Arthmius menguali sp. nov.

Figs 2P–R, 3F, 4K–L

Type material. Holotype ♂ (MECN-EN 40941): “ ECUADOR: Napo, -0.5952°, -77.8994°, Est. Biol. Yanayacu, Piha Tr., 2386m, 9.IX.2024, sifted litter, M.Caterino ” / “Caterino DNA voucher, Ext. MSC-12947, Morphosp. Yn.A.016”; deposited in MECN. Paratypes (2♂): same locality as type (MECN-EN 40942–40943).

Diagnosis. (TL: 2.2mm) Body orange, smooth, with sparse short, recumbent setae and scattered much longer, erect setae; male head roundly widened in front of eyes, depressed on either side of an interrupted median longitudinal carina (Figs 2R, 3F), posteriorly acute behind interruption, forming a diminishing ridge anteriorly; antennae moderately elongate, antennomeres II–IV barely longer than wide, V & VII about twice as long as wide, slightly swollen on inner edge, VI & VIII shorter, IX–XI forming loose club; pronotum with weak lateral foveae and weak, straight transverse sulcus; elytra rounded at sides, narrow anteriorly, each with three dorsobasal foveae; subhumeral foveae absent, subhumeral stria weak; abdominal segments with single lateral marginal carina; legs and venter lacking obvious secondary sexual characters. Aedeagus (Fig. 4K, L) with low basal bulb broadly open ventrally and dorsally, thicker (dorsoventrally) at base, narrowed apicad; tegmen extended from right of center, dorsoventrally flattened at base, then twisted into apically laterally flattened blade, blade bent ventrad toward square apex; tegmen with a conspicuous, rounded dorsal lobe at its base.

Etymology. I name the species in recognition of the camaraderie of dipterist Dr. Ximo Mengual on this field trip. Dr. Mengual suggested I sample along the trail that yielded this species.

Distribution. This species is known only from the cloud forests of Yanayacu Biological Station, at about 2000m in the Napo Province of Ecuador.

Remarks. This species is best recognized by the interrupted male frontal carina.