Marbenia Malloch

Marbenia Malloch, 1931: 31 . Type species: M. peculiaris Malloch, 1931 by original designation. Prado, 1975: 1 –3 (Neotropical catalog); Mathis & Rung, 2011: 350, 352 (world catalog).

Diagnosis. Small flies, body length 2.6–3.5 mm; maxillary palpus short and spatulate; setae of head elongate, postocellar pair well developed; face lacking setae, only a pair of setae on the facial plate, with transverse furrows giving face a wavy appearance; parafacial, gena and occiput with many strong setae; arista bipectinate; two pairs of dorsocentral setae; wing banded; R1 with dorsal setae; R2+3 long and arcuate; M1 almost straight; bm-cu complete; CuA2 lacking; A1+CuA2 extended nearly to wing margin; abdominal tergites 1+2 fused laterally.

Redescription. Body length: 2.6–3.5 mm. Head. Frons with parallel or slightly divergent margins anteriorly and slightly divergent on vertex; face lacking setae, only a pair of setae on the facial plate, internal to the genal row of setae, with transversal furrows giving face a wavy appearance; fronto-orbital plate with series of short setae below fronto-orbital seta; parafacial with well-developed setae, becoming longer and more robust toward ventral region. Buccal structures: palpus flat, short and spatulate, setose on distal half; clypeus U-shaped, microtomentose. Antenna: scape short; pedicel cap-like with dorsal cleft; first flagellomere elongate oval; arista bipectinate with dorsal and ventral rays decreasing progressively in length toward apex intercalated by some shorter rays. All setae conspicuous; ocellar triangle not setulose, ocellar pair well developed; postocellar setae developed and divergent; medial and lateral vertical setae well developed; 1 fronto-orbital long and reclinate. Gena and occiput with many strong setae. Thorax robust, approximately as wide as long (scutellum excluded); subscutellum protuberant; scutum covered with short setae, scutum and scutellum covered with dense pruinescence; 1 postpronotal, 2 notopleural, 1 postsutural supra-alar, 1 postalar, 2 postsutural dorsocentral, 1–3 katepisternal and 2 pairs of scutellar setae. Wing banded; subcosta incomplete; R1 with setulae on dorsal surface; R2+3 long and arcuate; M1 almost straight; M1 and CuA1 extended to wing margin; CuA2 lacking; A1+CuA2 extended nearly to wing margin; cell dm with longitudinal fold. Legs robust; mid tibia with 1 black apicoventral spine; mid tarsus with small black apical spines on ventral surface. Abdomen rather broad, covered by short setae and sparse pruinescence. Tergite 1+2 fused, with transverse unsclerotized region in the middle and longitudinal weak line dividing tergite medially up to membranous area. Male terminalia: symmetrical; sternite 6 well developed, tergite 6 slender; pregenital sclerite (syntergosternite 7+8) reduced to dorsolateral narrow stripe, free from tergite 6 or partially fused with tergite 6, and including spiracle 7; epandrium convex; surstylus undifferentiated; postgonites articulated at anterior margin of hypandrium, partly encircling base of phallus; cercus developed and setose; phallus long, ribbon-like; genital pouch (hypandrium + phallapodeme) large, inflated, slightly sclerotized, forming a bursa-like chamber containing the phallus; hypandrial arms long and fused anteriorly around base of phallus. Female terminalia: tergite 7 and sternite 7 fused, forming a complete ring; tergite 8 and sternite 8 free; sternite 8 broad, slightly concave on anterior margin; tergite 8 convex; cercus small, rounded.

Remarks. The relationships among Periscelidinae genera remain largely unsubstantiated. Ale-Rocha & Freitas (2011) suggested that Marbenia and Neoscutops are closely related based on one putative synapomorphy, vein R1 setulose dorsally. This character state is unique to Marbenia and Neoscutops, and conveniently distinguishes them from other genera in the subfamily Periscelidinae. Marbenia can be distinguished from Neoscutops by two characters: 2 postsutural dorsocentral setae (absent in Neoscutops); veins R2+3 and M1 almost straight (R2+3 and M1 distinctly curved in Neoscutops).

Geographical distribution. Neotropical (Bolivia, Brazil, Ecuador, Panama).