Hydraena (Hydraenopsis) palawanensis Freitag & Jäch, sp. n. (Figs. 10, 22a–h) Type locality. Residual river pools, Mate, Municipality of Brooke’s Point, 08°46'N 117°50'E, southern Palawan, Philippines. Type material. Holotype ɗ (NMW): “ PHIL.: Palawan Brooke’s Point Mate, 31.3.1994 leg. Zettel (54)”, terminal parts of abdomen and aedeagus glued separately. Paratypes: 44 ɗɗ (37 exs. NMW, 3 exs. mutilated; 2 exs. IRML; 2 ex. UPLB; 2 ex. WPU; 1 ex. CZW), 23 ΨΨ (21 exs. NMW; 1ex. UPLB; 1 ex. WPU): same locality data as holotype; 13 ɗɗ (NMW, 2 exs. mutilated, aedeagus of 1 ex. lacking), 9 ΨΨ (NMW, 1 ex. mutilated): “ 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”; 6 ɗɗ (NMW; 1 ex. IRML), 5 ΨΨ (NMW): “ PHIL.: Palawan, P.Princesa; S. Vincente Taranaban Riv; 0.5km N of Highway, mountain riv. resid. pool, 10m asl 10°01'N 119°01'E, 30.4.1995 leg. Freitag (16)M”; 1 ɗ (NMW): “ PHIL.: Palawan, P.Princesa; Luzvimin-da,Villa Bukit, garden/farmland creek 8km SSW PPC; 20m asl 9°40'N 118°43'E, 25.3.1995 leg. Freitag(21)M”; 1 ɗ (NMW): “ PHIL.: Palawan, P.Princesa; Luzviminda, forest creek, small fall, 9km SSW PPC; sandy banks, pool, c. 50m asl 9°39'N 118°38'E, 14.12.1994,leg.Freitag(17b)M”; 1 ɗ (NMW): “ PHIL.: Palawan, P.Princesa; Luzviminda, forest creek, small fall, 9km SSW PPC; side pools w/ leaves, c. 50m asl 9°39'N 18°38'E, 14.12.1994,leg.Freitag(17c)M”; 2 ɗɗ (NMW, 1 ex. mutilated): “ PHIL.: Palawan, P. Princesa SE Manturon, Cabayugan R. 10°09.486'N 118°53.493' E 3.3.2001, leg. Freitag (i4)”; 1 ɗ (NMW): “ PHIL.: Palawan, P. Princesa S Manturon, Cabayugan R. 10°09.259'N 118°52.503' E 31.7.2001, leg. Freitag (i3)”; 1 ɗ (NMW): “ PHIL.: Palawan, P. Princesa SE Manturon, Karst spring LS4R 10°09'29''N 118°53'30''E 21.IV.2001, leg. Freitag (i34) E”; 1 ɗ (NMW): “ PHIL.: Palawan, P. Princesa SE Manturon, Karst spring LS4R 10°09'29''N 118°53'30''E; 21.IV.2001, leg. Freitag (i35) E”; 1 ɗ (NMW): “ PHIL.: Palawan, P. Princesa SE Manturon, Karst spring LS4R 10°09'29''N 118°53'30''E 18.III.2001, leg. Freitag (i51) E”; 1 ɗ (NMW): “ PHIL.: Palawan, P. Princesa SE Manturon, Karst spring LS4R 10°09'29''N 118°53'30''E 18.III.2001, leg. Freitag (i52) E”; 1 ɗ (WPU): “ PHIL.: Palawan, P. Princesa Cabayugan R.; Nagdayan Creek, Manturon Bridge 10°10'N 118°53' E 27.3.2001, leg. Freitag (5)M”; 1 ɗ (UPLB): “ PHIL.: Palawan, P. Princesa Cabayugan R.; Nagdayan Creek, Manturon Bridge 10°10'N 118°53' E 27.3.2001, leg. Freitag (2)M”; 1 ɗ (NMW, mutilated): “ PHIL.: Palawan, P. Princesa Cabayugan R.; Nagdayan Creek, Manturon Bridge 10°10'N 118°53' E 27.3.2001, leg. Freitag (3)M”; 1 ɗ (NMW, mutilated): “ PHIL.: Palawan, P. Princesa S Manturon, Cabayugan R.CR4 10°09'28''N 118°53'26''E 18.III.2001, leg. Freitag (i41)E”; 1 ɗ (NMW), 5 ΨΨ (NMW, 1 ex. mutilated): “ PHILIPPINES Sabang, N. of Mt. St. Paul, Palawan July, 11–13, 1977 M. Satô leg.”. Description. Body 1.10–1.25 mm long. Habitus as in Fig. 10. Elytra brown; rectangular spot in the middle of pronotal disc and frons (particularly around eyes) darker brown; pronotal margins, legs, maxillary palpi and sometimes posterior third of elytra distinctly paler. Pronotum wider than long, broadest at the middle; entire pronotum moderately densely punctate, sometimes appearing bristled; punctures very small and shallowly impressed, interstices glabrous; foveae slightly impressed or inconspicuous; anterior margin slightly concave; anterior angles rounded; lateral rim inconspicuously denticulate; lateral margins anteriorly convergent, posteriorly sinuously convergent; pronoto-elytral angle obtuse; posterior margin slightly biconcave; lateral hypomeron posteriorly slightly broader than profemur; mesal hypomeron narrow, inconspicuous. Elytra elongately oval, usually not conjointly rounded apically, with inconspicuously small acute notch, with ca. 14 longitudinal, more or less regular, inconspicuous rows of punctures (approximately eight between suture and shoulder); punctures very small and very shallowly impressed; interstices and intervals almost flat, almost