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

description: Leptomastax Pirazzoli
Leptomastax Pirazzoli, 1855: 3. Type species: Leptomastax hypogeum Pirazzoli, 1855 (monotypy).
Pyladus Fairmaire, 1856a: 179. Type species: Pyladus coquereli Fairmaire, 1856 a (monotypy). Synonymized with Leptomastax by Fairmaire (1856b).
Pylades Fairmaire, 1856b: 526. Type species: Pylades coquereli Fairmaire, 1856a (monotypy). Probably a misspelling of Pyladus.
Leptomastoides Karaman, 1962: 170 (as subgenus of Leptomastax; nomen nudum, no type species designated; treated as synonym of Leptomastax by Castellini (1996)).
Diagnosis. Leptomastax differs from other Leptomastacini in the following unique apomorphies: very large and flat head which is often broader than prothorax and strongly transverse (Figs 29–31); mandibles extremely long and slender, falciform and lacking mesal teeth (Figs 29–31); body appears asetose and only under high magnification flattened and broadened setae can be seen on antennae, maxillary palps, prosternum, and in foveate structures of metaventrite and first visible abdominal sternite (Figs 33–34, 37, 42); metanepisterna conspicuously narrow, so that in ventral view entirely visible, and also extremely broad metepimera partly exposed in intact beetles (Figs 42–44). Additionally, 'neck' region is subequal to half width of head, a character known in other tribes of Scydmaeninae, but not in other Leptomastacini; and postgenae have indistinct longitudinal ridges (Fig. 30; lr) (among Mastigitae present also in Ablepton).
Characteristic. Adult. Body (Figs 3–4) small, 1.24̄2.89 mm in length, light brown or yellowish, flattened, dorsally virtually asetose, setae mostly modified, either flattened and broadened but strongly elongate or very short and broad, leaf-like, distributed mostly on antennae and ventral side of thorax.
Head capsule (Figs 29–32) divided into large and exposed anterior part and much smaller, rounded and flattened '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 and remarkably broad, strongly transverse and as broad as pronotum or broader, broadest at anterior margin. Composite eyes (Fig. 29; ce) dorsolateral, near anterior margin of head, from moderately large and composed of about a dozen ommatidia to very small and indistinct, in some cases only one small ommatidium present (barely discernible under stereoscopic microscope); eyes, even when large, flat, in dorsal view not projecting laterad. Vertex strongly transverse and weakly, evenly convex, with posterior margin straight or nearly straight at middle and a pair of long posterolateral setae (often only setiferous punctures remain; Fig. 29; sp). Tempora very long and rounded. Frons between antennal insertions forming a short and broad subtrapezoidal 'platform', entire frons anteriorly demarcated by a deep, narrow frontoclypeal groove (Fig. 29; fcg) obliterated laterally. Clypeus very short and broad, with rounded sides. Antennal insertions (Fig. 29; ai) located dorsally in submedian area of head, broadly separated. Gular plate (Fig. 30; gp) lacking sutures, transversely reticulated; posterior tentorial pits (Figs 30, 32; ptp) arcuate, in front of transverse impression demarcating 'neck' region ventrally; hypostomal ridges (Fig. 30; hr) arcuate, posteriorly reaching middle between anterior submental margin and posterior tentorial pits. Head impunctate or very finely punctate and dorsally asetose.
Antennae (Figs 3–4, 29–30, 33) much shorter than body; scape (Figs 29–31; sc) 4̄5 times as long as broad, often with dorsal longitudinal ridge; pedicel (Figs 30–31; pd) distinctly longer than antennomere III and strongly broadening from narrow base to apex; antennomeres III–X mostly transverse and weakly thickening distally, each with narrow and short basal stalk and sharp basal ring; antennomere XI elongate and slightly asymmetrical. Antennomeres covered with dense and evenly distributed short and slightly flattened setae and much longer, strongly flattened and broadened sparse setae around distal margin of each antennomere except I, II and XI (Fig. 33); all setae inserted on small papillae, so that surface of antennomeres appears coarse.
