Hygrogeus aemulus ( Rosenhauer, 1847 )

Shavrin, Alexey V., 2024, Review of Hygrogeus Mulsant & Rey, 1880 and Trichodromeus Luze, 1903, with descriptions of three new genera from the eastern Palaearctic Region (Coleoptera: Staphylinidae: Anthophagini: Omaliinae), Zootaxa 5531 (1), pp. 1-62 : 9-15

Hygrogeus aemulus ( Rosenhauer, 1847)

( Figs 1 , 7–27 )

Anthophagus aemulus Rosenhauer, 1847: 12 ; Kraatz 1857: 929, Fauvel 1865a: 316 [= 1865b: 66], 1871: 139 [=1872: 113], Portevin 1929: 433.

Geodromicus aemulus : Redtenbacher 1874: 266,

Geodromicus (Hygrogeus) aemulus : Mulsant & Rey 1880: 61.

Hygrogeus aemulus : Ganglbauer 1895: 710, Luze 1902: 529, Lohse 1964: 63, Zanetti 1987: 384, 2012: 68.

Anthophagus cenisius Fairmaire, 1862: 647 ; Fauvel 1865a: 316 [= 1865b: 66].

Other references see in Herman (2001).

Material examined. SWITZERLAND: 1 ♂: ‘ Gadmen 1887.VII.6 ’ ( MMBC) ; 1 ♀: ‘6.VII.87 Gadmen’ ( HNHM) ; 3 ♂♂, 3 ♀♀: ‘ Vals, Rhaetia Joerger 1938’ ( NHMB) ; 1 ♂: ‘ Helvetia: Zermatt, Gorner Grat, 14/ VI Dudich [?] leg.’ ( NMPC) ; 1 ♂, 1 ♀: ‘ Helvetia Sudeten’ ( HNHM) ; 1 ♀: ‘ Helvetia’ ( HNHM) ; AUSTRIA: 1 ♂, 1 ♀: ‘ Axams, Tirol leg. Knabl’ ( MMBC) ; 2 ♂♂, 1 ♀: ‘ Tirol’ ( NMPC) ; ITALY: 1 ♂: ‘ Monte Viso Bandi [?]’ ( HNHM) .

Remarks. Habitus as in Fig. 1 . Ventral view of the head as in Fig. 12 . Prothorax as in Fig. 13 . Mesoventrite as in Fig. 14 . Scutellum as in Fig. 17 . Metaventrite as in Fig. 15 . Metendosternite as in Fig. 16 . Elytron as in Fig. 18 . Labrum as in Fig. 7 . Mandibles as in Fig. 8 . Labium as in Fig. 10 . Mentum as in Fig. 11 . Maxilla as in Fig. 9 . Male abdominal tergite VIII as in Fig. 22 and sternite VIII as in Fig. 23 ; genital segment as in Fig. 24 . Female abdominal tergite as in Fig. 25 and sternite VIII as in Fig. 26 ; genital segment as in Fig. 27 .

Hygrogeus aemulus was redescribed several times (see above) and recorded many times from the Alps ( Horion

1963; Herman 2001, etc.).

“ Hygrogeus ” minor Coiffait, 1983

Hygrogeus minor Coiffait, 1983: 285 ; Herman 2001: 309, Smetana 2004: 245, Schülke & Smetana 2015: 316.

Remarks. Hygrogeus minor was described based on a female from “Cachemire, Rohtang Pass, 4000 m …”. Based on the shorthened antennomeres, the transverse pronotum, and short elytra this small (4.0 mm) species is not conspecific with Hygrogeus aemulus . Regarding the morphological features provided in the original description, it may be Trichodromeus or Microedus , some small species of which have shortened antennomeres ( Shavrin 2023, 2024a). It is necessary to study the holotype to clarify the taxonomic status of this species.

“ Hygrogeus ” rugosicollis Coiffait, 1983

Hygrogeus minor Coiffait, 1983: 284 ; Herman 2001: 309; Smetana 2004: 245; Schülke & Smetana 2015: 316.

