately impressed; interstices and intervals flat to convex, glabrous; lateral margins of elytra widely explanate, almost reaching elytral apex, not or imperceptibly denticulate; inflexed lateral portion (pseudepipleuron) approximately as broad as metafemur; almost reaching elytral apex (ca. posterior 0.1); epipleuron narrow, inconspicuous.

Mesoventral longitudinal ridges hardly perceptible or absent; meso- and metaventrite pubescent; mesoventral intercoxal process very narrow (about one third of width of pseudepipleuron), truncate, moderately long; metaventral disc distinctly impressed; metaventral plaques almost as broad as disc; intercoxal sternite large, approximately as wide and as broad as metafemur; metaventrite and ventrites pubescent.

Femora with straight inner margins, outer margins conspicuously convex.

Aedeagus ( Figs. 19 a–c) superficially similar to that of Hydraena zetteli , main piece moderately slender, without setae (several micropores present); phallobase subsymmetric. Distal lobe not clearly delimited from main piece; ejaculatory duct distally ending in a tube-like process, which is dorsally embedded in a less sclerotized structure with apical projection. Parameres small, not articulately connected with main piece; left paramere short, inserted at about basal 0.40 of aedeagus, with a longitudinal ventro-mesal fringe of long setae and ca. six moderately long apical setae; right paramere shorter, apically rounded, inserted at ca. basal 0.55 of aedeagus, with a subapical tuft of ca. ten long ventral setae.

Gonocoxite ( Fig. 19 e) subsemicircular, almost as in Hydraena zetteli , but with two separate, rather inconspicuous cavities of dorsal plate.

Spermatheca as in Figs. 19 f–g.

Secondary sexual characters. Male profemur with small denticle near base of ventral face. Metatibiae in male curved, in female almost straight. Male terminal sternite subsymmetrically pyriform to elongately subheptagonal, with slightly emarginate apical margin, firmly connected with moderately long, distinctly curved spiculum gastrale ( Fig. 19 d). Male tergite X slightly excised apically. Female tergite X ( Fig. 19 h): disc moderately densely covered with long trichoid setae; setae of subapical fringe trichoid, medially moderately long; laterally with few long setae; hyaline apical margin notched apically.

Differential diagnosis. Due to size and general habitus Hydraena castanescens appears to be most closely related to H. zetteli , from which it can easily be distinguished by its colour pattern (elytra and rectangular spot in the middle of pronotal disc and frons dark chestnut, other parts paler chestnut), the curved metatibia in male, and its stout aedeagus (with apical notch and short parameral setae).

Distribution ( Fig. 30 ). This species is surely known from the headwaters of Alipuran Stream, a tributary of Lake Manguao , Municipality of Taytay, northern Palawan and known from a waterfall on Mt. Bloomfield at the St. Paul Subterranean River National Park, Sabang, Puerto Princesa City, central Palawan.

Ecology. The holotype of Hydraena castanescens was collected from submerged gravel sediments in a rather undisturbed lentic zone at the bank of a headwater stream surrounded by forest. The female of the species was collected in a small rocky pool beside a temporarily drained water fall.

Etymology. Castaneus (Latin), chestnut coloured. In reference to the prevailing colouration.

Figures

FIGURE 19. Hydraena castanescens sp. n. a – c) aedeagus (holotype) in ventral, dorsal (ventral setae of left paramere omitted) and lateral view; d) male sternite X and spiculum; e) gonocoxite; f – g) spermatheca; h) female tergite X.

FIGURE 30. Collecting sites and geographical distribution of Hydraena species in Palawan and Busuanga, including enlarged map of St. Paul National Park: Hydraena scabra d’Orchymont, H. jojoorculloi sp. n., H. nielshaggei sp. n., H. zetteli sp. n., H. castanescens sp. n., H. claudia sp. n., H. kodadai sp. n.