Genus Trigoniophthalmus Verhoeff, 1910

Figs. 1–8

Type species: Machilis alternata Silvestri, 1904

Diagnosis. Trigoniophthalmus belongs to the Trigoniophthalmus group of genera, which includes 3 genera: Trigoniophthalmus, Coryphophthalmus, and Trigoniomachilis Stach, 1937 (Sturm & Bach 1993). These genera share the following characteristics: paired ocelli subtriangular, pyriform or of drop-like form, position submedian to the compound eyes; maxillary and labial palps sexually dimorphic with ciliar setae and the third palpomere of labial palps fairly to distinctly widened in male; 2 pairs of exsertile vesicles on urocoxites II–IV or II–V; sublateral macrochaetae on urocoxites IX; urosternites acutely angled; parameres and penis distinctly shorther than urocoxites IX. Trigoniomachilis includes 4 species from Italy, Greece, and Bulgaria (Stach 1937; Mendes 2017). The main differences between these genera are as follows: parameres on urites VIII and IX ( Trigoniomachilis) or only on urites IX ( Trigoniophthalmus, Coryphophthalmus); ovipositor thickened with fossorial spines ( Trigoniomachilis) or long and thin without long setae ( Coryphophthalmus), ovipositor shortened with long setae but without fossorial spines ( Trigoniophthalmus); outer sensorial field in fore femur of male absent ( Coryphophthalmus, Trigoniomachilis) or present ( Trigoniophthalmus). The angle between the axis along the line of contact of compound eyes and the transverse axis of the paired ocellus is about 90° ( Trigoniophthalmus) or less than 90° ( Coryphophthalmus).

Description. Body length 8–13 mm. Hypodermal pigment on head and coxae or absent. Compound eyes black or dark, rounded or widened. Paired ocelli black, submedian, transverse, subtriangular or in the form of a drop (Figs. 1, 2). Angle between the axis along the line of contact of compound eyes and the transverse axis of the paired ocellus about 90°. Mandibles with four typical teeth. Coxal stylets on middle and hind legs. Fore femora of male with small sensorial fields on the external distal part (Fig. 4). Praetarsus without empodial claw. Between claws of pretarsus an apically rounded semi-ellipsoid protrusion with an oval shallow-humped support platform (Fig. 3). Spine-like setae on the ventral surface of tarsus present or absent. Abdominal segments II–IV or II–V with 2 + 2 exsertile vesicles. Urosternites acutely angled. Parameres on the ninth urite, clearly pseudosegmented, with 1 + 5–7 divisions. Male genitalia completely covered by the ninth urocoxites. Ovipositor shortened, not exceeding posterior angle of urocoxite IX or almost attaining middle of styli IX. Anterior gonapophyses with long setae, missing on divisions of posterior gonapophyses or chaetotaxy of posterior gonapophyses similar to that of anterior ones (Figs. 5–8).

Two described subgenera and three species (Table 1).