Leptomastacini Casey 1815
Creators: name: Paweł Jałoszyński
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Scydmaenidae

description: Tribe Leptomastacini Casey
Leptomastacini Casey, 1897: 541. Type genus: Leptomastax Pirazzoli, 1855.
Diagnosis. Leptomastacini differ from all other Mastigitae in several unique apomorphies: maxillary palpomeres IIĪIV forming a compact oval, with distal margin of palpomere III and basal margin of IV strongly oblique, and palpomere IV broader than long (e.g. Fig. 17); most antennal flagellomeres transverse (e.g. Fig. 14); body with numerous modified setae (thickened, lanceolate or leaf-like) (e.g. Figs 19, 21, 65, 67), especially submental setae always conspicuously thickened (e.g. Fig. 15); basisternal part of prosternum largely asetose (even in taxa with dense setae on other body parts) except for rows of modified setae along anterior and posterior margins and rarely some median setae (e.g., Figs 18, 66); metaventrite with three pairs of anterolateral foveae (e.g., Fig. 20); aedeagus with symmetrical median lobe and parameres, but in repose positioned asymmetrically inside abdomen (Fig. 20). Additionally, Leptomastacini have a set of synapomorphies that occur in other genera, but never all together: mandible with one mesal tooth or lacking teeth; hypostomal ridges reaching to about middle between anterior submental margin and posterior tentorial pits; anterior and posterior margins of mesoventral setose impression with subtriangular or subtrapezoidal median asetose projections, so that the impression is horizontally 8-shaped (e.g., Fig. 24); mesoventral intercoxal process slender, weakly but distinctly narrowing posterad (e.g., Fig. 21); and a row of several (3–5) long and thick coxal bristles on each mesocoxa (e.g., Fig. 25).
Characteristics. Adults. Body small, 1.10̄2.89 mm in length, slender and flattened, usually light brown or even pale yellowish, rarely moderately dark brown, covered with setae, of which all or some are modified, thickened, lanceolate or short and leaf-like.
Head of various shape, about as long as broad or transverse; antennal insertions anterodorsal, broadly separated, and each broadly separated from side of head and from mandibular base; vertex transverse, distinctly demarcated from 'neck' region, with a pair of conspicuously large posterolateral setiferous punctures; frons confluent with vertex, forming a subtriangular 'platform' between antennal insertions with step-wise anterolateral margins; clypeus strongly transverse; eyes vestigial or absent, often reduced to one ommatidium at each side located laterally at the level of antennal insertions. Gular plate transversely reticulated; posterior tentorial pits small, slot-like, C-shaped or straight; hypostomal ridges arcuate, posteriorly extending to middle between anterior submental margin and posterior tentorial pits. Postgenae with variously distinct longitudinal ridges, each extending anterad ventrally from occipital constriction (in one genus ridges absent).
Antennae moderately slender, shorter than body; scape weakly but distinctly enlarged, subequal to length of head, about as long as 3 subsequent antennomeres, with distinct, deep ventral or ventrolateral apical emargination; pedicel weakly elongate, subtriangular, 1/2̄1/3 as long as scape; antennomeres IIĪX transverse or some about as long as broad, rarely antennomere X indistinctly elongate; antennomere XI elongate and slightly asymmetrical. Antennomeres IIĪXI each with narrow subcylindrical basal stalk and sharp basal marginal ring; all antennomeres densely covered with modified setae of two forms, short and subcylindrical or lanceolate, and long and lanceolate, setae inserted on small papillate elevations, so the surface of antennomeres appears coarse.
Mouthparts. Labrum strongly transverse and with a deep anteromedian subtriangular emargination, with only a few dorsal setae. Mandibles symmetrical, each with one mesal tooth shifted slightly dorsad, or lacking teeth, subtriangular and robust or extremely slender and falciform, if subtriangular than with setose prostheca, when falciform then lacking prostheca. Maxillae generalized, as in all Scydmaeninae, except for maxillary palps, which have palpomeres III and IV forming a compact oval, without any constriction between strongly oblique apex and base of palpomeres III and IV; palpomere IV broader than long, rounded at apex; all palpomeres densely covered with modified setae. Submentum transverse, with a pair of long and conspicuously thick setae near anterior margin; submentum subtrapezoidal, with anterior margin straight or nearly straight; prementum prominent, largely membranous, with its anteromedian surface devoid of setae; insertions of labial palps broadly separated, labial palpomere I small and weakly elongate, palpomere II strongly enlarged, long and broadening distad; palpomere III narrow and distinctly longer than half length of palpomere II (in one genus palpomeres II and III subequal in length), pointed at apex.
