Stenichnus

Jałoszyński, Paweł, 2013, Revision of subgenera of Stenichnus Thomson, with review of Australo-Pacific species (Coleoptera, Staphylinidae, Scydmaeninae), Zootaxa 3630 (1), pp. 39-79 : 41-50

Morphology of Stenichnus s. str.

General body shape ( Figs. 1–4 ) elongate, body distinctly constricted between head and pronotum and pronotum and elytra, moderately to strongly convex; appendages long and moderately slender, vestiture moderately long and dense and composed of thin setae, without thick bristles.

Head capsule ( Figs. 5–8 ) divided by occipital constriction ( Figs. 5, 7–8 ; occ) into large anterior and small posterior part ('neck region'), the posterior part retracted into pronotum. Neck region ( Figs. 7–8 ; nr) subcylindrical, broadest near middle and slightly narrowing towards foramen occipitale ( Figs. 7–8 ; fo); narrowest site of occipital constriction only slightly narrower than vertex. Anterior part of head ( Figs. 5, 7–8 ) approximately subtriangular, broadest at posteriorly located compound eyes ( Fig. 5 ; ce) and narrowing anteriorly. Dorsum of head ( Fig. 5 ) convex; tempora ( Figs. 5, 7 ; tm) much shorter than eyes; vertex ( Fig. 5 ; vt) transverse and nearly evenly convex, anteriorly confluent with subtrapezoidal and convex or flattened frons ( Fig. 5 ; fr), which is gradually (not steeply) declining anteriorly; supraantennal tubercles feebly developed, often barely marked; genae ( Fig. 7 ; gen) small. Clypeus ( Figs. 5–6 ; cp) separated from frons but not from genae by distinct but short transverse fronto-clypeal groove ( Figs. 5–6 ; fcg). Ventral side of head ( Fig. 8 ) flattened except for strongly convex neck region; gular plate ( Figs. 6–8 ; gp) subtrapezoidal, large, with rounded sides and distinct but fine gular sutures ( Figs. 6–8 ; gs), distinctly demarcated from submentum ( Fig. 8 ; smn) by deep groove; posterior tentorial pits located between gular plate and submentum, hidden in groove separating these structures.

Mouthparts ( Figs. 5–17 ). Labrum ( Figs. 5–6 , 9, 11 ; lb) transverse, with rounded sides slightly convergent anteriorly and nearly straight anterior margin with membranous marginal velum ( Fig. 9 ; mv), dorsal surface with two transverse rows of four long setae in each. Epipharynx (ventral surface of labrum) ( Figs. 10, 12 ; eph) with several anterior marginal seta-like sensilla ( Fig. 10 ; ms), lateral groups of sparsely distributed trichia ( Fig. 10 ; tr) directed antero-mesally and lateral groups of circular or oval glandular openings ( Fig 10 ; gl). Mandibles ( Figs. 5, 8 , 9, 11–13 ; md) symmetrical, falciform, long and slender, with broadened base but without setose prostheca, with moderately deep basal pouch ( Figs. 9, 11 ; bp) bearing two setae; basal part of mandible dorso-mesally with microsculpture composed of elongate cells ( Fig. 11 ), distal part of mandible with finely denticulate mesal margin ( Fig. 13 ). Maxillae ( Figs. 14, 16 ) elongate, with large subtriangular cardo ( Fig. 16 ; cd) bearing long sub-basal seta; basistipes ( Fig. 16 ; bst) triangular, with one long basal and one long sub-basal lateral seta; mesostipes ( Fig. 16 ; mst) elongate and broad, with three short median setae; palpifer ( Fig. 16 ; ppf) elongate, with one long lateral sub-apical seta; galea ( Figs. 14, 16 ; gal) elongate and slender, with long and dense trichia along distal margin and four long setae on external margin; lacinia ( Figs. 14, 16 ; lac) elongate, with long and dense trichia along distal and mesal margins; maxillary palps ( Figs. 14–15 ) long, palpomere I ( Fig. 14 ; mxp1) small, as long as broad or only slightly longer and asetose, palpomere II ( Fig. 14 ; mxp2) elongate and strongly thickening distally, with sparse setae, palpomere III ( Fig. 15 ; mxp3) slightly longer than II and pedunculate, broadest near middle, nearly cylindrical in distal half, covered with sparse and long setae; palpomere IV ( Fig. 15 ; mxp4) small, subconical, with elongate and pointed apical part, with dense and moderately long setae near base and asetose in distal third. Labium ( Figs. 8 , 16–17 ) with elongate, trapezoidal submentum ( Fig. 8 ; smn) laterally separated from hypostomae ( Fig. 8 ; h) by lateral sutures ( Fig. 8 ; lss) and bearing a pair of long latero-anterior setae; mentum ( Figs. 8 , 16 ; mn) subtrapezoidal with one pair of long and one short latero-anterior setae; prementum ( Figs. 8 , 16 ; pmn) relatively long and flexible, with a pair of oval labial discs ( Fig. 17 ; ld); labial palps slightly shorter than mentum, with broadly separated bases, palpomere I ( Figs. 16–17 ; lp1) about as long as broad, asetose, palpomere II ( Figs. 16–17 ; lp2) strongly elongate and slightly broadening distally, with two sub-median and sub-apical setae, palpomere III ( Figs. 16–17 ; lp3) long and slender, asetose, with blunt apex. Hypopharynx (dorsal surface of labium) ( Fig. 14 ; hph) with elongate lateral lobes ( Fig. 14 ; llh) densely covered with microtrichia. Posteriorly and laterally mouthparts demarcated by hypostomal ridges ( Fig. 8 ; hr) strongly convergent caudad; hypostomae ( Fig. 8 ; h) subtriangular and elongate.

