Leptochromus Motschulsky
Creators: name: Paweł Jałoszyński
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Staphylinidae
Leptochromus

description: Leptochromus Motschulsky
Leptochromus Motschulsky, 1855: 12. Type species: Leptochromus fulvescens Motschulsky, 1855 (monotypy). Hecotus Sharp, 1887: 70. Type species: Hecotus mexicanus Sharp, 1887 (des. Franz in Newton & Franz (1998)). Synonymized with Leptochromus 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); 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 –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, 119–120, 124, 127–129) 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; gp) lacking sutures, nearly smooth; posterior tentorial pits (Figs 124, 129; ptp) arcuate, in front of transverse impression demarcating 'neck' region ventrally; hypostomal ridges (Figs 124, 129; hr) nearly straight or arcuate, posteriorly reaching middle between anterior submental margin and posterior tentorial pits. Postgenae (Figs 115–116, 119– 120, 124, 127–129) 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).
Antennae (Figs 107 –109, 114–116, 127) shorter or slightly longer than body, slender; scape (Figs 114–116, 127; 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, 127; 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, 129) with large but relatively short cardo (Fig. 124; cd); basistipes (Fig. 124; bst) subtriangular and elongate; mediostipes (Fig. 124; 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; ppf) broad and elongate; maxillary palp (Figs 114, 116, 121, 127, 129) conspicuously long, much longer than head capsule, composed of minute palpomere I (Fig. 121; mxp1), extremely elongate, slender, only slightly broadening distad palpomere II (Fig. 121; mxp2), which is distinctly recurved and bearing a long, slender bifurcate cuticular process with two apical bristles, palpomere III (Fig. 121; mxp3) strongly elongate, slender, broadened only slightly in its distal third or fourth, with transverse distal margin, palpomere IV (Fig. 121; 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, 129) with broad and short submentum (Fig. 124; smn) posteriorly not demarcated from gular region, bearing a pair of long thin setae in its subanterior region; mentum (Fig. 124; mn) subtrapezoidal and strongly transverse, with anterior margin weakly concave; prementum (Fig. 124; 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; lhl) moderately large; labial palp (Fig. 124; 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, 125, 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; prcl) demarcated by a dorsal transverse row of several variously distinct pits connected by a groove. Prosternum (Figs 125, 130) with basisternal part (Fig. 125; bstr) much longer than coxal part (Fig. 125; 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, 132) subtrapezoidal, broadening posteriorly. Prepecti (Fig. 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; si), margins of impression are obscured by setae (Fig. 132). Region just behind collar strongly and abruptly constricted, ventrally forming setose impression (Figs 126, 132; si) filled with dense, unmodified setae. Mesoventral intercoxal process (Figs 126, 132; 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; 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, 126, 132) 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; mtvp) with variously deeply concave posterior margin and subtriangular posterolateral corners; metaventrite with lateral mesocoxal (Figs 123, 126; lmcf) and postmesocoxal (Figs 123, 126; pmcf) foveae. Posterior metaventral margin lacking adcoxal carinae. Metanepisterna (Fig. 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; lmfa), additionally with median longitudinal projection.
Legs (Figs 107 –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, 125, 130) 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, 130). 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, 131) oval, strongly convex, with prominent humeral calli (Fig. 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) with sternite III not fused with metaventrite, about as long as sternites IV and V together; sternite VIII in male distinctly emarginate (Fig. 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), and one extinct species (Fig. 110) 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). 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).
description: Published as part of Paweł Jałoszyński, 2018, World genera of Mastigitae: review of morphological structures and new ecological data (Coleoptera: Staphylinidae: Scydmaeninae), pp. 1-119 in Zootaxa 4453 (1) on pages 53-62, DOI: 10.11646/zootaxa.4453.1.1, http://zenodo.org/record/1454920