Neothalassius, Brooks, Scott E. & Cumming, Jeffrey M., 2016

Brooks, Scott E. & Cumming, Jeffrey M., 2016, Neothalassius, a new genus of Parathalassiinae (Diptera: Dolichopodidae s. lat.) from the Pacific coast of South America, Zootaxa 4066 (3), pp. 311-322 : 312-313

Genus Neothalassius gen. nov.

Type-species: Neothalassius triton sp. nov.

Diagnosis. Adults of Neothalassius are easily distinguished from other parathalassiine genera by the head with well-developed parafacial plate; gena distinctly projected below eye ( Figs 9–12 ); mouthparts directed posteriorly with narrow labellum and broad flat palpus ( Figs 3 , 5 , 9–12 ); wing veins M2, dm-m and cell dm absent (Fig. 13); fore coxa spinose ( Fig. 5 ); tarsomere 5 of all legs with dorso-medial projection ( Fig. 4 ); and abdominal sternite 1 with medial projection on the anterior margin ( Fig. 7 ).

Description. Small dark grey flies (body length: 1.2–2.0 mm, wing length: 1.5–1.9 mm), with reduced chaetotaxy ( Figs 3 , 5, 6 ). Male. Head ( Figs 9–12 ): Broader than thorax in dorsal view; rounded or ovoid in lateral view. Compound eye with posteroventral margin concave. Neck inserted high on head. Ocellar triangle conspicuous. Occiput flat or concave on upper median part. Dichoptic, eyes entirely covered with uniform ommatrichia, medial edge with emargination near antenna. Frons broader than high, widening towards vertex. Face widening below with well-developed facial ridge and parafacial plate laterally flanking clypeus. Clypeus not separated from face, higher than wide, deflected posteriorly, largely hidden by flanking parafacial plates. Gena wide, distinctly projected below eye ( Figs 9–12 ). Bristles of head well-differentiated: pair of fronto-orbitals close to base of antennae, pair of anterior ocellars, 1–2 pairs tiny posterior ocellars, pair of postocellars, pair of verticals, upper postocular setae in row, becoming field of setae ventrally across broad postgena. Antenna inserted above middle of head in profile; scape short, funnel-shaped; pedicel spheroidal, with subapical circlet of setulae; postpedicel about 2X longer than wide, drop- or bulb-shaped, clothed in fine hairs; stylus arista-like. Mouthparts ( Figs 3 , 5 , 9–12 ) directed posteriorly with narrow labellum; palpus broad, flat, subrectangular, sensory pit indiscernible; epipharyngeal carina present; epipharyngeal blades narrow; labellum with pseudotracheae indistinct. Thorax: Mesoscutum moderately arched ( Figs 3 , 5 ), prescutellar depression present ( Fig. 6 ). Prosternum fused with proepisternum forming precoxal bridge. Postpronotal lobe distinct with a few small setulae. Mesonotum shield-shaped in dorsal view, slightly longer than wide, bristles well-differentiated. Acrostichal setae absent; 3–4 dorsocentral bristles with weak accessory setae between bristles, 0–1 presutural supra-alar bristle, 1 postsutural supra-alar bristle, 2 notopleural bristles, and 1 post-alar bristle, per side; scutellum broadly subtriangular with 1 pair of erect inclinate bristles near apex. Mesopleuron bare. Wing (Fig. 13): Pterostigma absent, membrane somewhat translucent, entirely covered with minute microtrichia, anal lobe not developed, alula absent. Costa (C) circumambient, with strong bristle at extreme anterior base. Anterior costal section bearing row of short spine-like setae intermixed with fine setae from Sc to R2+3, posterior part of costa beyond R2+3 with only fine setae. All longitudinal veins complete, reaching wing margin, Sc faint apically. R1 straight. R2+3 diverging from R4+ 5 in basal half, gradually curved posteriorly to run parallel to R4+ 5 in distal half. R4+5 straight. M1 diverging from R4+ 5 in basal half, gradually curved anteriorly to run subparallel to R4+ 5 in distal half. M2 absent. M4 mainly straight with slight posterior curve apically. Base of Rs originating opposite humeral crossvein. Crossvein r-m short, trace-like or indiscernible. Crossvein bm-m appearing incomplete, depigmented at junction point with M1. Crossvein dm-m and cell dm absent. Cells bm and cua in basal fourth of wing, subequal in length and width. Cell cua closed with distal end rounded. Vein CuA+CuP short. Calypter with fine setae. Legs: Almost entirely devoid of well-developed bristles, mostly clothed with fine pale setae; tarsal