Micranops brunneus Cameron, 1913: 350

Herman, Lee, 2023, Generic Revisions Of The Scopaeina And The Sphaeronina (Coleoptera: Staphylinidae: Paederinae: Lathrobiini), Bulletin of the American Museum of Natural History 2023 (460), pp. 1-195 : 121-131

Micranops brunneus Cameron, 1913: 350 ,

fixed by monotypy.

— Cameron, 1923: 400 (correction of original description). — Scheerpeltz, 1933: 1271 (catalog). — Blackwelder, 1939a: 98, 105, 119 (key; checklist; type species). — Blackwelder, 1944: 119 (checklist of species, Latin America). — Blackwelder, 1952: 243 (type species). — Blackwelder and Arnett, 1974: 57 (checklist; North America; Central America; West Indies). — Frisch, Burckhardt, and Wolters, 2002a: 35, 45, 46 (characters; included in phylogenetic analysis of Scopaeina species of Western Palaearctic; notes; synonymy).

— Frisch, Burckhardt, and Wolters, 2002b: 1 (catalog). — Smetana, 2004: 615 (Palaearctic catalog). — Frisch and Oromí, 2006: 23 (characters; discussion; taxonomic history; three new species; discussion of endogean and troglobitic species). — Frisch and Herman, 2014: 67 (checklist, original reference and distribution of species; one new species).

Nivorus Herman, 1965a: 119 . Type species: Orus cameroni Blackwelder, 1943: 278 , fixed by original designation.

— Blackwelder and Arnett, 1974: 57 (synonym of Orus ). — Newton, Thayer, Ashe, and Chandler, 2000: 386 (subgenus of Orus ).

— Navarrete-Heredia et al., 2002: 279 (subgenus of Orus ; unnamed species known from Mexico). — Frisch, Burckhardt, and Wolters, 2002a: 45, 46 (synonym of Micranops ; type species). — Frisch, Burckhardt, and Wolters, 2002b: 1 (synonym of Micranops ; type species). — Smetana, 2004: 615 (synonym of Micranops ). — Frisch and Herman, 2014: 68 (synonym of Micranops ).

Microscopaeus Coiffait, 1981: 19. Type species: Scopaeus microphthalmus Eppelsheim, 1888: 409 , fixed by original designation.

— Coiffait, 1984: 148 (subgenus of Scopaeus ; key to species). — Frisch, Burckhardt, and Wolters, 2002a: 45, 46 (synonym of Micranops ; type species). — Frisch, Burckhardt, and Wolters, 2002b: 1 (synonym of Micranops ; type species). — Smetana, 2004: 615 (synonym of Micranops ). — Frisch and Herman, 2014: 68 (synonym of Micranops ).

DIAGNOSIS: Micranops is separated from all other Scopaeina by the unique form and position of the trichobothrial cavity on the lateral side of the head behind and separated from the posterior margin of the eye (figs. 266, 267, 282). The trichobothrial depression or canal of all other genera of the Scopaeina touches the dorsal margin of the eye (figs. 11, 13–15, 334).

DESCRIPTION: Body length 1.8–5.1 mm.

Head with postocular lateral margin broadly and shallowly (fig. 259, 272, 282) to strongly curved to basal angles; basal angles broadly ( Frisch and Oromí, 2006: figs. 1, 2) to sharply (fig. 259, 272, 282) rounded or head elongate with broadly rounded lateral margins ( Frisch and Oromí, 2006: fig. 4a); basal margin truncate to broadly and shallowly emarginate (fig. 272) to slightly rounded and without median tumescence; posteroventral surface without tubercles.

Neck wide, moderately constricted at nuchal groove and gradually expanded at occiput and not petiolate (fig. 272) or petiolate and strongly constricted at nuchal groove and abruptly expanded at occiput (species of Eastern Hemisphere); nuchal groove moderately deep to deep; neck width across nuchal constriction one to two fifths as wide as greatest postocular width of head; nuchal ridge present dorsally and laterally (fig. 266).