Mouthparts. Labrum (Fig. 29; lbr) strongly transverse, with slightly concave or straight and anteriorly strongly convergent lateral margins and anterior margin with a deep subtriangular emargination occupying nearly its entire width; dorsal surface with only several long and thick setae anteriorly. Mandibles (Figs 29–31, 35–36) symmetrical, each extremely long and slender, longer than head, falciform, without mesal teeth and without prostheca, mandible in cross-section nearly circular or oval, surface near base with dense oblique rugae and in distal part with longitudinal grooves (Figs 35–36). Maxilla (Fig. 30) with large but relatively short cardo (Fig. 30; cd); basistipes (Fig. 30; bst) subtriangular and elongate; mediostipes (Fig. 30; mst) large and sharply demarcated from lacinia and galea, which are both elongate and curved mesad and with dense row of distal flattened setae; palpifer (Fig. 30; ppf) broad and elongate; maxillary palp composed of minute palpomere I (Fig. 30; mxp1), elongate and broadening distally palpomere II (Figs 30–31; mxp2), and palpomeres III (Figs 30–31, 34; mxp3) and IV (Figs 30–31, 34; mxp4) forming large compact oval, in which palpomere III is pedunculate and with strongly oblique apex and palpomere IV is broader than long and broadly subconical with rounded but distinctly marked apex. All palpomeres densely covered with lanceolate setae, only IV mostly with short and subcylindrical setae with admixture of lanceolate ones (Fig. 34). Labium (Fig. 30) with broad submentum (Fig. 30; smn) posteriorly not demarcated from gular region and laterally indistinctly demarcated from postcardinal portions of hypostomae by incomplete and weakly marked ridges, bearing a pair of long and thickened setae near its anterior margin; mentum (Fig. 30; mn) subtrapezoidal and strongly transverse, with anterior margin slightly concave; prementum (Fig. 30; pm) long, subtrapezoidal, broadest distally, lacking demarcated ligula, with broadly separated bases of labial palps (Fig. 30; lp); lateral lobes of hypopharynx moderately large; labial palp (Fig. 30; lp) composed of three palpomeres: palpomere I small, elongated, palpomere II largest, strongly elongated and slightly broadening distad, palpomere III narrow, long and pointed. All mouthparts and clypeus covered with sparsely distributed porous fields.
Prothorax (Figs 37–39) flattened and elongate, broadest near anterior third or fourth. Pronotum with all margins rounded or sides in posterior half nearly straight; anterior corners broadly rounded, posterior corners indistinct, obtuse-angled and often completely rounded; pronotal base lacking pits, impressions, grooves or carinae. Prosternum (Figs 37–39) with basisternal part (Fig. 37; bstr) twice or more as long as coxal part (Fig. 39; cxst), laterally completely fused with hypomera but lateroposteriorly with short remnants of notosternal sutures (Fig. 37; nss) extending to 1/4 or less of basisternal length. Coxal region demarcated anteriorly by carina extending laterally up to apices of subtriangular adcoxal hypomeral lobes projecting mesad. Procoxal cavities broadly open. Prosternal intercoxal process narrowly subtriangular and posteriorly carinate, sharply demarcated laterally and weakly elevated, so that procoxae are not separated. Ventral surface of prothorax largely asetose and glabrous; sparse leaf-like setae distributed only along anterior and posterior margins of basisternal area (Figs 37, 39).
Mesoventrite (Figs 40, 42–44) subtrapezoidal, broadening posteriorly. Prepecti long and together with anteromedian mesoventral area form a massive continuous 'collar', which bears a transverse groove just behind its anterior ridge, its posterior margin deeply bisinuate with subtriangular or subtrapezoidal posteromedian projection, which meets a similar anteromedian projection of posterior margin of setose impression (Figs 40, 42–43; si), separating the latter into two lateral halves. Region just behind collar strongly and abruptly constricted, ventrally forming setose impression (Figs 40, 42–43; si) filled with dense, strongly flattened, leaf-like setae. Mesoventral intercoxal process (Figs 40, 42; msvp) long, narrow and weakly convex but distinctly carinate at middle, fully separating mesocoxae, weakly but distinctly narrowing posterad and fused with metaventrite. Mesanepisterna (Fig. 44; aest2) large and subtriangular, fused with mesepimera (Fig. 44; epm2), the latter partly exposed in ventral view (Figs 40, 42).