Antennae ( Figs. 1–4 , 7 ) slender, gradually thickening towards apices, antennomeres moderately compactly assembled, sparsely covered with suberect to erect setae.

Prothorax ( Figs. 18–21 ) moderately convex, in dorsal view ( Fig. 18 ) approximately pentagonal with rounded anterior part, without anterior corners, without lateral marginal carinae or sharp edges, posterior corners of pronotum blunt but well-defined. Pronotum ( Figs. 18, 20 ; pn) with two pairs of small and shallow lateral ante-basal foveae ( Figs. 18–19 ; bf), in some species foveae may be accompanied or replaced by a transverse row of small punctures. Prosternum ( Fig. 21 ) about 3–4 times shorter than pronotum, with basisternal part ( Fig. 21 ; bs) short and demarcated from procoxal cavities ( Fig. 21 ; pcc) by distinct carina; procoxal cavities separated in middle by fine median prosternal intercoxal carina ( Fig. 21 ; psc); procoxal sockets ( Fig. 21 ; pcs) closed by lateral expansions of prosternum; profurcal foveae ( Fig. 21 ; pff) relatively small. Hypomera ( Fig. 21 ; hy) subtriangular, elongate, expanded mesally, not demarcated from pronotum, demarcated from sternum by notosternal sutures ( Fig. 21 ; nss).

Mesothorax ( Figs. 22–30 ). Mesonotum ( Fig. 22 ) subtriangular in shape; mesoscutum ( Fig. 22 ; sc2) strongly transverse, with lateral groups of setae; scuto-scutellar suture ( Fig. 22 ; sss) present and distinct; mesoscutellum ( Fig. 22 ; scl2) well-visible between bases of elytra in intact specimens, subtriangular with concave sides and rounded posterior margin; anterior and posterior notal processes ( Fig. 22 ; anp, pnp) prominent.

Mesoventrite ( Figs. 23–26 , 29–30 ) relatively short, much broader than long, with narrow anterior ridge ( Figs. 23, 26 ; ar) bearing small subtriangular median projection not connected to mesoventral intercoxal process; mesoventrite behind anterior ridge with a pair of lateral asetose impressions ( Figs. 23, 26 , 29 ; ai) separated in middle and with large setose impressions ( Figs. 23, 26 , 29 ; si) narrowly separated in middle and narrowly separated from mesocoxal cavities; mesoventral intercoxal process ( Figs. 23, 26 , 29–30 ; msvp) narrow and moderately strongly projecting ventrally, posteriorly separated from metaventrite; mesocoxal cavities ( Figs. 23, 26 , 29 ; mscc) asetose, with anterior marginal carina ( Figs. 23–24 ; amc), its lateral parts extending into mesocoxal projections ( Figs. 23 , 29 ; mcp), posterior margin of mesocoxal cavities with dense setae. Each mesocoxal projection with subtriangular posterior lobe ( Figs. 24–26 ; pl) concealed by dense setae and best visible in transparent slide preparations; mesocoxal sockets ( Figs. 23, 26 ; mscs) located laterally; mesofurcal foveae ( Figs. 23, 26 ; msff) small and located sub-medially on lateral parts of mesocoxal cavities. Prepectus ( Figs. 23, 26 , 29–30 ; pre) very long and distinctly demarcated from mesocoxal projection and from posterior part of mesanepisternum ( Figs. 23 , 29–30 ; aest2), which is partly visible in ventral view and completely demarcated from mesepimeron; mesepimeron ( Fig. 30 ; epm2) elongate and concave.