Dorsal surface of head with fine, dense to moderately dense punctation; punctation denser laterally than medially and punctation most sparse midanteriorly; punctation distinct or obscured by strong microsculpturing; microsculpturing dense and uniform to present only near margins; surface dull to strongly shining to polished; pubescence fine and dense, moderately dense; macrosetae short, peripheral, and few.

Cephalic trichobothrium present as small, deep cavity on lateral side of head behind and separated from eye (figs. 267, 282); for eyeless species, behind normal position of eye; trichobothrial cavity with setae around periphery of inner surface (figs. 268, 269); bothrium positioned near middle of cavity (fig. 269).

Eyes with posterior margin broadly to more narrowly rounded; corneal lenses with (fig. 19) or without (fig. 18) sensilla.

Gular sutures moderately widely separated (fig. 272, sutures visible through integument as diffuse, gray shadows).

Mandibles: right mandible with three or four denticles, left with three (fig. 263).

Labrum bidentate (fig. 265; some might regard as denticles the rounded lobes laterad of submedial denticles).

Pronotum broadly and shallowly convex to nearly flat; surface with fine to moderately coarse punctation; punctation dense to moderately dense, uniform, and obscured by microsculpturing in many species; microsculpturing dense and uniform or present near margins; midlongitudinal strip impunctate; surface dull to moderately shiny to polished; pubescence fine and dense to moderately dense; macrosetae short, peripheral, and few; median groove present on posterior half and distinct to feeble; posterior margin straight to slightly emarginate.

Prohypomeron without transverse, prohypomeronal ridge; postprocoxal lobe with few setae.

Notosternal suture present (fig. 260) or absent.

Elytra longer or shorter than pronotum; surface punctate; pubescence dense to moderately dense; posterior margin with row of setae.

Mesoventrite with broad, shallow, median, basisternal depression (fig. 276); prepectal ridges medially separated; mesotransventral ridge present medially only; mesanapleural ridge with anterior segment present, posterior segment poorly developed.

Mesofurcasternum without (figs. 273, 276) internal, median apophysis on posteromedial margin.

Mesofemur without plectral ridges (fig. 277).

Mesocoxal acetabulum margined by pericoxal ridge (figs. 270, 280).

Metaventrite without stridular file (figs. 270, 271; 280, 281).

Metakatepisternal process short, about as wide as long, apically acute, lateral margin diagonally directed to meet medial margin and sharply rounded apically (fig. 270).

Sternite II (fig. 284) without median point on posterior margin.

Sternite III without median carina; transverse basal ridge weakly sinuate, and with moderately long, triangular, median point (fig. 284).

Sternite IV without glandular opening or lobe (fig. 278).

MALE: Sternite VII with surface variously modified or unmodified; posterior margin with median emargination of varying depth, width, configuration.

Sternite VIII with wide to narrow, shallow to deep median emargination (see Frisch and Oromí, 2006: figs. 12, 14)

Tergite IX (fig. 261) slightly asymmetrical: left anteroventral side slightly larger and wrapping medially slightly more than right; posterior margin with basal edge of emargination flat to shallowly to strongly curved; middorsal base fused medially (fig. 261).

Tergite X (fig. 261, 285) trapezoidal; anterior margin wide and moderately rounded to nearly straight and without median point.

Aedeagus (figs. 274, 275; see Frisch and Oromí, 2006: figs. 7, 10) with dorsal surface of median lobe midlongitudinally divided; parameres absent.

FEMALE: Sternite VII unmodified.

Sternite VIII with rounded posterior margin.

Tergite IX (see Frisch and Oromí, 2006: figs. 15, 18) symmetrical, left and right anteroventral sides of approximately equal size; posterior margin with deep U-shaped emargination, anterior margin of emargination strongly to more gradually rounded; middorsal base fused medially.

Tergite X (see Frisch and Oromí, 2006: figs. 15, 18) with anterior margin slightly concave or slightly to strongly rounded to lateral margin; anterior margin without median point.

