Hercostomus obtusus Samoh & Grootaert 2024, sp. nov.

Hercostomus obtusus sp. nov.

(Figs 1–3)

Type material. HOLOTYPE ♂, THAILAND: Phang Nga province, Thai Mueang district, Thai Mueang subdistrict, Ban Thap Pla, Mangrove creek and local fishing port (8°28’58.6»N, 98°15’17.5»E), sweep netting, 4.IV.2021, A. Samoh leg., PSUNHM, PSUZCEN10. PARATYPES. THAILAND: Satun province, 3 ♂, 2 ♀, Langu district, Langu subdistrict, Pakbara (6°50’30.4”N 99°46’32.9”E), sweep netting, 29.IV.2015, A. Samoh leg., PSUNHM. SINGAPORE: 4 ♂, 1 ♀, Semakau 3. V.2012 (Ma 0111); 2 ♂, Pulau Ubin (PU2), 23.III.2016 (Ma 9322); 1 ♀, Sungei Buloh (SB2), 30.X.2013 (Ma 8598); leg. P. Grootaert); 1 ♂, Pulau Tekong PT1 (ZRCBDP00001445, barcoded) LKCNHM, Singapore.

Other material examined: SINGAPORE: A total of 636 specimens from Singapore consisting of 381 males and 255 females were examined, 182 specimens were NGS-barcoded and deposited at LKCNHM, Singapore with some vouchers at RBINS.

Diagnosis. First flagellomere with a blunt, rounded apex, elongate, in male 2.3 times as long as wide (Fig. 1); in female 1.5 times as long as wide (Fig. 2). Legs yellow, except mid and hind coxae brownish (Figs 1, 2). Hind femur lacking ventral bristling. Male genitalia (Fig. 1) long, about 3/4 as long as abdomen length. Epandrium brown, appendages yellow, cerci white with fine white bristling.

Description. Male (Fig. 1). Small species (body length 3.8–4.0 mm, wing length 3.1–3.3 mm). Head metallic green with pale grey pollen. Face almost parallel sided, wide, slightly wider than width of first flagellomere, weakly narrowing downward. All hairs and bristles black, including uniserial postocular bristles (not much longer below than above).Antenna (Fig. 1) blackish brown; first flagellomere elongated, oblong-shaped, 2.3 times as long as wide; arista dorsal, inserted near base of first flagellomere. Proboscis blackish brown with pale hairs, palpus yellowish with pale hairs, lacking strong bristles. Thorax metallic green with pale grey pollen. Hairs and bristles black. Six strong dc, gradually becoming longer toward scutellum, 6 pairs of acr; scutellum with 2 pairs of bristles: pair of very long bristles, widely separated, inserted on lateral tip of scutellum and shorter fine pair outside. Propleurals above, minute, whitish, below with 1 long black bristle. Legs yellow, including fore coxa; mid and hind coxae brown. Hairs and bristles black. Fore coxa with short black anterior bristles and 3 very long apical bristles. Mid and hind coxae each with 1 exterior bristle. Mid trochanter with very long black apical bristle. All femora lacking ventral bristling. Mid and hind femora each with 1 long black preapical bristle. Fore tibia with 1 ad bristle at basal third twice as long as tibia, 1 dorsal near middle and 1 preapical dorsal. Mid tibia with 3 ad, 2 pd and 1 av, apically with 4 bristles; hind tibia with 3 ad, 3 pd and 1 shorter av, apically with 3 bristles. Wing hyaline, brownish tinged; veins brown, R 4+5 and M 1+2 parallel apically. Squama whitish with long black hairs. Halter with white knob, but dusky stem. Abdomen metallic green with pale grey pollen. Hairs and bristles black. Male genitalia long, about 3/4 as long as abdomen (Fig. 1). Epandrium brown, appendages yellow, cerci white with fine white bristling. Epandrium slightly more than 2x as long as wide. Apicoventral epandrial lobe yellow, with rounded apex and set with 3 bristles (a long preapical and two shorter apicals. Basoventral epandrial lobe brown, with truncate tip and minute hair anteriad. Hypandrium pale with somewhat acute apex. Aedeagus long and fine, with row of minute spinules on apical quarter (Fig. 3A inset). Ventral surstylus elongate with narrow dorsal lobe bearing strong apical bristle (Fig. 3B). Dorsal surstylus with subapical bristle (Fig. 3B). Cercus small, set with only fine yellowish white bristles and microtrichia. Tip of cercus apically somewhat triangular with ventral side rounded in lateral view (Fig. 3C) with long basal lobe covering tip of epandrium (Fig. 3C, D).

Female (Fig. 2). Body length 2.5–2.6 mm, wing length 2.1–2.2 mm. Similar to male, except first flagellomere about 1.5 times as long as wide.

Etymology. The specific epithet, obtusus refers to the obtuse tip of the first flagellomere.

Bionomics. This species was collected from shaded areas of the back mangrove.

Distribution. THAILAND: Phang Nga and Satun provinces (Andaman Seacoasts, southern Thailand) (Fig. 7). SINGAPORE: common in the back mangrove all over the country.

Remarks. The new species is the only mangrove species with a long first flagellomere with an obtuse, rounded apex, while all the other species have an acute tip. The genetic distance between the population of H. obtusus sp. nov. between South-Thailand and Singapore is between about 3 %, but no morphological differences have been identified.