claws, pulvilli and empodium normally developed on all legs; tarsomere 5 of fore, mid and hind legs with dorso-medial projection ( Fig. 4 ). Foreleg: Coxa with field of short, stout, spine-like setae on anterior surface ( Fig. 5 ); tibia with apical comb-like row of closely-spaced setae medially; tarsomere 1 modified, with slight ventromedial excavation or large basiventral swelling; tarsomeres 2 and 3 with row of minute spine-like setae ventrally. Midleg: Coxa with a few weak setae on anterior surface; tibia with apicoventral bristle; tarsomeres 1–4 with stronger setae on apicoventral margin. Hindleg: Coxa with a few fine setae on outer surface; tibia with apical comb-like row of closely-spaced setae medially adjacent apicoventral bristle; tarsomeres 1–4 with somewhat stronger setae on apicoventral margin. Abdomen (see Figs 3 , 6, 7, 8 ): Abdominal muscle plaques present. Tergites 1–6 and sternites 1–5 sparsely clothed with short, fine setae; sternite 6 and 7 bare; tergite 7 with 1 small posterolateral seta per side, otherwise bare. Sternite 1 with medial spine-like or nipple-like process on anterior margin ( Fig. 7 ). Segments 1–4 symmetrical with simple subrectangular tergites and sternites; segments 5–7 narrowed, somewhat more heavily sclerotized (especially segments 6 and 7) and laterally compressed to form cavity on right side for hypopygium. Sternite 5 with broad projecting pregenitalic process with membraneous apex. Sternite 8 more or less subquadrate, forming dome-like cap over anterodorsal region of hypopygium; tergite 8 reduced to narrow band-like sclerite. Hypopygium ( Figs 16–21 ): Lateroflexed to right; inverted with posterior end directed anteriorly; compact, less than half length of abdomen; asymmetrical; foramen not formed. Epandrium divided into left and right lamellae. Left epandrial lamella ( Figs 16 , 19 ) partially overlapping left side of hypandrium, posterior margin trifurcate, ventral margin broadly rounded and fused with hypandrium but epandrial margin distinct; ventral epandrial process present, elongate with rounded apex, apparently not articulated at base. Left surstylus bilobed, dorsal and ventral lobes separated by deep U-shaped cleft through which left postgonite lobe protrudes. Dorsal lobe of left surstylus with large curved apical bristle and weaker dorsal seta, ventrally with short tubercle bearing thick spatulate apical seta (prensiseta). Ventral lobe of left surstylus with 1 ventral seta and pair of closely-set thickened setae (prensisetae) on medial surface. Right epandrial lamella ( Figs 17 , 20 ) partially overlapping right side of hypandrium, subtriangular, fused with hypandrium along lower margin, ventral epandrial process present. Right surstylus bilobed, dorsal and ventral lobes separated by deep U-shaped cleft through which right postgonite lobe protrudes. Dorsal lobe of right surstylus with large curved apical bristle and weaker dorsal seta, with thick seta (prensiseta) on medial surface. Ventral lobe of right surstylus bifurcate with elongate dorsal portion lying behind postgonite lobe, bearing 2 ventral setae; ventral portion tapering distally with apical seta. Hypandrium reniform or elongate-reniform in lateral view. Postgonite with basal internal portion cradling base of phallus and ejaculatory apodeme, left and right postgonite lobes large and globular, protruding out from between dorsal and ventral lobes of surstylus. Phallus tubular, J-shaped, bent upwards. Ejaculatory apodeme keel-like, laterally flattened. Hypoproct projected as a pair of sac-like, mainly membraneous asymmetrical lobes. Cercus small with setose dorsomedial lobe and lateral tubercle (joined with hypoproct) bearing apical seta ( Figs 18 , 21 ). Female (not known for N. villosus sp. nov.): Similar to male except: legs with fore tarsomere 1 unmodified; abdominal sternite 1 with smaller medial process on anterior margin; apical abdominal segments retracted into segment 5 (segments 6–8 glabrous); terminalia (Figs 14, 15) with tergite 8 medially divided, narrowly fused with sternite 8 anterolaterally; tergite 10 medially divided with three acanthophorite spines on each side; cercus heavily sclerotized, narrow, pointed apically; spermatheca apparently an unsclerotized unpigmented tube with sperm pump at base.