DISTRIBUTION AND HABITAT: Micranops is known from tropical and subtropical regions around the world with one species, M. pilicornis , reaching the periphery of more temperate locales (see Frisch and Herman, 2014: 70). New World species are found across the southern United States south through the West Indies and Mexico south into northern Argentina. In the Caribbean species are known on four West Indian islands: Cuba, Jamaica, Hispaniola, and Grenada. In the Old World species have been collected from the Canary Islands eastward to Italy and southern Europe and across the Middle East and the Caucasus to Turkmenistan on to India, Sri Lanka, the Malay Peninsula, the Philippines, Taiwan, and Australia, and in Africa from Egypt to tropical and southern Africa. Most species are known from one or a few localities and most specimens in collections are unnamed. Micranops pilicornis , found from Italy east to the Balkans, Cyprus, Turkey, the Middle East, Iran, southern Russia, and Turkmenistan, has the widest known distribution of any in the genus ( Frisch and Oromí, 2006: 24; Frisch and Herman, 2014: 70). As of this writing, to my knowledge, M. pilicornis has not been reported from mainland Spain.

Based on specimen label data and published accounts, the following is known about the potential habitat for species of Micranops . Species have been found in the lowlands and high montane regions, some to as high as 2000 and 2200 meters in the Democratic Republic of the Congo for M. lwiroensis ( Fagel, 1973) and M. aborensis ( Fagel, 1973: 32, 33) and 2450 meters on Tenerife, Canary Islands, for M. mlejneki ( Frisch and Oromí, 2006: 30) . According to label data, they have been collected from forest-floor leaf litter and humus, near streams, from epiphytic humus, log mold and debris, flood debris, and at light traps. Specimens of M. cameroni were collected from under seaweed in Jamaica ( Blackwelder, 1943: 279). Frisch and Oromí (2006: 35) wrote that most species of Micranops inhabit the interstices of the upper layers of moist sandy or gravelly soil, often near streams. Frisch and Oromí (2006: 35) reported Micranops pilicornis , a widespread southwest Eurasian species, has been repeatedly collected near running water under deeply embedded stones or up to about 20 cm deep in sandy or gravelly banks. In the same article they described or redescribed three endogean and one troglobitic species. Micranops spelaeus Frisch and Oromí, 2006 , the only troglobitic species reported for the Scopaeina and represented by a single specimen, was collected from the Canary Islands on Tenerife; at 5.1 mm, it is also the largest known species of the genus. Two other species described from the Canaries, M. bifossicapitatus Outerelo and Oromí, 1987 , and M. mlejneki Frisch and Oromí, 2006 , were collected in caves, the latter also from under an embedded rock. Both are considered endogean species and in caves only because of the aridity of the islands ( Frisch and Oromí, 2006). Frisch wrote that he regards species of Micranops to be inhabitants of humid, sandy soil on riverbanks and creeks with sparse vegetation, that the species live in the interstices of soil, and exhibit adaptations to an endogean mode of life ( Frisch and Herman, 2014: 68). Micranops myrmecophilus was collected in Argentina with Acromyrmex lundii Guérin-Méneville, 1838 , ( Bernhauer, 1921: 103) and M. pilicornis was collected from the nest of Messor concolor Santschi, 1927 , in Turkey ( Frisch, 1997c: 100). It seems highly improbable that either M. myrmecophilus or M. pilicornis are myrmecophiles. No scopaeine species are known to live with ants. The preceding records likely merely reflect that these species, like many other paederines, were simply collected from habitats that also included ants. Only further collecting and observation will resolve the question. If the specimens were collected with a sifter, little can be deduced about their true habitat. The few specimens I collected in Panama and Argentina were sifted from leaf litter near a stream and one within the entrance of a mammal burrow. (Note: The names of both species of ants above were corrected by consulting a pdf of Bolton’s, 2016, online General Catalogue to the Ants of the World. 1) Acromyrmex

1 Bolton, B. 2016. The general catalogue of the ants of the world. Word files of Barry Bolton, 3 May 2016. For taxonomic reference purposes. This is not a publication. Online resource (www.antwiki.org/wiki/images/d/dd/NGC_January_2016.pdf). (Using this address in a browser does not take one directly to the catalog, nor does going directly to www.antwiki.org make the catalog easy to find. Finding it is a bit of a scramble.) lundii was corrected from A. lundi and M. concolor is a junior synonym of Messor wasmanni Krausse, 1910 .)

