Chimerothalassius runyoni, Brooks & Cumming, 2018

Brooks, Scott E. & Cumming, Jeffrey M., 2018, New species of Chimerothalassius Shamshev & Grootaert (Diptera: Dolichopodidae: Parathalassiinae) from the West Indies and Costa Rica, Zootaxa 4387 (3), pp. 511-523 : 513-516

Chimerothalassius runyoni sp. nov.

( Figs 1 –9, 11–16, 19–21)

Type material. HOLOTYPE ♂, labelled: “ WEST INDIES: MONTSERRAT / Woodlands Beach / rocks in intertidal zone/ N16°45.817′ W62°13.384′ / 21 JUNE 2017, JB Runyon ”; “ HOLOTYPE / Chimerothalassius runyoni / Brooks & Cumming [red label]” ( CNC) . PARATYPES: MONTSERRAT: same data as holotype (1♂, 3♀, CNC) ; same data as holotype except, 22.vi.2017 (2♂, CNC) ; same data as holotype except, 20.vi.2017 (10♀, CNC).

Other material examined. DOMINICA: Saint Joseph Parish: Layou River mouth [ca. 15°23.7′N 61°25.5′W], 9.i.1965, W.W. Wirth, sea shore, Bredin-Archbold Smithsonian Biological Survey , Dominica (1♀, USNM) ; Saint Joseph Parish, Rodney’s Rock [ca. 15°22.818′N 61°24.707′W], 5.ii.1964 [H. Robinson] (slidemounted wing, USNM) .

Diagnosis. Chimerothalassius runyoni sp. nov. is distinguished from other known species of the genus by the following combination of features: body brown; head with lower 6–7 postocular bristles strong, long and pale ( Figs 2–4 ); palpus elongate and narrow with pair of elongate preapical ventral bristles; legs infuscate distally with coxae, trochanters and basal half of femora yellow; fore coxa with row of 3 long fine pale setae on anterior surface ( Fig. 5 ); fore femur with 1 strong pale basiventral bristle; wing about 2.7X longer than wide, with basal portion of costa bearing group of 3–4 bristles above branching point of R2+3 and R4+5 (Figs 7–9); costal section between R2+3–R4+5 subequal to R4+5–M1 section; male terminalia with phallus bifurcate, cercus subtriangular in dorsal view, right and left cerci symmetrical ( Figs 11–13 ).