Remarks. Hygrogeus rugosicollis was described based on a female from “Cachemire, Badrinath, 3500 m …”. As well as the previous taxon, this small (4.50 mm) species is not conspecific with H. aemulus and can be attributed to Trichodromeus or Microedus .

Genus Trichodromeus Luze, 1903

( Figs 2–6 , 28–65 )

Type species: Hygrogeus penicillatus Reitter, 1900 , fixed by subsequent designation by Blackwelder (1952).

Trichodromeus Luze, 1903: 116 (subgenus of Geodromicus ); Bernhauer & Schubert 1910: 75, Tichomirova 1973: 141. Trichodromeus (valid genus): Bordoni 1990: 100, Zerche 1992: 126, 134.

Neogeodromicus Bordoni, 1985: 373 .

Redescription. Body small to large (3.7–8.6 mm), convex. Coloration yellow-brown to black. Punctation of forebody variable, but usually dense and moderately large, denser and larger on pronotum and elytra; abdomen with fine and dense punctation. Body glossy; head and pronotum with dense and sometimes coarse microsculpture; abdomen with fine microreticulation. Pubescence of forebody dense, moderately long, semierect, longer in apical portion of head; abdomen with dense, decumbent pubescence, slightly finer than that on forebody.

Head transverse, with strongly elevated narrow or moderately wide supra-antennal prominences, with distinctly elevated middle and infraorbital portions; anteriomedian depression wide and deep, sometimes connected with interocellar depression; interocellar depression narrow, subrectangular or moderately wide and subtrapezoidal; anteocellar foveae variable, indistinct or distinct, long, slightly or strongly divergent latero-anteriad or shortened and slightly longer than diameter of ocellus. Temples convex, variable in length, shorter or slightly longer than longitudinal length of eyes. Eyes moderately small or large, convex. Ocelli small (sometimes indistinct) or large, but some species with completely reduced ocelli (e.g. T. schmidti Zerche, 1992 ). Gular sutures narrowly separated at level of posterior margins of eyes, gradually divergent posteriorly towards base of head ( Fig. 32 ). Labrum strongly transverse, with slightly ( Fig. 1E in Cheng & Peng (2019)) or strongly protruded anteriad widely rounded latero-apical portions ( Fig. 28 ), with widely concave apical margin and elongate laterobasal projections. Mandibles with wide basal part, apical part with narrow, elongate and strongly curved acute apex; inner margins of each mandible with three distinct teeth: two longer triangular preapical teeth and small basal tooth, with wide truncate apex in left and triangular in right mandible ( Fig. 29 ). Mentum small, transverse ( Fig. 31 ). Labium narrow, with elongate labial palpomeres; preapical palpomere about as long as or slightly shorter than preceding segment; apical palpomere about twice longer than preapical segment; glossa relatively narrow and elongate ( Fig. 31 ). Maxilla with relatively elongate maxillary palpomeres 2–4, with penultimate segment distinctly broadened apicad, covered with dense pubescence; last (apical) maxillary palpomere slightly narrower and about as long as or slightly longer than preapical segment, from widest basal part or middle gradually narrowed toward truncate or rounded apex; galea narrow, disinctly longer than lacinia; lacinia narrow, with narrow curved apex and several elongate teeth along medial margin ( Fig. 30 ). Antenna variable in length, reaching basal third or apical third of elytra, with elongate or distinctly shortened (e.g. T. pusillus , Fig. 42 ) antennomeres; basal antennomere broadened, about three times as long as broad or slightly shorter.