SYNONYMY: Nivorus was described as a subgenus of Orus ( Herman, 1965a: 119) . Both Nivorus and Micranops share the short, deep, trichobothrial cavity on the lateral side of the head; no known characters distinguish the two generic groups. The type species of Micranops , M. brunneus (fig. 256), which I first saw in London in 1983 and recognized that it and species of Nivorus were congeneric, has reduced eyes, elytra, humeral angles, metathorax, and flying wings and is much larger; these reductions and size differential are insufficient reasons to recognize two genera. The type locality of M. brunneus is the Newcastle District at 3000 feet elevation, Jamaica.

Microscopaeus, described by Coiffait (1981: 19) as a subgenus of Scopaeus , was distinguished by the presence of an oblong pit, “fossette,” behind the eye (fig. 282). Although the localities cited in the original description of Scopaeus microphthalmus , the type species of Microscopaeu s, included various sites of the Levant, Frisch’s (1997c: 96) lectotype designation fixed the type locality as Crete.

In correspondence with Frisch, I suggested the Eastern and Western Hemisphere species with the postocular trichobothrial cavity were congeneric. He published that synonymy ( Frisch et al., 2002a: 46; 2002b: 1), but in correspondence a few years later professed misgivings about the synonymy. Only recently have SEM images of the trichobothrial cavity (figs. 266–268, 282, 283) revealed small differences of the position of the cavity relative to the eye and interesting structural variations of some details of the trichobothrial cavity between the New and Old World groups. Furthermore, the specimen from Burkina Faso has sensilla on some corneal lenses (fig. 19), that from Bimini does not (fig. 18). Both the eye and trichobothrial variations require detailed scrutiny of more specimens and species of both hemispheres.

The width of the neck compared with the width of the head differs between the groups of the two hemispheres, but that difference overlaps within one standard deviation (table 3). See the Discussion for further information on the overlap of the relative width of the head and neck.

Few species of both regions were available for study in the present work so the question could not be fully addressed here. Additional discussion of variation between the species of the two hemispheres follows below in the Discussion. The synonym of the two groups requires further study with, but more specimens and a larger sampling to the species of both regions.

FLIGHT AND SIGHT: “As far as known presently, most species of Micranops are able to fly” ( Frisch and Oromí, 2006: 35). Many species of the genus have normally developed eyes, elytra, metathorax, and wings. Some have reduced eyes and wings.

The first eyeless species was Micranops bifossicapitatus (Outerelo and Oromí, 1987) from the Canary Islands. Two decades later Frisch and Oromí (2006) described three more eyeless species, M. subterraneus , M. mlejneki , and M. spelaeus , from the Canaries. To date these four are the only known eyeless species of Micranops . As is typical for eyeless species, all of them also have reduced elytra with broadly rounded elytral humeral angles, reduced metathorax and wings, and lack a palisade fringe on tergite VII.

Micranops brunneus was the first species of the genus reported to be eyeless. In the original description Cameron (1913: 350) wrote that eyes were “absent, their position marked by a round whitish depression,” but he erred. I examined the holotype in London in 1983 and again in 2007. The eye of M. brunneus is a single, small, white corneal lens with a smooth, shiny surface. In line with the diminished eyes, the elytra are reduced, and the elytral humeral angle is broadly rounded, the metathorax and wings are reduced, and the palisade fringe of tergite VII is absent. I have examined four unnamed species from Australia, Malaysia, Costa Rica, and Peru with small or tiny eyes comprised of a few corneal facets and similarly reduced elytra, wings, metathorax, and without a palisade fringe.

