Leptochromus Motschulsky

Paweł Jałoszyński, 2018, World genera of Mastigitae: review of morphological structures and new ecological data (Coleoptera: Staphylinidae: Scydmaeninae), Zootaxa 4453 (1), pp. 1-119 : 53-62

publication ID	https://doi.org/ 10.11646/zootaxa.4453.1.1
publication LSID	lsid:zoobank.org:pub:866690A9-0462-4892-AE29-9AAC623F87B3
DOI	https://doi.org/10.5281/zenodo.5976946
persistent identifier	https://treatment.plazi.org/id/2161879C-FFF2-8A2E-FF7A-358C633CDF8F
treatment provided by	Plazi
scientific name	Leptochromus Motschulsky
status

Treatment

Leptochromus Motschulsky View in CoL

Leptochromus Motschulsky, 1855: 12 View in CoL . Type species: Leptochromus fulvescens Motschulsky, 1855 View in CoL (monotypy). Hecotus Sharp, 1887: 70 View in CoL . Type species: Hecotus mexicanus Sharp, 1887 View in CoL (des. Franz in Newton & Franz (1998)). Synonymized with Leptochromus View in CoL by Csiki (1919).

Diagnosis. Leptochromus differs from all remaining Leptochromini in unique apomorphies: maxillary palpomere II with a long and slender cuticular projection with bifurcate apex and a pair of thick apical bristles ( Fig. 121 View FIGURES 119–123 ); and maxillary palpomere IV strongly elongate, nearly as long as palpomere III, only slightly broadened in subapical region and with subconical apex.

Characteristics. Adults. Body ( Figs 107 View FIGURES 107–108 –109) moderately large, 2.70̄ 4.20 mm in length, from yellowish to dark brown, strongly convex or slightly flattened, dorsally densely setose, setae long and suberect to erect, unmodified except for several long and thick bristles on protrochanters, postgenae, and maxillary palpomere II.

Head capsule ( Figs 114–116 View FIGURES 114–118 , 119–120 View FIGURES 119–123 , 124 View FIGURES 124–126 , 127–129 View FIGURES 127–131 ) divided into large and exposed anterior part and much smaller, subcylindrical 'neck' region retracted into prothorax and demarcated by distinct occipital constriction; 'neck' region about as broad as half width of head. Anterior part of head strongly flattened, subequal in width with prothorax, strongly transverse, broadest at eyes, slightly in front of middle. Composite eyes dorsolateral, near anterior margin of head, moderately large, composed of numerous small ommatidia, strongly convex. Vertex strongly transverse and posteriorly impressed at middle, convex at sides, with posterior margin concave. Tempora long and rounded. Frons between antennal insertions with straight margin, not forming a demarcated 'platform', anteriorly demarcated by a deep and complete frontoclypeal groove. Clypeus very short and broad, with rounded or straight sides. Antennal insertions located anterodorsally, very broadly separated. Gular plate ( Fig. 129 View FIGURES 127–131 ; gp) lacking sutures, nearly smooth; posterior tentorial pits ( Figs 124 View FIGURES 124–126 , 129 View FIGURES 127–131 ; ptp) arcuate, in front of transverse impression demarcating 'neck' region ventrally; hypostomal ridges ( Figs 124 View FIGURES 124–126 , 129 View FIGURES 127–131 ; hr) nearly straight or arcuate, posteriorly reaching middle between anterior submental margin and posterior tentorial pits. Postgenae ( Figs 115–116 View FIGURES 114–118 , 119– 120 View FIGURES 119–123 , 124 View FIGURES 124–126 , 127–129 View FIGURES 127–131 ) in most species with a tubercle or projection (postgenal or subocular process) with 2–3 thick apical bristles. Head with or without punctures, densely setose ( Fig. 115 View FIGURES 114–118 ).

Antennae ( Figs 107 View FIGURES 107–108 –109, 114–116, 127) shorter or slightly longer than body, slender; scape ( Figs 114–116 View FIGURES 114–118 , 127 View FIGURES 127–131 ; sc) 6 to more than 10 times as long as broad, usually slightly broadening distad, longer than head, with very deep lateroventral emargination; pedicel ( Figs 114, 115 View FIGURES 114–118 , 127 View FIGURES 127–131 ; pd) subequal in length to antennomere III or shorter and broadening from narrow base to apex; antennomeres III–XI elongate (usually strongly, rarely weakly) and weakly thickening distad, basal stalks not exposed, basal rings absent or indistinct; antennomere XI elongate and slightly asymmetrical. Antennomeres covered with variously dense, long setae; surface of antennomeres smooth.