Pronotum slightly or strongly transverse, subtrapezoidal, widest in anterior portion, slightly or strongly narrowed posteriad, with anterior angles and medioapical portion not or distinctly protruded anteriad; middle portion without or with distinct longitudinal depression; lateral portions narrowly bordered and slightly impressed, with wide, shallow or deep laterobasal depressions. Prothorax with narrow prosternum, moderately short elongate intercoxal process; pronotal epipleura moderately broad; prosternal processes relatively narrow, with rounded apices ( Fig. 33 ). Mesoventrite strongly transverse, with very deep and wide apical emargination, with relatively short and narrow intercoxal process not reaching apices of middle of mesocoxae ( Fig. 34 ). Scutellum moderately large, transverse, with wide apical part, rounded apically ( Fig. 37 ). Metaventrite transverse, moderately narrow, with deep and wide interocoxal cavities and narrow elongate intercoxal process ( Fig. 35 ). Metendosternite as in Fig. 36 .

Elytra variable in shape, usually wide and long, slightly less than twice or longer than pronotum and reaching apical margins of abdominal tergites III to V, with narrow elytral epipleurae ( Fig. 38 ); some species with short elytra (e.g. T. abbreviatus ). Hind wings fully developed or reduced to small vestiges ( T. abbreviatus , as in Fig. 1 in Shavrin (2023)).

Legs elongate, with tibiae slightly broadened toward apex, covered with dense and short setae, with additional strong spines in apical portions; males usually with slightly broadened femora and protarsomeres 1–4.

Abdomen narrower or broader than elytra, without or with two large transverse tomentose spots in the middle of abdominal tergite IV and with small oval spots in the middle of abdominal tergite V (invisible in some specimens), with narrow palisade fringe on apical margin of abdominal tergite VII.

Male. Aedeagus with wide or narrow median lobe, sometimes with sclerotized mediolateral and preapical elongate structures as in some Himalayan species ( Shavrin 2021); parameres narrow, shorter or longer than apex of median lobe, sometimes with additional lateral setation; internal sac complicated (some species with sclerotized elongate structures), with distinct fields of numerous spines and with very long flagellum spirally folded in basal portion, usually with broadened preapical part. Genital segment as in Fig. 61 .

Female. Gonocoxites narrow and elongate; stily short, narrow, each with long apical seta ( Fig. 64 ).

Natural History. Trichodromeus can be regarded as habitants of alluvial communities and can be found along banks of streams, rivers and lakes under stones and debris, and sometimes can be sifted from leaf litter, moss and other organic substrates in floodplain forest near rivers, under stones near snow fields in the alpine zone, etc. Species are known at elevations from 1500 to 4800 m a.s.l.

Distribution. Species of Trichodromeus are distributed in the eastern Palaearctic Region, and known from Middle Asia, the Himalayan Region and Tibet.

Remarks. Based on details of the sculpture of the head and the pronotum, the general shape of the transverse head with somewhat similar shape of the interocellar depression, the presence of the protruded apical part of the pronotum with distinct longitudinal depression on the pronotum (some species), and the general morphology of the aedeagus, Trichodromeus is somewhat similar to Himalodromeus gen. n. (see below). It can be distinguished from the latter genus by the following morphological features: 1) smaller body, 2) lack of bluish reflex on the elytra, 3) shorter maxillary palpomeres, with pubescence only on the preapical segment and distinctly shorter apical segment ( Fig. 30 ), 4) presence of an additional basal tooth with truncate apex on the inner margin of the mandible ( Fig. 29 ), 5) shorter apical labial palpomere ( Fig. 31 ), 6) broader and shorter basal antennomere, 7) narrower pronotum, with narrow pronotal epipleura and absence of the crenulation on the lateral margins ( Fig. 33 ), 8) shape of elytra less broadened posteriad ( Fig. 38 ), 9) different shape of posterior margin of male abdominal sternite VIII, 10) narrower aedeagus, with presence of long parameres. See also key to genera below.

Some species can vary in proportions of the pronotum and ground sculpture of the forebody (e.g. T. armatus ( Fig. 2–3 ), T. ketmeniensis ( Figs 4–5 )). However, the variability of the shape of the aedeagus is insignificant, with a few exceptions (e.g. T. ketmeniensis ( Figs 43, 45–46 )).