Metathorax ( Figs. 27–30 ). Premetascutum ( Figs. 27–28 ; prsc3) large, transverse; metascutum ( Figs. 27–28 ; sc3) very large and transverse, with robust oblique lateral apodemes ( Fig. 28 ; ap) on ventral side, in middle with broad and impressed median membranous area ( Figs. 27–28 ; mma); alacristae ( Figs. 27–28 ; alc) nearly as long as scutum; metascutellum indiscernible, metascuto-scutellar suture indiscernible; metapostnotum ( Figs. 27–28 ; psn3) large, strongly transverse.

Metaventrite ( Figs. 29–30 ; v3) much longer than mesoventrite, broader than long, anteriorly fused with mesoventrite, with distinct metaventral anterior process ( Figs. 29–30 ; mtap), lateral margins slightly rounded, lateral (admetacoxal) parts of posterior margin weakly concave, in middle posterior margin expanded caudad and forming broad and short subtrapezoidal metaventral intercoxal process ( Fig. 29 ; mtvp) with distinct median notch. Metanepisternum ( Figs. 29–30 ; aest3) partly visible in ventral view, strongly elongate and narrow, slightly narrowing caudad; metepimeron ( Fig. 30 ; epm3) elongate, with dorsal sclerite distinctly broadening caudad.

Metafurca (metendosternite) ( Fig. 31 ) with short stem ( Fig. 31 ; mtfs) and strongly divergent lateral furcal arms ( Fig. 31 ; mtfa) expanded at apices.

Elytra ( Figs. 1–4 , 27 ) oval, with rounded apices; humeri without denticle and with variously large, but distinct humeral callus; sub-humeral lines or carinae absent; elytral base with one moderately large, deep circular and asetose basal fovea ( Fig. 27 ; bef) and visible only in transparent mounts trace of another fovea located close to humerus. Metathoracic wings (not shown) about twice as long as elytra, with posterior margin bearing dense fringe of long setae; venation highly reduced and homology of few indistinct veins visible only in basal part of wing difficult to interpret. Legs ( Figs. 1–4 ) moderately long and slender, without special characters except for modifications in males of some species: profemora with angulate or rounded dorsal expansion, in some cases strongly flattened laterally; and (less frequently) metatibiae with a denticle or tooth-like projection.

Abdomen ( Figs. 32–33 ) elongate, abdominal sternites III–VIII ( Fig. 32 ; st3–8) gradually narrowing towards abdominal apex, sternite VIII longest; suture between sternite VII and VIII ( Fig. 32 ) less distinct than between remaining sternites. Propygidium ( Fig. 33 ; prpg) hidden under elytra, strongly sclerotized and densely covered with transverse rows of trichia; pygidium ( Fig. 33 ; pg) exposed in intact specimens, strongly sclerotized, subtriangular with rounded apex, covered with setae.

Female terminalia ( Fig. 36 ). Ovipositor lightly sclerotized and fragile; proctiger ( Fig. 36 ; prc) subtriangular with rounded posterior margin, separated from fused and large paraprocts ( Fig. 36 ; ppr); valvifers ( Fig. 36 ; vf) elongate, distal margin of each with row of setae; coxites fused indistinguishably to valvifers; styli absent.

Spermatheca ( Fig. 37 ) with distal globular and proximal tubular parts, insertion of accessory gland ( Fig. 37 ; iag) located proximally on tubular part of spermatheca; ductus spermathecae ( Fig. 37 ; ds) long and thin; spermatheca in intact specimens located deeply in abdomen or even inside metathorax.

Male terminalia ( Figs. 34–35 ). Sternite IX ( Fig. 34 ; st9) small and membranous; tergite IX ( Fig. 35 ) composed of laterotergites connected by narrow median bridge, each with long lateral apodemes; tergite X ( Fig. 35 ; t10) pentagonal with rounded apical margin.

