The genus Chillcottomyia is distinguished from other genera of Hybotinae by the eyes with dense ommatrichia, wing with broad anal angle, cell cua short, two-thirds length of cell bm and closed by straight vein CuA, cell dm short and broad, and hind femur narrow. The genus can be identified by using the identification key to the genera of Hybotidae in Sinclair and Cumming (2017).

Species of this genus have been described from China, Japan, Nepal and South Africa, with undescribed species known from Indonesia (West Java), Madagascar, Malaysia, Morocco, Philippines, Taiwan and Vietnam (Saigusa 1986; Sinclair and Cumming 2017; Zouhair and Kettani 2022; Sinclair unpubl. data). This is the first report of the genus from Europe.

Holotype • ♂; “Portugal: Porto, Valongo/ 41°09'33.4"N, 8°29'05.6"W/ 30.viii.2018, R. Andrade leg./ CNC2175714”; “HOLOTYPE/ Chillcott­omyia ovaticornis/ Sinclair, Andrade &/ Gonçalves [red label]” (CNC). Paratype: Portugal • 1 ♀; same data as for holotype; Jul. 13 2023; CNC2175715.

The species name is derived from the Latin ovatus (egg-shaped) and cornu (horn), in reference to the ovate-shaped postpedicel.

This small species is distinguished from all other species of the genus, except an un-named species from Morocco by the ovate-shaped postpedicel. The male terminalia is similar to the type species, characterized by left epandrial lamella with subapical dorsal row of stout, stiff setae; right epandrial lamella with outer row of long, stiff setae and inner row of shorter, stout, stiff setae. Male with single, very long anterodorsal seta on mid tibia, female with pair of anterodorsal setae.

Wing length 3.0–3.5 mm. Male. Eyes orange-brown, not flattened dorsally (Fig. 3, as in Fig. 5); upper facets paler and twice as large as darker lower facets, separated by line (Figs 5, 6). Occiput dark brown with grey pruinescence; occipital setae pale. Ocellar triangle elevated, pruinescent, bearing pair of long ocellar setae; distance between posterior ocelli subequal to width of ocellus. Antenna with scape and pedicel brown; postpedicel brown, ovate (as in Fig. 5), slightly projecting dorsally, 2 × as long as basal width; arista-like stylus dark, more than 3 × longer than postpedicel. Proboscis and palpus dark brown.

Scutum strongly arched, dark brown, with pruinescence divided by 4 shiny vittae separating broad central pruinescent band along acrostichals from narrower pruinescent band along dorsocentrals and outer shiny vitta on outer margin of dorsocentral band (as in Fig. 6); postpronotum and postalar callus pale brown; pleura uniformly brown with pruinescence. Chaetotaxy: acrostichals in two biserial rows, thin and short; dorsocentrals uniserial with 1 very long, strong prescutellar dorsocentral seta, shorter than apical scutellum; postpronotum with several long setulae; 1 notopleural seta; 1 postalar seta; 6–7 pairs of scutellar setae, apical pair longest.

Legs yellowish brown, including coxae; tarsomeres 3–5 brown (Fig. 3). Fore femur with anteroventral and posteroventral row of slender setae, latter row longer. Fore tibia broader than mid tibia, with 1 preapical anterodorsal seta, length twice width of tibia and similar posteroventral seta; numerous long, erect slightly shorter dorsal setae; posterior face of long fine setae, subequal to width of tibia; apical third of anterior face with matted setulae. Fore tarsomere slender; tarsomere 1 with dense ventral setae, nearly as long as width of tarsomere. Mid femur with anteroventral and posteroventral row of slender setae, shorter than width of femur. Mid tibia straight; 1 anterodorsal seta on basal half, one-third length of tibia; apex with circlet of long, slender setae, including pair of ventral setae; anterior face with strong setae. Mid tarsus similar to fore tarsus. Hind femur with long posterior and posterodorsal setae on basal half, longer than width of femur; apical half with long anteroventral setae, twice as long as width of femur; apex with circlet of long, slender preapical setae. Hind tibia slightly clavate; 1 long anterodorsal seta on basal half; numerous, long anterodorsal, posterodorsal and anteroventral setae; apex with long anterodorsal and posterodorsal preapical setae; apical third with dense brush of posterior setae. Hind tarsomere 1 slightly broader than remaining tarsomeres; with dense brush of posterior setae, similar to apical third of tibia. Hind tarsomeres 2 and 3 with posterior brush of setae similar to tarsomere 1.