Mesonotum with subtriangular and pointed mesoscutellum (Fig. 41; scl2), which in intact specimens is visible only between basal elytral articulating lobes; scutoscutellar suture absent.
Metanotum largely membranous, but with alacristae only slightly shortened; hind wings absent.
Metaventrite (Figs 42–44) short, subquadrate, with lateral margins rounded; mesocoxal cavities with marginal carina encompassing each cavity nearly entirely, except narrow lateral area; posterior margin of metaventrite deeply bisinuate laterally (in front of each metacoxa) and with a broad metaventral intercoxal process (Fig. 42; mtvp) with a deeply concave posterior margin and subtriangular posterolateral corners; metaventrite with three pairs of foveae, whose openings are filled with leaf-like setae: lateral meso-metaventral foveae (Figs 42–44; lmf) laterad mesocoxal insertions; lateral mesocoxal foveae (Fig. 43; lmcf) posterolaterad mesocoxal insertions; and postmesocoxal foveae (Figs 42–44; pmcf) posterad mesocoxal cavities, in submedian region of ventrite. External admetacoxal part of posterior metaventral margin with additional marginal thickening demarcated by a groove, forming adcoxal carinae (Fig. 42; acxc) at each side. Metanepisterna (Figs 42–44; aest3) entirely visible in ventral view, very narrow, narrowing both anterad and posterad; metepimera (Figs 42–44; epm3) more than eight times as broad as metanepisterna, with indistinctly demarcated inner and outer component, posteriorly extending far behind metacoxae.
Metendosternite (metafurca) Y-shaped, with short but distinct stem and divergent lateral furcal arms, additionally with short anteromedian projection.
Legs (Figs 3–4, 40, 42–43) moderately long, slender. Pro- and mesocoxa short subconical, metacoxa with nearly hemispherical basal part and subconical distal part. Mesocoxa with impressed lateral adtrochanteral area, border between concave and convex surface with 3̄4 long coxal bristles (Fig. 40; cxb). All trochanters short and subtriangular. Femora weakly clavate. Tibiae robust, all nearly straight. Tarsi short but slender, nearly subcylindrical, tarsomeres reducing in length but not in width from I to IV, tarsomere V strongly elongate, with curved and slender claws and small empodium bearing a pair of lanceolate empodial setae.
Elytra (Figs 3–4, 41) oval, flattened, lacking humeral calli and basal impressions, with rounded apices; elytral disc with distinct large and deep punctures arranged in nearly complete longitudinal rows. Base of each elytron with large setiferous punctures (Fig. 41; sp) bearing a long and thickened seta (often broken off in dry-mounted specimens).
Abdomen (Figs 42–43) with sternite III not fused with metaventrite, about as long as sternites IV and V together; sternite VIII in male with rounded posterior margin. Sternite III with indistinct anterolateral (postmetacoxal) impressions filled with leaf-shaped setae.
Aedeagus (illustrated in Castellini (1996) and Jałoszyński et al. (2015, 2018)) symmetrical and lightly sclerotized, strongly elongate, parameres partly fused to lateral walls of median lobe, with apices strongly curved mesad; flagellum simple and broad, not looped. Ejaculatory duct with strongly elongate and narrow sperm pump lacking funnel-like collars.
Spermatheca (Fig. 43) globular and thick-walled, nearly spherical, with small accessory gland.
Sexual dimorphism typically not evident, females can be slightly larger than males. Only in two species (L. orousseti Castellini, 1996 and L. piniphila Franz, 1988) males differ from females in having slightly broader profemora and protibiae, the latter with an apical projection or tooth; rarely the tarsomere I of male is enlarged.
Characteristics. Larva. Body (Fig. 45) campodeiform, subparallel and flattened, whitish with testaceous head, moderately densely covered with thickened setae.