glabrous; lateral portion narrow, reaching ca. posterior 0.3; inflexed lateral portion moderately wide (ca. as broad as metafemur), very short (reaching ca. posterior 0.3); pseudepipleuron without conspicuous row of punctures. Mesoventrite very deeply impressed, with well developed longitudinal ridges; mesoventral intercoxal process very wide and long, broader than pseudepipleuron, reaching beyond posterior margin of mesocoxa, firmly connected with metaventrite. Metaventral disc slightly impressed; metaventral plaques moderately widely separated (as wide as inflexed lateral portion of elytron), slightly convergent anteriorly, moderately narrow, glabrous; intercoxal sternite moderately large, approximately as broad as metafemur; metaventrite and abdominal sternites moderately pubescent. Femora almost as in Hydraena nielshaggei. Protibiae slightly bent. Aedeagus (Figs. 22 a–c) basally slender, strongly widening in apical 0.7 (dorsal/ventral view). Main piece without setae (five micropores present), right margin with distinct emargination near insertion of right paramere, apex sinuous and slender; phallobase almost symmetric. Distal lobe intricately shaped, ventrally with strongly sclerotized, bisinuous structure, medioapically with tapered appendix. Parameres articulately connected with main piece; left paramere very small, inserted ventro-lateral, at about basal 0.2 of aedeagus, apically with five short setae; right paramere distinctly longer and broader, inserted at about basal 0.25 of aedeagus, less sclerotized, with inconspicuous tiny apical bristles and with irregular ventro-median longitudinal row of ca. six moderately long setae. Gonocoxite (Fig. 22 e) subtriangular; apical area of ventral plate very short; margin between apical and basal area not clearly defined; setae of subapical tufts almost straight; basal area of ventral plate sparsely setose apically; condyles moderately large, distinctly retracted; dorsal plate not surpassing outer plate, with one moderately large cavity. Spermatheca (Figs. 8f–g). Proximal portion crescentic, with a pair of tiny appendages; distal portion more or less discoidal. Secondary sexual characters. Basoventral corner of male femur more acute than in female (dissection of leg recommended). Male terminal sternite pyriform (Fig. 22 d). Male tergite X distinctly excised apically. Female tergite X (Fig. 22 h) subsemicircular; disc moderately densely setose; subapical fringe setae trichoid, not arranged in regular row; hyaline apical margin with three notches. Differential diagnosis. The external habitus of this species is similar to Hydraena nielshaggei and H. jojoorculloi, from which it can be distinguished externally by the subquadrate pronotum with inconspicuous lateral denticulation, the small and shallowly impressed elytral and pronotal punctures, the bent protibiae, and unusual mesoventral process. Furthermore, its male genital characters (aedeagus strongly widened apically, distal lobe intricately shaped, distinctly unequal parameres articulately connected to main piece) allow to distinguish it from all other species. Distribution (Fig. 31). Hydraena palawanensis was so far collected in central and in southern Palawan. Ecology. This species is encountered in undisturbed pristine forests (e.g. LS4) and in moderately disturbed rural areas (CR3; Freitag 2005), which suggests a rather high ecological potency. Most specimens of Hydraena palawanensis were collected in residual pools of a small stream, and between CPOM in sandy slack-water zones of small lowland streams. Additional material was retrieved from emergence traps positioned over pool sections of first to fourth order streams. Therefore it is likely that the species inhabits the detritus intersticial and avoids strong currents. Etymology. This species is named after Palawan, in reference to its comparably wide distribution on this island.

Published as part of 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, pp. 1-44 in Zootaxa 1431 on pages 26-29, DOI: 10.5281/zenodo.175790