Wing slightly infuscate; pterostigma dark brown, oval; vein R₂₊₃ slightly arched beneath pterostigma; cell dm only slightly broader apically, crossvein dm-m 1.5 × as long as length of apical section of M₄. Halter pale brown.

Abdomen brown, subshiny, clothed in slender pale setae (Fig. 7); tergite 6 without denser and stouter lateral setae; tergite 7 with left lateral setae more than twice as long as right lateral setae; sternites 7–8 with left lateral setae longer than right lateral setae; tergite 8 asymmetrical, divided into two separated sclerites: subtriangular sclerite, tapered to left, produced into slender, sclerotized projection and small triangular sclerite beneath projection, with 2 slender posterior setae; sternite 8 asymmetrical, broadly rectangular, left margin tapered to smaller sclerite of tergite 8. Terminalia (Figs 8–10): Epandrium asymmetrical, left lamella longer and slenderer than shorter and rounded right lamella; right surstylus delimited along inner margin of lamella. Apex of left epandrial lamella arched dorsally with 3 arched, thickened subapical setae (Fig. 8); inner margin with row of some 10 thickened, stiff setae, slightly longer than width of lamella. Right epandrial lamella triangular inflated laterally with surstylus differentiated along inner margin (Fig. 9); outer face with row of 6 thickened setae, longer than width of lamella, and longer than similar setae on inner surstylus. Right surstylus subtriangular with apical row of some 8 thickened setae and clustered row of 6 longer thickened setae. Hypandrium asymmetrical (Fig. 10); posterior margin deeply bilobate, with right lobe longer than left lobe; each lobe with sharp inner ridge extending to apex; right lobe triangular, with line of 3 strong setae and 1 weaker, thin seta; left lobe rounded apically with line of 4 setae. Postgonite flange-like, flattened along inner face with row of subapical setulae. Phallus with pair of ventrally directed hooked processes. Cerci symmetrical, simple, pilose with slender setae; apex without cluster of setae. Hypoproct with pair of short, subapical setae, continuous with slender, elongate subepandrial sclerite.

Female. Similar to male in size (Figs 4–6); leg chaetotaxy longer and denser; pair of very long anterodorsal setae on mid tibia.

This species was collected near the village of Couce (Valongo), in northern Portugal. The female was collected by sweeping vegetation along a small trickle of water near a small river (Ferreira River) (Fig. 2). The surrounding slopes are predominantly covered with eucalyptus stands, while the riverbanks feature patches of native trees, including oaks (Quercus orocantabrica and Quercus suber), willows (mainly Salix atrocinerea), ash trees (Fraxinus angustifolia), and others.

An undescribed species from Morocco (Zouhair and Kettani 2022) is likely conspecific based on the ovate-shaped postpedicel. All other known species of Chillcottomyia are characterized by a conical-shaped postpedicel. The arista-like stylus is supra-terminal in the Portugal specimens but is stated as terminal in Zouhair and Kettani (2022). Confirmation of the identity of the Moroccan species must await discovery of male specimens and comparison of the male terminalia. The row of thickened setae on the left epandrial lamella is very similar to C. septentrionalis Saigusa (see Saigusa 1986, fig. 2), which characterizes a species group within this genus (Sinclair unpubl. data).

The shape of the postpedicel is rather similar to the genus Ocydromia Meigen, but as stated in the key to genera of Afrotropical Hybotidae (Sinclair and Cumming 2017), the wing clearly distinguishes the two genera: pterostigma rounded and dark (elongate and faint in Ocydromia), crossvein dm-m straight (curved in Ocydromia) and R₂₊₃ arched below pterostigma (vein straight in Ocydromia).