Etymology. The generic name is derived from neo for new, in reference to the New World Neotropical distribution of the genus and thalassius, a common parathalassiine suffix for sea coast. The gender is masculine.

Distribution and habitat. Neothalassius gen. nov. is found on rocky seacoasts of Chile ( Figs 1, 2 ) and is currently known to range from Cuya in the northern Tarapacá Region (Region I), south to Chiloé Island (i.e., Chepu) in the Los Lagos Region (Region X) ( Figs 22, 23 ).

Figures

FIGURES 9 – 12. Heads of males. 9. Neothalassius triton sp. nov., anterior view. 10. Neothalassius triton sp. nov., lateral view. 11. Neothalassius villosus sp. nov., anterior view. 12. Neothalassius villosus sp. nov., lateral view. Abbreviations: ar stylarista-like stylus; gn—gena; lbl—labellum; pafc—parafacial; plp—palpus; pped—postpedicel.

FIGURES 1 – 4. Neothalassius gen. nov., habitat photographs, male habitus and hindleg. 1 – 2. Rocky coastal site at Algarrobo, Chile, with Santiago dipterist Christian Gonzalez in foreground at left (photographs by Steve Marshall). 3. Neothalassius triton sp. nov., lateral habitus of holotype ♂. 4. Neothalassius triton sp. nov., male hindleg, apex of tibia and tarsus, dorsal view. Abbreviation: tsm—tarsomere.

FIGURES 5 – 8. Neothalassius villosus sp. nov., male habitus and abdomen. 5. Lateral habitus of holotype ♂ (antennal aristalike stylus broken off). 6. Dorsal habitus of holotype ♂ (antennal arista-like stylus broken off). 7. Male abdominal sternites of paratype ♂. 8. Postabdomen of holotype ♂, dorsal view. Abbreviations: proc—process; st—sternite; tg—tergite.

FIGURES 16 – 18. Neothalassius triton sp. nov., male terminalia. 16. Hypopygium, left lateral view. 17. Hypopygium, right lateral view. 18. Proctiger, dorsal view. Abbreviations: cerc—cercus; d sur—dorsal lobe of surstylus; ej apod—ejaculatory apodeme; epand—epandrium; hypd—hypandrium; hyprct—hypoproct; pgt—postgonite; pgt lb—postgonite lobe; ph—phallus; v epand proc—ventral epandrial process; v sur—ventral lobe of surstylus.

FIGURES 19 – 21. Neothalassius villosus sp. nov., male terminalia. 19. Hypopygium, left lateral view. 20. Hypopygium, right lateral view. 21. Proctiger, dorsal view. Abbreviations: cerc—cercus; d sur—dorsal lobe of surstylus; ej apod—ejaculatory apodeme; epand—epandrium; hypd—hypandrium; hyprct—hypoproct; pgt—postgonite; pgt lb—postgonite lobe; ph—phallus; prens—prensiseta; v epand proc—ventral epandrial process; v sur—ventral lobe of surstylus.

FIGURES 22 – 23. Distribution of Neothalassius gen. nov. 22. Known distribution of Neothalassius triton sp. nov. 22. Known distribution of Neothalassius villosus sp. nov.