Mouthparts. Labrum strongly transverse, with lateral margins divergent anterad, nearly straight or weakly rounded, and with anterior margin concave, with a pair of broad and short submedian teeth separated at middle by a relatively shallow emargination, and with a transverse dorsoanterior row of long setae. Mandibles symmetrical, subtriangular and robust, each with two subapical teeth, at least one of them above the coronal plane of mandible, setose prostheca present and long. Maxilla ( Figs 124 View FIGURES 124–126 , 129 View FIGURES 127–131 ) with large but relatively short cardo ( Fig. 124 View FIGURES 124–126 ; cd); basistipes ( Fig. 124 View FIGURES 124–126 ; bst) subtriangular and elongate; mediostipes ( Fig. 124 View FIGURES 124–126 ; mst) large and sharply demarcated from lacinia and galea, which are both elongate and curved mesally and each with dense row of distal setae; palpifer ( Fig. 124 View FIGURES 124–126 ; ppf) broad and elongate; maxillary palp ( Figs 114, 116 View FIGURES 114–118 , 121 View FIGURES 119–123 , 127, 129 View FIGURES 127–131 ) conspicuously long, much longer than head capsule, composed of minute palpomere I ( Fig. 121 View FIGURES 119–123 ; mxp1), extremely elongate, slender, only slightly broadening distad palpomere II ( Fig. 121 View FIGURES 119–123 ; mxp2), which is distinctly recurved and bearing a long, slender bifurcate cuticular process with two apical bristles, palpomere III ( Fig. 121 View FIGURES 119–123 ; mxp3) strongly elongate, slender, broadened only slightly in its distal third or fourth, with transverse distal margin, palpomere IV ( Fig. 121 View FIGURES 119–123 ; mxp4) nearly rod-like, strongly elongate, slender, only slightly shorter than III, slightly broadened distad up to its distal third and then narrowed to subconical and blunt apex. Palpomeres IĪIV round or nearly round in crosssection, covered with moderately long setae. Labium ( Figs 124 View FIGURES 124–126 , 129 View FIGURES 127–131 ) with broad and short submentum ( Fig. 124 View FIGURES 124–126 ; smn) posteriorly not demarcated from gular region, bearing a pair of long thin setae in its subanterior region; mentum ( Fig. 124 View FIGURES 124–126 ; mn) subtrapezoidal and strongly transverse, with anterior margin weakly concave; prementum ( Fig. 124 View FIGURES 124–126 ; pm) long, subtrapezoidal, broadest distally, lacking demarcated ligula, with one or two pairs of anterolateral setae, with broadly separated bases of labial palps; lateral hypopharyngeal lobes ( Fig. 124 View FIGURES 124–126 ; lhl) moderately large; labial palp ( Fig. 124 View FIGURES 124–126 ; lp) composed of three palpomeres: palpomere I small, weakly elongate, broadening distad, palpomere II largest, strongly elongate and barrel-shaped, palpomere III narrow, long and pointed. Porous fields on mouthparts and clypeus not found.

Prothorax ( Figs 107–108 View FIGURES 107–108 , 125 View FIGURES 124–126 , 131 View FIGURES 127–131 ) elongate, strongly convex, broadest near anterior third or at least distinctly in front of middle. Pronotum with anterior and posterior margins arcuate or nearly straight, sides rounded in anterior half and sinuate in posterior half; anterior and posterior corners obtuse-angled; pronotal base with a short posterior 'collar' ( Fig. 131 View FIGURES 127–131 ; prcl) demarcated by a dorsal transverse row of several variously distinct pits connected by a groove. Prosternum ( Figs 125 View FIGURES 124–126 , 130 View FIGURES 127–131 ) with basisternal part ( Fig. 125 View FIGURES 124–126 ; bstr) much longer than coxal part ( Fig. 125 View FIGURES 124–126 ; cxst). Prosternum laterally completely fused with hypomera. Coxal region demarcated anteriorly by carina extending laterally up to apices of very weakly developed adcoxal hypomeral lobes. Procoxal cavities broadly open. Prosternal intercoxal process indistinct or absent. Ventral surface of prothorax densely setose.

Mesoventrite ( Figs 126 View FIGURES 124–126 , 132 View FIGURES 132–134 ) subtrapezoidal, broadening posteriorly. Prepecti ( Fig. 126 View FIGURES 124–126 ; pre) long and together with anteromedian mesoventral area forming a massive 'collar', which bears an indistinct transverse groove just behind its anterior ridge, posterior margin of collar broadly subtriangular, only slightly projecting posterad at middle, tip of this median projection is broadly separated from a similar anteromedian projection of posterior margin of setose impression ( Fig. 126 View FIGURES 124–126 ; si), margins of impression are obscured by setae ( Fig. 132 View FIGURES 132–134 ). Region just behind collar strongly and abruptly constricted, ventrally forming setose impression ( Figs 126 View FIGURES 124–126 , 132 View FIGURES 132–134 ; si) filled with dense, unmodified setae. Mesoventral intercoxal process ( Figs 126 View FIGURES 124–126 , 132 View FIGURES 132–134 ; msvp) long, narrow and weakly elevated, nearly parallel-sided or indistinctly broadened near middle of mesocoxal cavities, fully separating mesocoxae, posteriorly with indistinct posterior tip, which is fused with metaventrite. Mesanepisterna large and subtriangular; mesepimera partly exposed in ventral view.

