Microedus LeConte, 1874

Shavrin, Alexey V., 2024, Microedus LeConte, 1874 (Coleoptera: Staphylindae: Omaliinae: Anthophagini), a new genus for the Palaearctic Region, Zootaxa 5443 (2), pp. 205-223 : 207-209

Genus Microedus LeConte, 1874

(type species: M. austinianus LeConte, 1874 , fixed by monotypy)

( Figs 1–29 , 31–42 )

Microedus LeConte, 1874: 273 ; Fauvel 1878a: 250 [= 1878b: 86], Hatch 1957: 51, Moore 1966: 48, Moore & Legner 1972: 75, 1975: 184, Downie & Arnett 1996: 1996: 435, Newton et al. 2000: 340

Lioplax Nakane & K. Sawada, 1956: 183

Liophilydrodes Nakane, 1983: 148 syn. n.; Watanabe 1990: 295

Altaiodromicus Zerche, 1992: 107 syn. n.

For other references see Herman (2001).

Redescription. Head, pronotum and abdomen slightly convex; elytra flattened, slightly or strongly broadened posteriad. Body shiny, with dense coriaceous microsculpture on head and pronotum or without it ( M. puncticollis ); sometimes elytra subrugosely sculptured ( M. rogersi ); body length varying from 2.60 to 5.50 mm. Coloration brown to reddish-brown or black. Head and pronotum with fine and moderately dense punctation; punctation of elytra distinctly denser, larger and deeper than that on pronotum; abdomen with distinct, regular, dense and fine punctation.

Head subtrapezoidal, with postocular parts usually widened and relatively long, with distinctly elevated part between bases of antennae and infraorbital portions; supra-antennal protuberances narrow, distinctly elevated, diagonally stretching from base of antennae to about level of apical margins of eyes; medioapical depression deep and wide, slightly or strongly narrowing posteriad toward level of anterior margins of eyes; interocellar depression shallow or well-distinct and moderately deep; anteocellar furrows (grooves in front of ocelli) narrow or very deep and moderately wide, diagonally stretching anteriad toward level of anterior third of eyes. Eyes relatively small, convex. Ocelli convex, small, but well visible. Labrum transverse, with slightly and widely concave apical margin and slightly elongate basolateral projections, with several very long setae in latero-apical and middle portions ( Figs 6–7 , and Fig. 398 in Watanabe (1990)). Mandibles with wide basal part and elongate, strongly curved apical portion; inner margin of each mandible with two elongate teeth ( Figs 8–9 , and Fig. 396 in Watanabe (1990)). Maxillae relatively wide, with elongate galea and maxillary palpomeres; apical maxillary palpomere somewhat elongate, narrow, distinctly more than twice narrower than markedly widened preceding segment; lacinia moderately short, with several elongate preapical teeth ( Figs 10–11 ). Labium narrow; labial palpomere 2 about as long as broad, preapical palpomere distinctly longer than broad, apical palpomere narrow, distinctly longer than preceding segment ( Figs 12–13 and Fig. 399 in Watanabe (1990)); labial palpomere 2 slightly elongate ( Fig. 12 ) or transverse ( Fig. 13 ). Mentum narrow, transverse, as in Fig. 399 in Watanabe (1990). Gular sutures narrowly (see Fig. 400 in Watanabe (1990)) or relatively widely separated from each other at level of posterior margins of eyes, strongly divergent posteriad. Antennae long, exceeding middle or apical third length of elytra when reclined, with antennomeres 4–10 slightly or distinctly elongate.

Pronotum convex, distinctly transverse, widest in anterior portion, not or distinctly protruding anteriad ( M. fenderi ), gradually or strongly narrowed posteriad, narrowly or widely bordered laterally and sometimes distinctly explanate and reflexed ( M. fenderi ); mediobasal portion sometimes with shallow transverse impression. Prothorax short, strongly transverse, distinctly convex in middle, with long and acute intercoxal process reaching about middle of front coxae. Mesoventrite moderately short, strongly convex, with acute elongate process, reaching apex of relatively long and narrow intercoxal process extending to about middle of mesocoxae. Scutellum large, triangular, without punctation. Metaventrite transverse, convex, with very deep intercoxal cavities and angular intercoxal process extending to mesosternal process.