Description. Male. Wing length 1.15–1.25 mm (holotype and male paratypes). Body (cf. Fig. 2 ) dark brown; legs infuscate distally with coxae, trochanters and basal half of femora yellow; major bristles of head (i.e., frontoorbitals, anterior ocellars, postocellars, verticals) and thorax (i.e., dorsocentrals, supra-alars, notopleurals, postalars, scutellars) black unless otherwise noted, other smaller setae dark unless otherwise noted. Head ( Figs 3– 4 ): Dark grey-brown. Broader than thorax in dorsal view; ovoid, slightly broader than high in lateral view ( Fig. 4 ), about 1.6X broader than high in anterior view ( Fig. 3 ). Neck inserted slightly above middle of head. Ocellar triangle conspicuous. Occiput weakly concave on upper median part above occipital foramen. Dichoptic; eyes entirely covered with ommatrichia, medial edge with emargination adjacent to antenna, ommatidia progressively smaller anterodorsally, eye ovoid in lateral view, broader than high, posteroventral margin straight. Frons dark grey-brown, nearly 4X broader than high, widening above. Face and clypeus concolourous with frons. Face narrowest at middle, about 2.0X width of anterior ocellus. Clypeus with upper margin delineated from face, broader than high, widening below, lower margin truncate, ending above lower margin of eyes. Gena very narrow. Postgena narrow. Bristles of head well-differentiated, each side with: 1 fronto-orbital bristle close to base of antenna, 1 anterior ocellar bristle, 2 short posterior ocellar setae; 1 postocellar bristle, 1 vertical bristle; 2 postvertical bristles; postocular setae arranged in single row, upper 3–4 setae short and dark, lower 6–7 bristles strong long and pale. Antenna ( Figs 3–4 ) brown, inserted above middle of head in profile; scape short, funnelshaped; pedicel larger and slightly longer than scape, spheroidal with subapical circlet of setulae; postpedicel about 2X longer than wide, bulb-shaped with rounded basal half and strongly tapered and narrowed distal half, clothed in fine hairs; stylus arista-like, about 3X longer than postpedicel. Palpus brown, elongate and narrow, clothed with minute pile, apical portion setose with pair of long pale preapical ventral bristles, sensory pit absent. Proboscis directed posteriorly with broad fleshy setose labellum, pseudotracheae indistinct. Thorax: Dorsum dark brown, pleuron dark brown-grey. Mesoscutum moderately arched, prescutellar depression present. Prosternum fused with proepisternum forming precoxal bridge. Proepisternum with lower bristle. Postpronotal lobe distinct with 1 small seta. Mesonotum shield-shaped in dorsal view, slightly longer than wide. Acrostichal setae absent; other bristles of thorax well-differentiated, each side with: 4 strong dorsocentral bristles with 1 small seta between some bristles, 1 small presutural supra-alar seta (close to anterior notopleural bristle), 1 strong postsutural supra-alar bristle with small seta anteriorly, 2 strong notopleural bristles sometimes with 1 small seta in-between, and 1 small postalar seta; scutellum broadly subtriangular with pair of strong erect inclinate bristles near apex. Mesopleuron bare. Halter with dark brown knob and yellow stem. Legs: Coxae and trochanters yellow; femora yellow in basal half, infuscated apically; tibiae and tarsi infuscated; coxae and trochanters with pale setae; femora, tibiae and tarsi mostly clothed with dark setae, devoid of well-differentiated bristles (except foreleg); tarsal claws, pulvilli and empodium normally developed on all legs; tarsomere 5 of fore, mid and hind legs with medial apical projection ( Fig. 6 ). Foreleg ( Fig. 5 ): Coxa with row of 3 long fine pale setae on anterior surface; femur with 1 strong pale basiventral bristle; tibia slightly shorter than femur, with apical comb-like row of closely-spaced setae on anterior surface; tarsus subequal in length to femur; tarsomere 1 shorter than combined length of tarsomeres 2–5; tarsomere 2 and 3 subequal, tarsomere 4 shorter; tarsomere 5 slightly longer than tarsomere 2. Midleg: Coxa with 2 anterior setae and 1 anterolateral seta; femur subequal in length to tibia, tarsus slightly longer; tibia with short apicoventral bristle; tarsomere 1 subequal to combined length of tarsomeres 2–5; tarsomeres 2–4 decreasing in length apically; tarsomere 5 subequal in length to tarsomere 2. Hindleg: Coxa with 1 anterior seta and 2 setae on lateral surface; femur slightly longer than tibia; tibia with apical comb-like row of closely-spaced setae on posterior surface; tarsus subequal in length to femur; tarsomere 1–4 gradually decreasing in length apically; tarsomere 5 subequal in length to tarsomere 3. Wing (Fig. 9): Hyaline, veins