Some of the corneal lenses of a specimen from Burkina Faso have sensilla (fig. 19). The sensilla are well developed and clustered on the posterodorsal two or three rows of lenses (fig. 282). A few lenses ventrad of those have poorly developed sensilla that may not be functional. The corneal lenses of an undescribed species from Bimini lack those sensilla, but the surface has some tiny bumps and ridges (fig. 18) that may be precursors, remnants of sensilla, or represent something different. Distribution of these sensilla among species of the genus requires further investigation. Of significant interest would be the geographical and taxonomic distribution of these ocular sensilla. Their function is unknown.

At least one species displays wing-dimorphic populations with both flying and flightless individuals. Frisch (in litt.: 2018 October 24, November 7) wrote that most of the dozens of specimens of M. pilicornis he collected in Anatolia are wingless, but that some have longer elytra with well-developed humeral angles and that at least one of them had fully developed wings exposed. He also stated that for flying specimens the palisade fringe is present and that the fringe is poorly developed or absent on flightless ones. Earlier he and his coauthor reported a flying specimen of the species had been collected in Italy and that the species is microphthalmic ( Frisch and Oromí, 2006: 35). I have seen only one specimen of the species ; the elytra appeared to be fully developed and the eyes are well developed.

For another species I examined just over 100 specimens from 10 localities of an unnamed North American species nearly all of which have reduced elytra, but for which the eyes appear normal, albeit slightly smaller, with numerous facets, than those of some congeners. The elytra and metathorax of all the males (40 specimens) were reduced and the wings were mere small pads ; the palisade fringe of tergite VII was present. Nearly all the 64 females of this North American species had similarly reduced wings ; nine females had what appeared to be fully developed elytra and metathorax and I assume fully developed wings. The winged females were all from localities from which I had no males, so the conspecificity of the winged and wingreduced specimens is uncertain as is the dimorphism of the species. However, the presence of a palisade fringe of tergite VII suggests there are flying individuals of the species. Certainly, there are other species with both flying and flightless populations .

DISCUSSION: Micranops was based on one specimen of M. brunneus , found in the Jamaican highlands at about 900 meters that, according to the author ( Cameron, 1913: 350), lacked eyes and was apterous. Blackwelder (1939a: 98), who studied no specimens of Micranops , but based on the original description used the absence of eyes to identify this genus in his key. However, the one known specimen has one white, corneal lens remaining; the eye may be nonfunctional or perhaps only light sensitive. In Blackwelder’s monograph of the West Indian Staphylinidae (1943) Micranops was neither addressed nor even mentioned. The genus remained effectively unknown until the works of Frisch and his coauthors (Frisch et. al, 2002a, 2002b; Frisch and Oromí, 2006; Frisch and Herman, 2014).

Herman (1965a: 119), unaware of the existence of Micranops , described Nivorus , type species Orus cameroni , as a subgenus of Orus , based on the presence of a furrow with a long “seta,” or as we now know, the sensory seta or trichoid sensillum of a trichobothrium, on the lateral side of the head. Two Caribbean species described by Blackwelder (1943: 277, 278) in Orus (Leucorus) , were the initial species included in Orus (Nivorus) ; a Surinamese species was added later ( Herman, 1965a, 1968b).