Elytra wide, slightly or strongly broadened posteriad, with narrow or wide and distinctly reflexed ( M. fenderi ) lateral margins, elongate or moderately short, reaching apical margin of abdominal tergite III to V. Hind wings fully developed.

Legs relatively slender, moderately long, with transverse procoxae and metacoxae, and large suboval mesocoxae; protarsi of males with distinctly dilated protartsomeres 1–4; metatarsus more than twice shorter than metatibiae; apical antennomere slightly shorter than preceding four metatarsomeres.

Abdomen slightly or distinctly broader than elytra, with two oval or transverse tomentose spots in the middle of abdominal tergite IV; apical margin of abdominal tergite VII with narrow palisade fringe.

Aedeagus elongate or moderately short ( M. kastcheevi sp. n., M. schilenkovi ), with small or very large phallobase, gradually narrowed apicad; parameres narrow, reaching or exceeding apex of median lobe; internal sac narrow, without or with elongate and sclerotized structures, sometimes with flagellum.

Female genital segment with narrow and very long gonocoxites, with moderately short and narrow styli, each with long apical setae ( Figs 29 , 42 ).

Immature stages unknown.

Comparative notes. Based on the general shape of the body and the aedeagus, and the presence of an interocellar depression, the genus Microedus is related to genera of the Hygrogeus complex, distributed in the Holarctic Region ( Zerche 1992, Shavrin 2017). Regarding the general shape of the narrow apical segment of the maxillary palpi, the ground sculpture of the forebody, and the shape of the transverse pronotum, Microedus is similar to Hygrodromicus Tronquet, 1981 and Philydrodes Bernhauer, 1929 . It can be distinguished from Hygrodromicus by the narrower apical and somewhat broader preapical segments of the maxillary palpi, longer temples, and the general shape of the aedeagus (basal portion of aedeagus of Hygrodromicus usually small and rotated inside the abdomen in lateral position (90°), as in Philydrodes too). It can be distinguished from Philydrodes by the shape of the labrum, broader mandibles, the shorter and broader preapical and longer apical segments of the maxillary palpi, shorter temples, and the significantly broader pronotum. From all genera listed above and other genera of the Hygrogeus complex it can be distinguished by the external and internal morphology of the aedeagus. A more detailed analysis of relations of these genera within Hygrogeus complex will be published in detail in a forthcoming revision of the genus Trichodromeus Luze, 1903 and related genera of the Palaearctic Region (in prep.).

Distribution. Species of the genus Microedus are distributed in the Nearctic ( Canada, USA) and Palaearctic regions ( Russia (Altai, Russian Far East), Kazakhstan (Altai and Dzhungar mts.), India (Himalayas), and Japan (Hokkaido, Honshu).

Bionomics. Species of Microedus inhabit sand or gravel banks of rivers, streams and lakes, in moss and litter, and can be found frequently in the mountains ( Hatch 1957, Newton et al. 2000, present study).

Remarks. The genus Altaiodromicus was originally described based on a single species ( A. schilenkovi Zerche, 1992 ) from Altai Mts., Russia. Based on the shape of the body ( Fig. 4 ), it was compared with Hygrodromicus and Geodromicus Redtenbacher, 1857 and distinguished by the narrow apical maxillary palpomere and different morphology of the aedeagus. During the study of Omaliinae material collected by Dr. Kastcheev, I found a new, similar species from Kazakhstan. This new species can be clearly distinguished from A. schilenkovi by the presence of sclerotized elongate structures within the internal sac ( Fig. 22 ) and some other morphological features (see below). Besides that, I studied the holotype of Geodromicus brevitarsis Champion, 1925 from northern India ( Fig. 2 ). The apical maxillary palpomere of this species is also narrow, and based on the slightly elongate antennomeres 4–10, G. brevitarsis is somewhat similar to the two species listed above, but differs by the smaller and narrower body, with markedly narrower pronotum, and different morphology of the aedeagus. Based on the external morphological features, one unnamed species from Kashmir is also similar to G. brevitarsis (see below). Several years ago, with the assistance of the late A. Smetana, I received several Nearctic species of Microedus from Canada and USA. During the study of mouthparts and aedeagi of these species, I found that they are similar to species of Altaiodromicus ( Figs 6–13 ) and G. brevitarsis . The general shapes of the body ( Fig. 1 ) and the aedeagus ( Fig. 14 ) of the type species of Microedus ( M. austinianus ) are somewhat similar to these of M. brevitarsis ( Fig. 16 ). The shapes of antennomeres 4–10 of M. austinianus are also similar to these in all Asian species listed above. Other Nearctic species of Microedus studied by me ( M. fenderi Hatch, 1957 , M. laticollis ( Mannerheim, 1843) and M. porterae Hatch, 1957 ) have more elongate antennomeres 4–10. Besides that, all these species have similar ground sculpture of the forebody and shape of the female genital segment ( Fig. 29 ). Thus, I decided to synonymize the genus Altaiodromicus with Microedus and transfer G. brevitarsis to this genus.