brown, about 2.7X longer than wide. Pterostigma absent, membrane entirely covered with minute microtrichia, alula absent. Costa (C) circumambient with strong bristle at extreme anterior base (cf. Figs 7–8), basal portion with 1 anterodorsally projecting and 2 dorsally projecting bristles above branching point of R2+3 and R4+5. Anterior section of costa (between base and R4+5) bearing double row of spine-like setae. Posterior section of costa (i.e., beyond R4+5) with setae finer and longer. Longitudinal veins complete, reaching wing margin. Sc faint. R1 straight, running very close to C for most of its length, reaching costa before middle of wing, well before termination point of M4. R2+3 diverging from R4+ 5 in basal part, gradually curved posteriorly to run subparallel to R4+5 for most of length. R4+5 nearly straight. M1 diverging from R4+5, nearly straight with slight posterior curve in apical portion. Costal section between R2+3–R4+5 subequal to R4+5–M1 section. M2 absent. M4 diverging from M2, mainly straight with slight posterior curve in apical portion. Base of Rs originating opposite humeral crossvein. Crossvein r-m indiscernible. Crossvein bm-m appearing incomplete, depigmented at junction point with M1. Crossvein dm-m and cell dm absent. Cells bm and cua small, near base of wing, subequal in length and width. Cell cua closed with distal end rounded. Vein CuA+CuP absent. Calypter with fine seta. Abdomen: Dark brownish black. Abdominal plaques present, prominent on lateral margins of tergites 2–4; tergite and sternite 2 with transverse band of plaques anteriorly. Tergites 1–6 and sternites 1–5 with short setae along posterior surface, otherwise mostly bare, sternites 4 and 5 with some longer setae, sternite 6 bare. Segment 7 bare. Segment 1 reduced and very short; segments 2–4 mostly symmetrical with simple tergites and sternites, segment 2 relatively long; segments 5–7 narrowed and laterally compressed to form cavity on right side for hypopygium. Sternite 5 reduced to narrow band-like sclerite along anterior and lateral margins, without projecting pregenitalic process. Tergite 7 narrower than sternite, with broad posteromedial emargination. Sternite 8 suboval, forming dome-like cap over anterodorsal region of hypopygium, with pair of strong setae on posterior half and several short setae near base; tergite 8 indistinct. Hypopygium ( Figs 11–13 ): Brown with cerci and other projecting sclerites pale. Lateroflexed to right; inverted with posterior end directed anteriorly; small and compact, about 1/4 length of abdomen; asymmetrical; foramen not formed. Epandrium divided into left and right lamellae. Left epandrial lamella ( Fig. 11 ) partially overlapping left side of hypandrium, posterior margin trifurcate, ventral margin fused with hypandrium but epandrial margin distinct; ventral epandrial process present, apparently not articulated at base, elongate with acute hooked apex. Left surstylus bilobed, dorsal and ventral lobes separated by deep U-shaped cleft through which left postgonite lobe protrudes. Dorsal lobe of left surstylus broad with rounded apex, with large preapical dorsal seta, slightly larger subapical seta and tiny apical seta, lacking prensiseta. Ventral lobe of left surstylus narrow, as long as dorsal lobe, with short apical seta and similarly-sized seta lateroventrally. Right epandrial lamella ( Fig. 12 ) partially overlapping right side of hypandrium, subrectangular, fused with hypandrium along lower margin, ventral epandrial process absent. Right surstylus bilobed, dorsal and ventral lobes separated by deep U-shaped cleft through which right postgonite lobe protrudes. Dorsal lobe of right surstylus broad with rounded apex, with large preapical dorsal seta, subequal subapical seta and small apical seta, lacking prensiseta. Ventral lobe of right surstylus digitiform, about 2X longer than dorsal lobe, basal margin with 3 long setae, with short setae near apex. Hypandrium bowl-shaped. Postgonite with basal internal portion cradling base of phallus and ejaculatory apodeme, left and right postgonite lobes large and protruding out from between dorsal and ventral lobes of surstylus. Left postgonite lobe broad with dorsal seta near middle and long narrow curved tip. Right postgonite lobe similar to left lobe but with shorter tip. Phallus tubular, J-shaped, bent upwards, bifurcated near midlength with shorter narrow ventral branch. Ejaculatory apodeme rod-like. Hypoproct ( Figs 11–13 ) projected as a pair of broad apically rounded symmetrical lobes. Cercus ( Figs 11–13 ) small with acute apex, subtriangular in dorsal view, with strong inclinate preapical seta and 2–3 adjacent setae, right and left cercus symmetrical.