Aedeagus ( Figs. 38–44 ) bulbous, elongate but relatively stout, with rounded base of median lobe and moderately narrowing apically; ventral wall ( Figs. 38–39, 41–43 ; vw) fused distally with ventral projection ( Figs. 38–39, 41–43 ; vp) and laterally surrounded by narrow membranous area ( Figs. 38, 43 ; ma); apical part of median lobe with strongly sclerotized meso-ventral and meso-dorsal projections ( Figs. 38–39, 41–43 ; mvp, mdp) and elongate copulatory piece ( Figs. 41–42 ; cp) protruding from between meso-dorsal projection and apical part of dorsal wall ( Figs. 41–42 ; adw). Basal orifice ( Fig. 40 ; bo) moderately large, located sub-basally on dorsal wall. Parameres ( Figs. 38–44 ; pm) free (i.e., not fused with median lobe), slender, each with a group of apical setae ( Fig. 44 ). Internal armature of aedeagus in transparent mounts ( Fig. 43 ; ia) visible as darkly sclerotized internal parts of meso-ventral projection, meso-dorsal projection and copulatory piece, endophallus ( Fig. 43 ; end) membranous, variously shaped, usually covered with fine denticles.

Remarks. Most of Palaearctic species of Stenichnus can be easily identified as belonging to this genus already on the basis of the general body shape and especially shapes of the head and pronotum, clearly different than in any other genus of Cyrtoscydmini that occurs in this large area. However, in other regions some genera may be highly similar to Stenichnus and it is necessary to examine the entire set of diagnostic characters to confirm determinations. Stenichnus seems to be most similar to Nearctic Brachycepsis Brendel, 1889 , a taxon previously treated as a subgenus of Stenichnus (elevated to a genus rank by Franz (1985)). Major differences between Stenichnus and Brachycepsis can be found in the shape of mandibles (falciform in Stenichnus vs. subtriangular with a small mesal tooth in Brachycepsis ); in the structure of prosternum (with fine intercoxal carina in Stenichnus vs. with a short, subtriangular intercoxal process in Brachycepsis ); in asetose impressions on the mesoventrite (separated in middle in Stenichnus vs. fused in middle in Brachycepsis ); and in the metaventral intercoxal process (short and broad in Stenichnus vs. long and narrow in Brachycepsis ). It remains to be studied whether Brachycepsis have the labial discs characteristic of Stenichnus ; this character is nearly impossible to notice in intact specimens in dry or transparent preparations, and a SEM study is required to analyze the structure of labium using specimens with the prementum exposed or on isolated mouthparts. For this reason, having only unique type specimens of most of the taxa treated below, with the labium in most cases concealed by maxillae and mandibles, in the present study the labial discs were not used to re-classify the subgenera of Stenichnus . The labial discs within Cyrtoscydmini may be in fact broadly distributed among genera that potentially share a common ancestor with Stenichnus . Other characters, both differences and similarities, are used to clarify the taxonomic status of taxa treated herein.

Figures

FIGURES 1 – 4. Examples of dorsal (1, 2, 4) and lateral (3) habitus of Stenichnus s. str. Stenichnus bicolor (Denny) (1); S. collaris (Müller & Kunze) (2, 3); S. totoro Jałoszyński (4).

FIGURES 5 – 8. Stenichnus (s. str.) collaris (Müller & Kunze). Head in dorsal (5), anterior (6), left lateral (7) and ventral (8) views. Abbreviations: as, antennal socket; ce, compound eye; cl, clypeus; fcg, fronto-clypeal groove; fo, foramen occipitale; fr, frons; gen, gena; gp, gular plate; gs, gular suture; h, hypostoma; hr, hypostomal ridge; lb, labrum; lss, lateral suture of submentum; md, mandible; mn, mentum; mx, maxilla; mxp, maxillary palp; mxp 2 – 4, maxillary palpomere II – IV; nr, neck region; occ, occipital constriction; pmn, prementum; smn, submentum; tm, temple; vt, vertex.