List of species

Figures

FIGURES 1–6. Habitus of Hygrogeus (Fig. 1) and Trichodromeus (Figs 2–6): 1—H. aemulus (Tirol), 2—T. armatus (Kashmir: Baltal), 3—T. armatus (Kashmir: Kolahoi Glacier), 4—T. ketmeniensis (Kyrgyzstan: Chatkal Mts.), 5—T. ovchinnikovi (holotype), 6—T. kumaonensis (paratype). Scale bar: 1.0 mm.

FIGURES 7–18. Hygrogeus aemulus: 7—labrum (dorsal view), 8—mandibles (left and right, dorsal view), 9—maxilla (dorsal view), 10—labium (ventral view), 11—mentum (ventral view), 12—head (ventral view), 13—prothorax (ventral view), 14— mesoventrite (ventral view), 15—metaventrite (ventral view), 16—metendosternite (dorsal view), 17—scutellum (ventral view), 18—elytron (ventral view). Scale bar: 0.1 mm.

FIGURES 19–27. Hygrogeus aemulus: 19, 21—aedeagus, parameral view, 20—aedeagus, lateral view, 22—male tergite VIII, 23—male sternite VIII, 24—male genital segment, 25—female tergite VIII, 26—female sternite VIII, 27—female genital segment. Scale bar: 0.1 mm.

FIGURES 28–38. Trichodromeus penicillatus: 28—labrum (dorsal view), 29—mandibles (left and right, dorsal view), 30—maxilla (dorsal view), 31—labium and mentum (ventral view), 32—head (ventral view), 33—prothorax (ventral view), 34—mesoventrite (ventral view), 35—metaventrite (ventral view), 36—metendosternite (dorsal view), 37—scutellum (ventral view), 38—elytron (ventral view). Scale bar: 0.1 mm.

FIGURES 39–46. Aedeagus of Trichodromeus (Figs 39–40: T. armatus (Kashmir: Kolahoi Glacier), Figs 41–42: T. jaegeri (Nepal: Gandaki), Figs 43–46: T. ketmeniensis (Figs 43–44: Kazakhstan, Kulbastau), Fig. 45: Kyrgyzstan, Sary-Chelek, Fig. 46: Kazakhstan, Dolaity): 39, 42, 43, 45–46—parameral view, 40, 42, 44—lateral view. Scale bar: 0.1 mm.

FIGURE 47. Distribution of Trichodromeus jaegeri Shavrin, 2021 (circles) and T. telnovi sp. n. (square) in Nepal.

FIGURE 48. Distribution of Trichodromeus ketmeniensis Bordoni, 1985 in the Middle Asia (black circles: specimens studied by the author; white circles: previously published records, specimens not see nby the author).

FIGURES 49–51. Habitus of Trichodromeus: 49—T. penicillatus (Kazakhstan: Aksu-Dzhabagly), 50—T. pusillus (Kashmir), 51—T. telnovi (holotype). Scale bar: 1.0 mm.

FIGURES 52–58. Aedeagus of Trichodromeus (Figs 52–53: T. kumaonensis (paratype), Figs 54–55: T. telnovi (holotype), Figs 56–58: T. penicillatus (Figs 56–57: Kazakhstan, Dzhabagly; Fig. 58: Kyrgyzstan, Chakmak): 52, 54, 56, 58—parameral view, 53, 55, 57—lateral view. Scale bar: 0.1 mm.

FIGURES 59–64. Abdominal segments (ventral view) of Trichodromeus penicillatus: 59—male tergite VIII, 60—male sternite VIII, 61—male genital segment, 62—female tergite VIII, 63—female sternite VIII, 64—female genital segment. Scale bar: 0.1 mm.

FIGURE 65. Distribution of Trichodromeus penicillatus (Reitter, 1900) in Middle Asia. Black circles: material studied by author, white circles: previously published material not seen by author.