Head prognathous, conspicuously large, broader than thorax, rhomboidal, strongly transverse, broadest near middle; posteriorly head capsule with a short annuliform 'neck'; with one pair of dorsolateral stemmata; epicranial stem and frontal sutures distinct; nasale with two long and broad teeth separated by a deep U-shaped emargination.
Mandibles falciform and strikingly long and slender, much longer than head or antennae, apices pointed, mesal margins smooth; stipital projection of maxilla with two lobes, subapical lobe elongate and densely setose, apical lobe broad and bearing two modified thick setae; maxillary palp long, with all palpomeres elongate, palpomeres II and III comparable in length; labial palpomere II longer than I.
Antenna only slightly longer than head, weakly clubbed, antennomeres I and II each strongly elongate and of similar length, but antennomere II broader than I and slightly broadened distad, broadest near apex; antennomere III small, strongly elongate, shorter than accessory appendage of antennomere II, which is strongly elongate, slightly asymmetrical, subconical and slightly bent near middle.
Thoracic tergites with demarcated tergal plates and distinct ecdysial lines at least on pronotum and mesonotum.
Abdomen with ten segments, all except X transverse; segment X elongate; urogomphi present, each composed of one elongate segment fused with posterolateral margin of abdominal segment IX and bearing several long apical bristles.
Legs long and slender, densely covered with relatively short, spiny setae.
Spiracles annular, lateral, nine pairs: one on mesothorax and eight pairs on abdominal segments I–VIII.
Composition and distribution. Leptomastax comprises 23 species (one with two subspecies) distributed (Fig. 8) mainly in the northern and eastern parts of the Mediterranean Basin, with single species occurring east to the Black Sea and south to the Caspian Sea; in Spain, France, Italy, Croatia, Montenegro, Bosnia & Herzegovina, Serbia, Macedonia, Albania, Bulgaria, Romania, Greece, Turkey, Israel, Jordan, Lebanon, Georgia (Abkhazia) and Iran. Majority of species occur in mountains or highlands and in proximity of the Mediterranean Sea, Black Sea and Caspian Sea coastlines.
Natural history. Leptomastax seems to be adapted to life in deep layers of soil, and its characters are most derived among Leptomastacini. Species of this genus can be collected by sifting the upper organic layers of soil (i.e. leaf litter), but also by the 'soil washing' technique, from mineral layer of soil. They can be found in deciduous forests in moist places (e.g., Figs 52, 55–56), but also in relatively dry habitats, as shrublands, in leaf litter accumulated under bushes (e.g., Figs 53–54).
The extremely long mandibles clearly suggested predatory habits of Leptomastax, although no published records exist supporting this suspicion. I had an opportunity to make observations of three living adults of L. rousi, collected in Romania from the mineral soil layer. Beetles survived a week under laboratory conditions. During that time, they were not observed actively hunting for quickly-moving springtails, mites and other potential prey provided. Most of the time beetles vividly walked around the plaster of Paris arena, penetrating all spaces between particles of soil, rotten wood and mosses, inserting their flat heads and long mandibles into small crevices and pits in the surface of plaster of Paris, and easily climbing smooth plastic walls of the Petri dish. As a vented Petri dish was used, there was a tiny space between the vertical walls of the bottom dish and its lid to allow for air exchange. This space was large enough for beetles to insert the head between the lid and the upper surface of the wall of the bottom dish. This made it possible to make observations from above, through transparent plastic, of what beetles were doing with their heads inserted into this narrow space, providing an analog for similarly narrow spaces between soil particles. The flat head with very long mandibles functioned as a capturing device to detect any objects and drag them out, as long as it was possible to pierce such an object at least with one mandible. The 'probing' of this space (as well as those between other objects on the arena) was performed by beetles for most of the time, and one beetle would walk for hours on the wall of the arena just below the lid, inserting its head into the narrow space, spreading and closing its mandibles for several seconds, then retracing the head, moving one or two millimeters further on, inserting the head and again spreading and closing the mandibles. This behavior was repeated hundreds of times. When small dead isotomid springtails were placed in this space, they were sooner or later detected by one of the beetles on the arena, quickly captured in closing mandibles and pulled out. A successful beetle was observed manipulating the prey with its mandibles and front legs to move the springtail close to the maxillae, and the prey was nearly completely eaten within a few minutes. The space under the lid was even more frequently searched for food than spaces between soil, wood and moss particles on the arena. If wounded, slowlymoving, and often relatively large mesostigmatan mites and isotomid springtails were placed in such narrow crevices or under twigs of moss, they were found, pulled out and eaten in a similar way. Such a large prey (Figs 46– 51), still moving (although not very vigorously), was observed being carried in the mandibles for 15–30 min, the beetle's mandibles were moving, but only slightly spreading and then strongly closing again, pulling the pray close to maxillae and inflicting more damage to the cuticle, which presumably facilitated penetration of prey's tissues by digestive juices. Living springtails and mesostigmatan mites of various sizes, when touched by beetles, were able to quickly escape and were not seen being captured even once during the one-week observation period.