FIGURES 9 – 17. Stenichnus (s. str.) collaris (Müller & Kunze). Mouthparts in dorsal view (9), epipharynx in ventral view (10), base of right mandible in dorsal view (11), mandibles and labrum in ventral view (12), apical part of left mandible in dorsal view (13), maxillae and hypopharynx in dorsal view (14), distal part of right maxillary palp in dorsal view (15), labium and maxillae in ventral view (16), and prementum in anterior view (17). Abbreviations: bp, basal pouch of mandible; bst, basistipes; cd, cardo; cl, clypeus; eph, epipharynx; fcg, fronto-clypeal groove; fr, frons; gal, galea; gl; glandular opening; hph, hypopharynx; lac, lacinia; lb, labrum; ld, labial disc; llh, lateral lobe of hypopharynx; lp 1 – 3, labial palpomere I – III; md, mandible; mn, mentum; ms, marginal sensilla; mst, mesostipes; mv, marginal velum of labrum; mxp 1 – 4, maxillary palpomere I – IV; pmn, prementum; ppf, palpifer; smn, submentum; tr, trichia.

FIGURES 18 – 21. Stenichnus (s. str.) collaris (Müller & Kunze). Prothorax in dorsal (18, 19), left lateral (20) and ventral (21) views. Abbreviations: bf, ante-basal pronotal fovea; bs, basisternal part of prosternum; hy, hypomeron; nss, notosternal suture; pcc, procoxal cavity; pcs, procoxal socket; pn, pronotum; psc, prosternal carina.

FIGURES 22 – 28. Stenichnus (s. str.) collaris (Müller & Kunze). Mesothorax in dorsal view (22), mesothorax in ventral view (23 – 26), meso- and metathorax in dorsal view (27), metathorax in dorsal view (28). Abbreviations: ai, asetose impression of mesoventrite; aest 2, mesanepisternum; aest 3, metanepisternum; alc, alacrista; amc, anterior marginal carina of mesocoxal cavity; anp, anterior notal process; ap, apodema; ar, anterior ridge; bef, basal elytral fovea; el, elytron; mcp, mesocoxal projection; mm, median membranous area; mscc, mesocoxal cavity; mscs, mesocoxal socket; msfa, mesofurcal arm; msff, mesofurcal fovea; msvp, mesoventral intercoxal process; mtap, metaventral anterior process; pl, posterior lobe of mesocoxal projection; pnp, posterior notal process; pre, prepectus; prsc 3, metaprescutum; psn 3, metapostnotum; sc 2, mesoscutellum; sc 3, metascutum; si, setose impression of mesoventrite; scl 2, mesoscutellum; sss, scutoscutellar suture; v 3, metaventrite; wb, wing base.

FIGURES 29 – 31. Stenichnus (s. str.) collaris (Müller & Kunze). Pterothorax in ventral view (29), pterothorax and abdomen in left lateral view (30), ventral internal part of pterothorax in dorsal view (31). Abbreviations: aest 2, mesanapisternum; aest 3, metanepisternum; ai, asetose impression of mesoventrite; amc, anterior marginal carina of mesocoxal cavity; ar, anterior ridge; cx 3, metacoxa; epm 2, mesepimeron; epm 3, metepimeron; fe 3, metafemur; mcp, mesocoxal projection; mscc, mesocoxal cavity; msfa, mesofurcal arm; msvp, mesoventral intercoxal process; mtap, metaventral anterior process; mtfa, metafurcal arm; mtfs, metafurcal stem; mtvp, metaventral intercoxal process; pre, prepectus; si, setose impression of mesoventrite; st 3 – 6, abdominal sternite III – VI; tr 3, metatrochanter; v 2, mesoventrite; v 3, metaventrite.

FIGURES 32 – 37. Stenichnus (s. str.) collaris (Müller & Kunze). Abdomen in ventral (32) and dorsal (33) views, sternite IX of male in ventral view (34), tergites IX and X of male in dorsal view (35), ovipositor in dorsal view (36) and spermatheca (37). Abbreviations: ds, ductus spermathecae; iag, insertion of accessory gland; pg, pygidium; ppr, paraproct; prc, proctiger; prpg, propygidium; st 3 – 8, abdominal sternite III – VIII; st 9, abdominal sternite IX; t 9 – 10, abdominal tergite IX – X; vf, valvifer.

FIGURES 38 – 44. Stenichnus (s. str.) collaris (Müller & Kunze). Aedeagus in ventral (38), lateral (39, 43), dorsal (40), ventroapical (41), and apical (42) views, and apex of paramere (44). Abbreviations: adw, apex of dorsal wall; bo, basal orifice; cp, copulatory piece; dw, dorsal wall; end, endophallus; lw, lateral wall; ma, membranous area; mdp, meso-dorsal projection; mvp, meso-ventral projection; pm, paramere; vp, ventral projection; vw, ventral wall.