Thinophilus tesselatus Becker, 1922

Mukherjee, Koustav, Pramanik, Debdeep, Naskar, Atanu & Banerjee, Dhriti, 2023, A new species of Thinophilus Wahlberg (Diptera: Dolichopodidae: Hydrophorinae) from coastal India with re-description of Thinophilus tesselatus Becker (Diptera: Dolichopodidae: Hydrophorinae), Zootaxa 5375 (4), pp. 478-494 : 486-491

Thinophilus tesselatus Becker

( Figs 14–17 )

Thinophilus tesselatus Becker, 1922: 35 .

Type material examined. SYNTYPE: 1 ♂ ( Fig. 17 ) labelled: “tesselatus / Beck.”; “Rajshai/ E. Bengal/ 1- 6 II. 7” ( ZSI) .

Additional material examined. INDIA. West Bengal: 1 ♂ ZSI 25373/H6 , Sagar Island, Bay of Bengal , 21°51′43.78″ N, 88°7′46.16″ E, alt 0m, coll. K. Mukherjee, sweep netting, 18 Feb. 2021 ; 1 ♂ ZSI 25372/H6 , Maheshtala, Kolkata , 22°29′45.69″ N, 88°16′13.32″ E, alt 3 m, coll. K. Mukherjee, sweep netting, Nov. 2021 ; 1 ♀, Calcutta , T. tesselatus [det. Becker].

Diagnosis. A large species; scape brown with a hook-like flap; pedicel and roundish postpedicel dorsally brown, ventrally yellow; arista dark brown and bare. 8–9 dorsocentral bristles all uniformly small except the posterior most. A median longitudinal stripe present on scutum. All coxae black with yellow apex; lateral setae present on hind coxa. Fore tibia with two rows of uniformly long ventral hairs and two pairs of preapical bristle; mid and hind tibiae lack the long ventral bristle of fore tibia. Laterally, first five abdominal segments display prominent square azure blue coloration; sixth abdominal tergite fully azure blue.

Redescription. Male ( Fig. 14 ). Body length: 7.5 mm, wing length: 5.6 mm. Head ( Fig. 15 ): Dichoptic reddish-brown eyes with white pubescence; vertex metallic green; pair of outer vertical setae, pair of inner vertical setae, pair of ocellar setae, 9–10 postocular setae, interfrontal and fronto-orbital setae absent; postgenal region with dense white long hairs; yellow palpus with black setae; frons and clypeus metallic green with minute hairs; brilliant violet triangular patch just below median ocellus. Antenna with arista bare, dark brown; scape with hook-like flap, pedicel and postpedicel dark brown dorsally and yellowish-orange ventrally; roundish postpedicel. Proboscis and palpus dark brown; length ratio of scape to pedicel to postpedicel to arista,0.07/0.08/0.18/0.86. Thorax: Median brownish longitudinal stripe with multi-colored reflections; scutellum metallic green, with 2 strong longer marginals and 2 shorter hair-like laterals; anterior and posterior spiracles yellow without external hairs; acrostichal setae absent; 8–9 dorsocentral bristles, posterior most dorsocentral bristle largest, remaining uniformly small; 1 postalar bristle, 1 notopleural bristle, 1 humeral bristle, with pair of postpronotal bristles, one longer than other; halter yellow; calypter with tufts of while pale yellow hairs. Wing: Light grey; vein M 1 with dip slightly distant from dm-m crossvein, M 4 and dm-m nearly equal in length. Leg: All coxae black with yellowish apical end, with strong seta on each; trochanter yellowish. Fore leg: Femur half dark brown and half yellowish ventrally; dorsally reddish-brown and darker towards apical end; femur with multiple rows of bristles increasing in length apically; tibia with reddish-brown longitudinal stripe along upper margin, remaining blackish; short black bristles throughout tibia with two rows of uniform long hairs ventrally and 3 pairs of longer bristles dorsally; two pairs of preapical bristles; basitarsus dark brown with uniform rows of teeth-like bristles along with long hairs in between; all tarsal segments black; length of femur, tibia and tarsomeres (in mm): 1.68/1.28/0.43/0.21/0.19/0.18/0.18. Mid leg: Femur reddish-brown, not as dark as fore femur, short black setae throughout, slightly larger apically; multiple rows of black setae throughout tibia, without two rows of uniform long ventral hairs, 3 pairs of long, strong dorsal bristles; 4 strong preapical tibial bristles; basitarsus and tarsomeres lighter compared to foreleg; spur at apical end of all tarsomeres except tarsomere 5; length of femur, tibia and tarsomeres (in mm): 1.49/1.66/1.10/0.28/0.18/0.13/0.15. Hind leg: Femur coloration is lighter compared to fore and mid femora, basal three-fourth yellowish dorsally, brownish ventrally, remaining blackish, apex yellow; tibia, basitarsus and tarsomeres as in midleg, except presence of 6–7 longer bristles on hind tibia; length of femur, tibia and tarsomeres (in mm): 2.43/2.53/0.66/0.48/0.29/0.25/0.19. Abdomen: Ground color varying from yellowish-grey to greenish; tergites 1–5 dorsally appears metallic green with dark triangular patches along midline; tergite 6 wholly azure metallic blue; tergites 1–5 laterally with prominent square azure blue coloration; sternites and tergites similar in color; sternites with patches of white soft hairs, tergites covered with uniform small black setae. Male genitalia ( Fig.16 ): Male terminalia exposed outside body; epandrium black; cerci long, fused medially with rows of long black bristles ventrally and tuft of black bristle at apex; surstylus shiny black with rows of black bristles along margin; phallus thin and coiled. Female. Similar to male except lacking male secondary sexual characters (MSSC).

Distribution. India (West Bengal), Bangladesh (Rajshahi), Taiwan (Tainan), Thailand (Chonburi, Rayong), Philippines (Mindoro).

Remarks. Thinophilus tesselatus was collected from two localities: a freshwater pond from Sagar Island and a mud puddle in Maheshtala, Kolkata, thereby confirming its status as a freshwater species. It was first described by Becker (1922) from Tainan city (Taiwan), and Rajshahi ( Bangladesh), the male syntype and other specimens identified by Becker are deposited in the NZC of ZSI, where we borrowed the male syntype for reference ( Fig. 17 ). The original description by Becker is accurate except it lacked the detailed description of the species. This work provides a complete description of the male with morphometrics and photographs. Furthermore, for almost after a century we found the species from the same zone indicating the resilience of the species even after the drastic changes in natural habitat and topography of the region that have occurred.

Figures

FIGURE 14. Thinophilus tesselatus Becker, 1922, ♂, lateral habitus.

FIGURE 15. Thinophilus tesselatus Becker, 1922, ♂, head A. Frontal view; B. Lateral view.

FIGURE 16. Thinophilus tesselatus Becker, 1922, ♂, Male terminalia A. Lateral view; B. Dorsal view. Abbreviations: Cerc: Cerci, Ph: Phallus, Sur: Surstylus.

FIGURE 17. Thinophilus tesselatus Becker, 1922, ♂ syntype.