Archaeocerus uenoi Perreau, 2019

Archaeocerus uenoi Perreau, 2019 View in CoL

Description.

Length: 1.2 mm (male) or 1.5 mm (female). Body elongate (Figs 2 View Figures 2–4 , 3 View Figures 2–4 ), flattened (Fig. 4 View Figures 2–4 ), dark brown; antennae, legs, and mouthparts light brown.

Head. Antennal insertions concealed in dorsal view (Fig. 5 View Figures 5, 6 ). Epistomal suture, epistomal stem missing, microreticulation if any, indistinct (Fig. 5 View Figures 5, 6 ). Antennae with 11 antennomeres, 8 th antennomere extremely flat and significantly narrower than 7 th, 9 th, and 10 th, without teeth (Fig. 6 View Figures 5, 6 ). Gular sutures shallow but widely distant. Pronotum transverse, approximately 1.4 × as wide as long, widest very close to the base, with sides regularly arcuate and convergent anteriorly (Fig. 2 View Figures 2–4 ). Surface shiny, with tiny punctures and fine microreticulation, without transverse strigae (Fig. 2 View Figures 2–4 ). Lateral margins with distinct gutter (Fig. 2 View Figures 2–4 ).

Elytra approximately 1.4 × as long as wide jointly, parallel in the two basal third of their length, then regularly rounded at apex. A single parasutural longitudinal stria. Puncture transversely aligned in oblique strigae and associated with short setae (Fig. 2 View Figures 2–4 ). Surface shiny, with no visible microreticulation. Marginal gutter fairly wide (Fig. 2 View Figures 2–4 ).

Flight wings present and probably functional, with nervation present near the base, reduced on the apical half and with numerous microtrichia and with ciliate margins.

Ventral structures. Anterior part of prosternal surface elongated in front of procoxae (Fig. 2 View Figures 2–4 ). Mesoventrum with sharp and uninterrupted longitudinal median carina. Metaventrum not carinate, but with wide medial depression located on top of a medial bulge (as the crater of a volcano). Metaventrite and first abdominal ventrite without setose paired impressions (white spots visible on the ventral surface on Fig. 2 View Figures 2–4 are air bubbles, not setose impressions, without setae). Metacoxae clearly separate.

Legs. Tarsal formula 5-4 - 4 in both sexes (Figs 7 View Figures 7–9 – 11 View Figures 10, 11 ). Female protarsi undilated. Male protarsi imperceptibly dilated, with tenent setae of two kinds on ventral side: some very long and straight, some others shorter, curved and slightly dilated at apex (Fig. 8 View Figures 7–9 ). Their weak contrast in X-rays does not allow visualizing them clearly in microtomography. Meso- and metatarsi undilated and without tenent setae in both sexes (Figs 10 View Figures 10, 11 , 11 View Figures 10, 11 ). Last protarsomere as long as the four preceding ones taken together, last meso- and metatarsomeres as long as the three preceding ones taken together (Figs 10 View Figures 10, 11 , 11 View Figures 10, 11 ). No measurable sexual differences in the relative length of tarsomeres. All tarsi with two interongular setae. Protibias thickened in basal half, bearing in both sexes an area lined with dense bunch of setae on inner margin of apical half (Figs 7–9 View Figures 7–9 ). Outer side of protibias spineless, outer side of meso- and metatibias with strong spines (Figs 10 View Figures 10, 11 , 11 View Figures 10, 11 ).

Aedeagus parallel in two basal thirds then triangularly pointing at the apex in dorsal or ventral view (Figs 12 View Figures 12–15 , 14 View Figures 12–15 ), flat in lateral view (Figs 13 View Figures 12–15 , 15 View Figures 12–15 ). Probably due to the poor state of preservation, the base of the median lobe and of the tegmen is not accurately resolved so that the basal orifice is not visible and the whole median lobe is not exactly symmetrical, slightly deformed. Parameres slightly shorter than the median lobe (Figs 12–14 View Figures 12–15 ), with two subapical distant setae, distal one on the outer side, proximal one on dorsal side (Fig. 19 View Figures 16–20 ). Parameres seemingly disconnected from indistinct basal part of tegmen. Endophallus with wide basal structure with two lateral expansions (Fig. 18 View Figures 16–20 ) and long stylus, roughly cylindrical, not closed on the dorsal side, with more or less gutter shape (Figs 16 View Figures 16–20 , 17 View Figures 16–20 ). A transversal cut taken from one slice of the nano-tomographic reconstruction is shown on Fig. 20 View Figures 16–20 . Flat and 3 D videos of the aedeagus including the endophallus are given in Suppl. materials 1, 2.

Ventrite VIII male and female both with spiculum ventrale (Figs 21–23 View Figures 21–23 ). Male genital segment only partly distinct, making impossible to determine its general morphology. Female genital segment as in Figs 22 View Figures 21–23 , 23 View Figures 21–23 . It is impossible to determine if the lack of visible appendicular parts in the female genital segment and the indistinct male genital segment are an actual depletion or reduction or if it results from the poor state of preservation.