Euconnus (Rhomboconnus) cavifrons

Euconnus (Rhomboconnus) cavifrons (L.W. Schaufuss)

(Figs 1, 9, 16, 19–23)

Scydmaenus cavifrons L.W. Schaufuss, 1866: 38.

Euconnus cavifrons (L.W. Schaufuss); Reitter & Croissandeau 1890: 217; Franz 1967: 697, 715; Franz 1993: 73, fig.42. Euconnus (s. str.) cavifrons (L.W. Schaufuss); Csiki 1919: 46.

Euconnus (Nudatoconnus) cavifrons (L.W. Schaufuss); Franz 1980: 129.

Euconnus (Nudatoconnus) verticicornis Franz, 1980: 122, fig. 99. Synonymized by Franz 1993: 74.

Holotype: Brazil: ♂ (Fig. 1), six historical labels (Fig. 16): “carinifrons / Schauf / Brasilia” [originally white, now darkened, handwritten], “carinifrons / Schauf.” [originally white, now darkened, handwritten], “Brasil” [green, handwritten], “ C. Schaufuss, 1930” [white, printed], “ Holotypus ” [red, printed], “ DEI / Eberswalde” [white, print- ed]; during the present study a new label was added: “ EUCONNUS / (RHOMBOCONNUS) / carinifrons / (L.W. Schaufuss, 1866) / det P. Jałoszyński, 2020” [white, printed] (SDEI).

Emended diagnosis. Male head stout, with narrowly projecting and distinctly emarginated posterior margin of vertex; vertex with longitudinal median impression and two posterior tufts of setae, additionally each temple with slender tuft of setae behind middle; tempora distinctly rounded; pronotum subconical, broadest at base and indistinctly elongate, lacking antebasal pits, groove and sublateral carinae; dorsum sparsely setose; antennomeres VII–X elongate; aedeagus with ventral plate in distal half gradually narrowing distad; endophallus with conspicuously short sclerites, of which the longest is narrow and pointed at apex, with symmetrical distal half.

Redescription. Body of male (Fig. 1) strongly convex, elongate, with moderately long and slender appendages, BL 2.13 mm; cuticle glossy, uniformly dark reddish-brown, vestiture yellowish.

Head (Fig. 9) relatively short, strongly narrowing posteriorly, broadest at eyes, HL 0.50 mm, HW 0.43 mm; vertex and frons confluent, frons evenly convex, vertex with distinct median longitudinal impression with diffuse margins, posterior margin of vertex narrower than half HW and distinctly concave at middle; tempora about 3 × as long as eyes in dorsal view, strongly rounded in anterior half and slightly sinuate posteriorly; supraantennal tubercles weakly marked; eyes large, finely faceted and weakly projecting from silhouette of head. Punctures on vertex and frons very fine and inconspicuous; thin setae extremely short and sparse, so that under magnifications of stereomicroscope up to 100 × head appears asetose, additionally posterior margin of vertex with two tufts of thick bristles separated by posterior emargination, and each temple with long tuft of bristles behind middle. Antennae slender but relatively short, AnL 1.15 mm; all antennomeres except III distinctly elongate, III slightly transverse; antennomere XI indistinctly flattened, distinctly shorter than IX–X together, nearly twice as long as broad.

Pronotum (Fig. 9) in dorsal view subconical and broadest at base, strongly narrowing anteriorly, PL 0.50 mm, PW 0.53 mm; sides indistinctly rounded (nearly straight), anterior margin nearly straight, posterior margin weakly arcuate; base lacking pits, grooves and carinae. Punctures inconspicuous; pronotal disc virtually asetose, sides with thick bristles.

Elytra together suboval, broadest distinctly in front of middle, EL 1.13 mm, EW 0.88 mm, EI 1.29; apices rounded together. Punctures on elytral disc slightly more distinct than those on head and pronotum, but small, superficial and sparse, inconspicuous; elytra covered sparsely with very thin, short, suberect setae.

Legs moderately long and slender; unmodified.

Aedeagus (Figs 19–23) stout, AeL 0.40 mm, in ventral view drop-shaped and gradually narrowing toward apex; endophallus with conspicuously small complex of sclerites (Fig. 23), of which the longest is slender and nearly symmetrical, with narrow, pointed apex; parameres slender, each with three long apical and subapical setae and additionally with one tiny seta far from apex.

Female. Unknown.

Distribution. Brazil; exact locality for the holotype unknown; E. verticicornis, which is a junior synonym of E. cavifrons, was collected in Barueri near São Paulo.

Remarks. This species was treated as Euconnus s. str. by Csiki (1919), as Euconnus (Nudatoconnus) by Franz (1980), and as Euconnus incertae sedis by Franz (1967, 1993). The unique structure of the head (including the ventral longitudinal groove) and the aedeagus (unusually uniform in all species of this subgenus) clearly support its placement in Rhomboconnus.

The median longitudinal impression on the vertex and four tufts of setae (two on vertex and two on tempora) are unique for E. cavifrons. The subconical pronotum with nearly straight lateral margins is also rarely found among species of Rhomboconnus; besides E. cavifrons, only E. perplexus Franz and E. wari Jałoszyński have a similar form of the prothorax. However, E. perplexus and E. wari have the pronota and elytra covered with long setae, the vertex lacking two tufts of setae, differently shaped heads, the pronota not elongate, and clearly different genital structures.