Female ( Fig. 2 ). Wing length 1.35–1.50 mm (female paratypes). Similar to male except as follows: Legs: Coxae and femora infuscated, concolourous with tibiae and tarsi. Abdomen: Tapering posteriorly, apical segments retracted into segment 5. Terminalia ( Figs 14–16 ) with tergite 8 medially divided, narrowly fused with sternite 8 anterolaterally; tergite 10 medially fused with three acanthophorite setae on each side; cercus narrow blunt-tipped with long preapical ventral seta and several short setae; spermathecal duct an unsclerotized tube with broad ridged sperm pump in basal part and conical terminal expansion.

Etymology. The species name honours our colleague and fellow empidoid worker Dr. Justin B. Runyon, who collected the type series from Montserrat.

Distribution. Chimerothalassius runyoni sp. nov. is currently known to occur along rocky intertidal zones on the western coastlines of Montserrat and Dominica ( Figs 19–21 ).

Remarks. Chimerothalassius runyoni sp. nov. was initially reported from Dominica (as Chimerothalassius sp.) by Brooks & Cumming (2011, pp. 44 3–444), based on W.W. Wirth’s female from the Layou River mouth ( Fig. 2 ) and H. Robinson’s slide-mounted wing (sex unknown) from Rodney’s Rock (Fig. 7). The Dominica specimens appear virtually identical to the specimens from Montserrat, although they are slightly larger (wing length 1.45– 1.60 mm). Robinson (1975, p. 2) stated that many species of Dolichopodidae sensu stricto found in the Lesser Antilles are widely distributed through the islands, especially those occurring in marine habitats. We are currently treating the specimens from both islands as conspecific, but this will require additional confirmation through at least discovery of male specimens from Dominica.

Both the male ( Fig. 4 ) and female palpus and foreleg of C. runyoni sp. nov. are not dimorphic in terms of chaetotaxy, as was described and figured for C. ismayi by Shamshev & Grootaert (2002, figs 3–4, 11–12) (but see Remarks under Chimerothalassius above).

Figures

FIGURE 19. Known distribution of New World Chimerothalassius species.

FIGURES 20–22. Detailed distribution maps of New World Chimerothalassius species. 20. Collection locality of Chimerothalassius runyoni sp. nov. on Montserrat. 21. Collection localities of Chimerothalassius runyoni sp. nov. on Dominica. 22. Collection localities of Chimerothalassius sp. on west coast of Costa Rica. Map data: Google, DigitalGlobe. Scale bar = 10 km.

FIGURES 1–2. Type locality habitat photograph and female habitus of Chimerothalassius runyoni sp. nov. 1. Rocky coastal type locality at Woodlands Beach, Montserrat (photo by Justin Runyon). 2. Female specimen from Layou River mouth, Dominica collected by W.W.Wirth, January 9 th, 1965.

FIGURES 3–4. Chimerothalassius runyoni sp. nov., male head. 3. Anterior view. 4. Lateral view. Abbreviations: frorb sfronto-orbital bristle; lbl—labellum; plp—palpus.

FIGURES 5–6. Chimerothalassius runyoni sp. nov., foreleg. 5. Male left foreleg, posterior view. 6. Female left foreleg, apex of tibia and tarsus, dorsal view. Abbreviation:tsm—tarsomere.

FIGURES 11–13. Male hypopygium of Chimerothalassius runyoni sp. nov. 11. Left lateral view. 12. Right lateral view. 13. Cerci, dorsal view. Abbreviations: cerc—cercus; d sur—dorsal lobe of surstylus; ej apod—ejaculatory apodeme; epandepandrium; hypd—hypandrium; hyprct—hypoproct; pgt lb—postgonite lobe; ph—phallus; v epand proc—left ventral epandrial process; v sur—ventral lobe of surstylus.

FIGURES 14–16. Female terminalia of Chimerothalassius runyoni sp. nov. 14. Spermatheca. 15. Dorsal view. 16. Lateral view.Abbreviations:cerc—cercus; spmth—spermatheca; st—sternite; tg—tergite.