Bregmosina, Marshall, Stephen A., 2013

Marshall, Stephen A., 2013, Bregmosina, a new Neotropical genus of Limosininae (Diptera: Sphaeroceridae), Zootaxa 3641 (3), pp. 260-270 : 261

Bregmosina new genus

Type species: Bregmosina bucki new species

Generic diagnosis. S hining brown Limosininae with a conspicuously broad head and swollen face; face higher than frons; frons with only a single very large, cruciate pair of interfrontal bristles (sometimes also with inconspicuous setulae below). Fore tarsomeres short and broad; tarsomeres one and two of hind leg swollen. Wing with R4+5 ending well before wing tip, costa extending far beyond end of R4+5; discal cell with a strong longitudinal fold. Katepisternum with only minute bristles. Female with tergite 10 (epiproct) absent. Male with middle part of sternite 5 extensively modified to form part of the genital pouch, effectively isolating lateral portions of sternite.

Generic description. Shining brown, length 2.0– 2.4 mm, wing length 1.5–1.6 mm. Supra-alar area yellow to pale brown, contrasting with the darker brown scutum and scutellum.

Head: Head broad and short, face evenly bulging and slightly higher than frons, clypeus linear and oral cavity conspicuously large. Frons with a single very large pair of cruciate interfrontal bristles and usually with one or two minute lower interfrontal setulae (never with interfrontal bristles or setulae above large cruciate pair). Two orbital bristles, lower smaller. Ocellar bristles large, as large as upper orbital, inserted outside margins of ocellar triangle. Postocellar bristles minute, inner and outer vertical bristles large. Antennae very widely separated (interantennal distance 0.7X height of face), scape with a large proclinate bristle, first flagellomere slightly pointed with arista slightly preapical. Arista long-pubescent (hairs 3X width of first aristomere), very long (slightly longer than head plus scutum). Eye 2.0–2.8X genal height at narrowest point of gena. Vibrissa very large, subvibrissa distinct, anterior genal bristles slightly enlarged.

Thorax: Prosternum linear, bare. Scutum with strong postpronotal, notopleural, supraalar and postalar bristles. Supraalar area depressed, projecting over wing base. Dorsocentral bristles in 2 postsutural pairs, anterior dorsocentrals small with 6–7 acrostichal bristles between them, posterior dorsocentrals large and with a pair of enlarged prescutellar acrostichals between them. Scutellum with 4 marginal bristles, disc bare. Katepisternum with only minute dorsal bristles, usually two.

Foreleg with tarsomeres 2–4 or 3–4 broad and short, flattened in some species; mid tarsus unmodified; hind tarsus with first and second tarsomeres strongly to moderately swollen, distal tarsomeres short, flat and quadrate. Tarsal claws cultriform. Fore and hind femora slightly swollen, mid femur slender. Mid tibia with only an apical ventral bristle in both sexes (two apical ventral bristles in B. schizosterna ), dorsally with a proximal anterodorsal bristle, three large distal bristles (anterodorsal, dorsal, posterodorsal) and sometimes a smaller dorsal bristle proximal to large distal dorsal. Wing with costa extending well beyond apex of R4+5. Crossvein dm-cu as long as portion of costa beyond apex of R4+5. Crossvein r-m about half as long as dm-cu.

Male abdomen: All sternites modified in some species, fifth sternite mostly or entirely longitudinally divided. Hypandrium with broad posterior arms exposed under anteroventral corners of epandrium, not fused with epandrium. Cerci fused or contiguous basally, usually divergent distally. Surstylus, postgonite and phallus interspecifically variable, but surstylus usually with an anteroventral point or process. Synsternite 6–8 usually subtending invaginated posteromedial portion of sternite 5 to make a deep genital pouch; sternite 8 dorsally fused with S7 but separate from epandrium. Ring sclerite present but incomplete in some species.

Female abdomen: Syntergite 1+2 large, dark except for anteromedial section. Tergites 3, 4 and 5 each paler and less than half as long as syntergite; tergites 6 and 7 longer, tergite 8 interspecifically variable, tergite 10 (epiproct) absent. Cerci short with a long apical bristle. Sternites pale except sternites 6, 7 and 8; sternite 8 large.

Similar genera: Bregmosina is highly distinctive, and has been informally recognized as an isolated group of unknown generic affinities for over 20 years, during which time material of this infrequently collected group has slowly accumulated. The most similar genera are Druciatus and Sclerocoelus , both described by Marshall (1995). Druciatus species also have strongly cruciate interfrontal bristles but lack the bulging face and other defining characters of Bregmosina . There is no indication that these genera are closely related. Sclerocoelus is a very large genus of mostly undescribed species, many of which have a bulging face superficially like that of Bregmosina . Sclerocoelus species, however, have a very complicated genital pouch and no similarities to Bregmosina in other genitalic characters. There are no clear synapomorphies linking Bregmosina to other limosinines, which is precisely why it warrants description as a new genus.