Coiffait (1952: 6) described Stilpon with three species ( S. baudrimonti , S. bordei [= S. portai ], and S. microphthalmus ), as a subgenus of Scopaeus with reduced eyes. The designated type species, Scopaeus baudrimonti , a junior synonym of Scopaeus ryei Wollaston, 1872 ( Frisch, 1998: 101) , has a supraocular trichobothrium, as does S. portai ; both species belong in Scopaeus . Later Coiffait (1960: 284) proposed Geoscopaeus to replace Stilpon , a junior homonym of Loew, 1859, and elevated the group to generic level, but incorrectly cited Scopaeus microphthalmus , which has a postocular trichobothrium, as type species of Geoscopaeus . Fagel (1973: 14, 18), in a monograph on African Scopaeus , continued to treat Geoscopaeus at the generic level, corrected the type species, but characterized the genus as having a large, cephalic, postocular pore with a long seta (= trichobothrium) on the temple. Fagel (1973: 21–36) then included 12 African species in Geoscopaeus , all with a postocular trichobothrium; later all were transferred to Micranops ( Frisch and Herman, 2014) . In his introductory remarks for Geoscopaeus, Fagel (1973: 18) indicated that along with the three species originally included by Coiffait (1952: 6), two Asian ( Scopaeus pallidulus Kraatz, 1859 , and Scopaeus planiusculus Kraatz, 1859 ) and one New World ( Scopaeus umbra Sharp, 1886 ) species should be added. However, although Fagel characterized the genus as possessing a setate postocular pore (= trichobothrium) only three ( S. microphthalmus , S. pallidulus , and S. planiusculus ) of the six included non-African species have postocular trichobothria; the trichobothrium of the others, including the type species of Geoscopaeus , is supraocular. It is unclear what specimens he examined for his assignments. The trichobothrium of the holotype of S. umbra is supraocular, so it remains in Scopaeus . All the specimens (that I’ve seen) subsequently identified as S. umbra in the Field (FMNH) and British (BMNH) Museums have a postocular trichobothrium and represent an unidentified species of Micranops .

Coiffait (1981: 19) removed G. microphthalmus Eppelsheim from Geoscopaeus and made it the type species of Microscopaeus, a new subgenus of Scopaeus that included one other species, S. yemenicus . This subgenus was defined by the presence of an oblong pit behind the eye. Finally, Coiffait (1984: 148) cited Geoscopaeus as a junior synonym of Scopaeus and continued to list Microscopaeus as a subgenus.

The type localities of Micranops and Microscopaeus, Jamaica and Crete respectively (see Synonymy above for details), are of note to the following two paragraphs concerning variation of the New and Old World species of the genus.

The neck of most Old World species of Micranops is narrow, but there is a wide range of variation that overlaps the wider neck of the New World species (table 3). In the Old World the ratio ranges from 0.18 to 0.40 (mean: 0.25; sample: 49; standard deviation: +/-0.05) and in the New World 0.28 to 0.40. (mean: 0.32; sample: 63; standard deviation: +/-0.03). As shown in table 3 the range of variation of the species of the two hemispheres overlaps at one standard deviation. The mean ratio of the neck width to head width of the Old World species is about one quarter and about one third for the New World species. However, the range of variation of this metric encompasses the entire range in the Old World species, from about one fifth to two fifths the width of the head. For the New World species, the neck ranges from about a quarter to two fifths the width of the head; there are no known specimens with a very narrow neck. In the Old World species with the narrower necks are nearly all Asian, while most of the African species have the wider neck found in the Americas. As can be seen in table 3, there are specimens that link the clusters of narrowneck and wide-neck species.

The surface of the head and pronotum of most species, both New World and Old, have dense microsculpturing that dominates the punctation and is best viewed with diffused light. The punctation of the head and pronotum of M. brunneus , the type species of Micranops , is distinct and clearly visible and the microsculpturing is strong and well developed. I have examined a species from Australia and another from Malaysia in which the distribution of the microsculpturing is restricted, portions of the integument are polished, and the punctation is strongly developed and clearly visible. The illustration of M. bifossicapitatus appears to show—and is confirmed in the description—clearly visible cephalic and pronotal punctation ( Frisch and Oromí, 2006: 27).

Frisch and Herman (2014) transferred 21 species to Micranops from Scopaeus and Lathrobium thereby making Micranops a moderately speciose genus with 33 described species. The authors included bibliographic references and a summary of the distribution for each species. However, the genus is far more widely distributed and speciose than their checklist indicated. Both authors have examined a significant number of undescribed species throughout the range of the genus. It is probable that many more of these tiny