Pronotum elongate (sometimes weakly so), broadest in anterior third or fourth, with anterior and posterior margins nearly straight or arcuate, anterior corners broadly rounded, posterior corners strongly obtuse-angled, sides rounded, sometimes nearly straight in posterior half; pronotal base lacking pits or groove. Prosternum laterally fused with hypomera, but sometimes with traces of notosternal sutures marked just at anterior sternal margin or near procoxal cavities, with basisternal part about as long as coxal part or distinctly longer, largely asetose, only with a row of setae along anterior and posterior margin, in one genus additionally with some median setae; coxal part demarcated anteriorly and laterally by complete arcuate ridge extending posteriorly to postcoxal hypomeral lobes; prosternal carina short, narrow or diffuse and weakly elevated, not separating procoxae; procoxal cavities broadly open; each hypomeron behind procoxal cavity forming a small subtriangular postcoxal hypomeral lobe directed mesad.
Mesoscutellum in intact beetles not visible between elytral bases, subtriangular or subtrapezoidal; scutoscutellar suture absent.
Metanotum largely membranous, but with only slightly shortened alacristae; hind wings absent.
Mesoventrite with prepecti and anteromedian area forming a massive transverse scaly sculptured ring or 'collar' inserted into prothorax, with a shallow and strongly transverse medioventral impression just behind anterior ridge, ventral area behind collar strongly concave, forming transverse setose impression filled with modified, dense and leaf-like setae, anteromedian and posteromedian margins of setose impression each with asetose subtriangular or subtrapezoidal projection directed respectively posterad and anterad, so that setose impression is horizontally 8- shaped. Mesoventral intercoxal process slender and elongate, weakly but distinctly narrowing posterad, weakly convex or nearly flat, posteriorly fused with metaventrite. Mesepimera partly exposed in ventral view, demarcated from mesanepisterna by a ridge or fused, and from metepimera by an indistinct suture.
Metaventrite subquadrate or slightly transverse; mesocoxal cavities with their anterior and posterior margins carinate; posterior adcoxal margin of ventrite strongly concave and with short adcoxal carina at each side; metaventral intercoxal process very short and broad, with concave or nearly straight posterior margin and subtriangular posterolateral corners. Metanepisterna broad or narrow, exposed in ventral view; metepimera very broad. Metaventrite with three pairs of foveae: lateral meso-metaventral foveae between meso- and metaventrite laterad mesocoxal insertions; lateral mesocoxal foveae posterolaterad mesocoxal insertions; and postmesocoxal foveae posterad mesocoxal cavities. In one genus metaventrite with median longitudinal carina.
Elytra elongate, oval, lacking humeral calli, basal impressions and basal foveae; in one genus each elytron with one basal or sub-basal setiferous puncture. Elytral disc with longitudinal rows of punctures, in some species weakly marked.
Abdomen longer than metaventrite, with 6 sternites visible; sternite III (first visible) much longer than each of IV̄VIII; posterior margin of sternite VIII in males not emarginate; suture between sternite VII and VIII distinct.
Aedeagus elongate, weakly sclerotized (translucent), with symmetrical median lobe and symmetrical parameres, their apices rapidly curved mesad; flagellum straight or nearly straight. Aedeagus in repose asymmetrically positioned inside abdomen.
Spermatheca globular or strongly elongate.
Characteristics. Larvae. Only larva of the Mediterranean Leptomastax hypogea Pirazzoli, 1855 was described (Vít & De Marzo 1989); description given at Leptomastax.
Composition and distribution. Leptomastacini currently comprise 30 species and subspecies classified into three genera. All species occur in the Western Palaearctic region, predominantly in the northern and eastern part of the Mediterranean Basin, with a few representatives known from the southern Carpathians, western Caucasus and the southern coastal region of Caspian Sea ("Hyrcania") (Figs 7–9).
Remarks. Leptomastacini are adapted to subterranean life, which is reflected by their small and flattened bodies, light pigmentation and reduction of composite eyes, wings and associated structures of the wing base. They have many unique apomorphies and are one of the best defined tribes, strongly supported as monophyletic unit in phylogenetic analyses (Jałoszyński 2012b, 2016a; Jałoszyński et al. 2018). In addition to characters given in the diagnosis, Leptomastacini may also be unique among Mastigitae (and all Scydmaeninae) in having the tarsal claws with longitudinal costae (Figs 76–77), but further study is required to verify whether it is stable or variable within genera.
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 12-14, DOI: 10.11646/zootaxa.4453.1.1, http://zenodo.org/record/1454920