Species of Liophilydrodes , known from Japan and Far Eastern Russia have a narrow apical segment of maxillary palpi, similar general shape of the body and mouthparts (see Figs 396–399 in Watanabe (1990)) as in species from Middle Asia and the Nearctic Region. All species of Liophilydrodes have elongate antennomeres 4–10. Some species have similar shapes of aedeagi as those from Middle Asia, with the presence of elongate structures within the internal sac ( Fig. 34 ), sometimes with flagellum as in Figs. 21–26 in Shavrin & Makarov (2019). Thus, the genus Liophilydrodes is synonymized with Microedus .

The Palaearctic species of Microedus vary in proportions of the antennomeres, the shape of the interocellar foveae, the pronotum and the aedeagus as in some other taxa of the Hygrogeus group (e.g. Shavrin (2022b)). Species of the Nearctic Region are in need of a comprehensive taxonomic revision due to significant morphological differences between species (e.g. M. fenderi ).

Figures

FIGURES 1–5. Habitus of Microedus: 1—M. austinianus (USA: New Hampshire), 2—M. brevitarsis (holotype), 3—M. kastcheevi (paratype, Kazakhstan: Dzhungar Mts.), 4—A. schilenkovi (Russia: Altai, Korgon Mts.), 5—M. sp. (Kashmir). Scale bar: 1.0 mm.

FIGURES 6–13. Mouthparts (dorsal view) of M. austinianus (Figs. 6, 8, 10, 12) and M. schilenkovi (Figs. 7, 9, 11, 13): 6–7— labrum, 8–9—mandibles (left and right), 10–11—maxilla (right), 12–13—labium. Scale bars 0.1 mm.

FIGURES 14–17. Aedeagus of Microedus austinianus (Figs 14–15: Canada, Quebec, Riviere-a-Claude) and M. brevitarsis (Figs. 16–17: holotype): 14, 16—parameral view, 15, 17—lateral view. Scale bar: 0.1 mm.

FIGURES 18–23. Aedeagus of Microedus schilenkovi (Figs 18–19: Russia, Altai, Aygulakskiy Mts.; Fig. 20: Russia, Altai, Teletskoye Lake; Fig. 21: Kazakhstan, Tauchilik River) and A. kastcheevi (Figs. 22–23: paratype, Dzhungar Mts.): 18, 20–22— parameral view, 19, 23—lateral view. Scale bar: 0.1 mm.

FIGURES 24–29. Abdominal segments of Microedus schilenkovi: 24—male tergite VIII, 25—male sternite VIII, 26—male genital segment, 27—female tergite VIII, 28—female sternite VIII, 29—female genital segment. Scale bars 0.1 m

FIGURES 31–33. Lectotype labels (Fig. 31–32) and habitus (Fig. 33) of Microedus subtilis: 31–32—lectotype, with type labels, 33—Japan: Honshu: Mt. Hotaka. Scale bar: 1.0 mm.

FIGURES 34–42. Aedeagus (Figs. 34–36: Japan: Honshu, Mt. Hotaka) and abdominal segments (Figs. 37–42) of Microedus subtilis: 34—aedeagus, parameral view, 35—aedeagus, apex of median lobe, 36—aedeagus, lateral view, 37—male tergite VIII, 38—male sternite VIII, 39—male genital segment, 40—female tergite VIII, 41—female sternite VIII, 42—female genital segment. Scale bars 0.1 mm.