Mesonotum with subtriangular, strongly elongate mesoscutellum ( Fig. 122 View FIGURES 119–123 ; scl2) with pointed or rounded apex, in intact specimens only its very tip visible between elytral bases; scutoscutellar suture absent.

Metanotum and hind wings fully developed.

Metaventrite ( Figs 123 View FIGURES 119–123 , 126 View FIGURES 124–126 , 132 View FIGURES 132–134 ) short, subquadrate or subrectangular and slightly transverse, with lateral margins rounded; mesocoxal cavities not carinate; posterior margin of metaventrite deeply bisinuate laterally (in front of each metacoxa) and with a broad metaventral intercoxal process ( Fig. 126 View FIGURES 124–126 ; mtvp) with variously deeply concave posterior margin and subtriangular posterolateral corners; metaventrite with lateral mesocoxal ( Figs 123 View FIGURES 119–123 , 126 View FIGURES 124–126 ; lmcf) and postmesocoxal ( Figs 123 View FIGURES 119–123 , 126 View FIGURES 124–126 ; pmcf) foveae. Posterior metaventral margin lacking adcoxal carinae. Metanepisterna ( Fig. 126 View FIGURES 124–126 ; aest3) broad and partly visible in ventral view, broadened posteriorly; metepimera broader than metanepisterna, with indistinctly demarcated inner and outer component, posteriorly extending far behind metacoxae.

Metendosternite (metafurca) with stem much broader than long and broadly separated divergent lateral furcal arms ( Fig. 126 View FIGURES 124–126 ; lmfa), additionally with median longitudinal projection.

Legs ( Figs 107 View FIGURES 107–108 –109, 117–118, 126, 130, 132) conspicuously long, slender. Pro- and mesocoxa short subconical, metacoxa with nearly hemispherical basal part and subconical distal part. Mesocoxa lacking coxal bristles, but usually with a row or patch of thin long setae. All trochanters short and subtriangular; protrochanters ( Figs 118 View FIGURES 114–118 , 125 View FIGURES 124–126 , 130 View FIGURES 127–131 ) in both sexes with a row of several thick bristles (in one species reduced to 1–2). Femora weakly clavate, profemur in both sexes with a ventral row of several conspicuously thick bristles, usually with papillate insertions ( Figs 118 View FIGURES 114–118 , 130 View FIGURES 127–131 ). Tibiae slender, protibiae in both sexes curved, only rarely nearly straight. Tarsi long and slender, nearly subcylindrical, tarsomeres I–V subequal or reducing in length, tarsomere V strongly elongate, with curved and slender claws lacking elongate costae; empodial region was not studied.

Elytra ( Figs 107–108 View FIGURES 107–108 , 131 View FIGURES 127–131 ) oval, strongly convex, with prominent humeral calli ( Fig. 131 View FIGURES 127–131 ; hcl), lacking basal impressions, with rounded apices; elytral disc with distinct large and deep punctures arranged in six nearly complete and typically regular longitudinal rows. Elytra variously densely setose, setae long and erect.

Abdomen ( Fig. 132 View FIGURES 132–134 ) with sternite III not fused with metaventrite, about as long as sternites IV and V together; sternite VIII in male distinctly emarginate ( Fig. 134 View FIGURES 132–134 ).

Aedeagus (illustrated in Jałoszyński et al. (2018), Lord et al. (2014) and O’Keefe (2002)) strongly elongate, with symmetrical median lobe, parameres heavily sclerotized, symmetrical, with arrowhead-shaped or spatulate and pointed apices; flagellum simple, not coiled. Ejaculatory duct with elongate and narrow sperm pump lacking funnel-like structures. Aedeagus in repose positioned symmetrically inside abdomen, with basal orifice facing up.

Spermatheca (illustrated by O’Keefe (2002)) globular, nearly spherical, with relatively large accessory gland.

Larva. Unknown.

Composition and distribution. Leptochromus comprises five extant species distributed in Brazil, Colombia, Costa Rica and Panama ( Fig. 113 View FIGURE 113 ), and one extinct species ( Fig. 110 View FIGURES 110–112 ) found in the Middle Miocene Chiapas amber.

Natural history. Little is known about natural history of Leptochromus , except collecting circumstances for some species. Adults were collected from moist leaf litter, moss and lichens in subtropical forests ( Figs 135–137 View FIGURES 135–137 ). Numerous individuals of Leptochromus laselva were collected "lifting dead palm fronds lying on the floor of secondary-growth forest (...) and beating them over a white sheet during late afternoon and early evening hours" (Lord et al. 2014). The latter authors also noted that although adults of L. laselva are fully winged, no individuals were collected at light (including UV) for two weeks at the collecting site. Leptochromus fulvescens and L. laselva were also collected by canopy fogging, demonstrating that members of this genus are active not only on the forest floor (Lord et al. 2014).

The unusual modifications of the maxillary palpomere II and postgenae may be used by beetles as a sensory and/or prey-capture apparatus, but hunting and feeding-related behavior of Leptochromus have not been observed.

Remarks. All nominal extant and extinct species of Leptochromus were adequately described or redescribed by O’Keefe (2002) and Lord et al. (2014).