Although the above observations are only preliminary, they are valuable as representing the first record of feeding-related behavior of any member of Leptomastacini. It seems that Leptomastax uses a complicated threedimensional system of narrow spaces between soil particles to search for food, and its searching technique relies on many repeated insertions of its flat head into small crevices, where potential prey may hide, spreading and closing its enormously long, slender and curved mandibles, and, if a springtail or other invertebrate has been found, it is then momentarily pierced and pulled out of its shelter. In natural conditions, even a large, strong and fast-moving prey may probably be captured, if there is no space to jump or run. The very flat head and the very long and strongly curved mandibles form a perfect long-reach tool to probe narrow spaces, the slender and sharp mandibular apices pierce through prey's cuticle quickly, and closing, overlapping curved mandibles prevent a wounded prey from freeing itself from this firm grip. Moreover, the pair of long setae on the vertex of Leptomastax seems to function as tactile sensors, informing the beetle how deep it can insert its head into a crevice, as inserting the anterior body too deep could impede the function of front legs and slow down the process of retracting mandibles with a large and resisting prey. The unusually broad separation between mandibular bases, yet increased by the grotesquely broadened head, has a functional explanation. If the mandibles were similarly long (to allow for a long reach) but with narrowly separated bases, it would be impossible for the beetle to eat its prey while still held with mandibular apices. But when broadly separated and strongly curved mandibles are being closed, with their tips sunken into the prey's body, a springtail or mite is quickly pierced through and moved close to maxillae and the mouth opening, which increases damage to its cuticle and at the same time brings it into the range of digestive juices exuded from the beetle's mouth.
As the larva of Leptomastax has a very similar shape of mandibles and head as adults, it seems possible that it also feeds in a similar way.
Remarks. As reviewed and clarified by Castellini (1996), the grammatical gender of the name Leptomastax was problematic for several authors, and the name of the type species of the genus, L. hypogea, was several times emended to become masculine or neuter in grammatical gender, often gaining an additional "a" after "g". Even Pirazzoli, who described this species as L. hypogeum, labeled a box with his specimens " hypogaeus mihi" (Castellini 1996). In fact, the Greek stem " mastax " (mouth) is feminine. In Leptomastax this stem is combined with the prefix derived from the Greek leptos (thin), and clearly refers to the slender mandibles.
Morphological structures of Leptomastax were described and illustrated by Castellini (1996), but this author used a rather unorthodox Italian terminology, not always congruent with standard morphological terms used by other coleopterists. Moreover, some structures were either omitted or misinterpreted. The head in dorsal view was shown with a pair of dorsal tentorial pits ("fosetta tentoriale") (Castellini 1996, fig. 2), whereas in fact there are no such pits. Because of the typically light pigmentation, the sites of fusion of dorsal tentorial arms with the head capsule can be seen through the cuticle as a pair of dark dots (similarly darkened insertions of dorsal tentorial arms are illustrated in a transparent mount of Taurablepton in Fig. 69; idta), which in dry-mounted specimens and in transparent mounts may be easily confused with tentorial pits. SEM examination demonstrates clearly that the vertex has not even traces of tentorial pits (Fig. 29). The hypostomal ridges were misinterpreted as sutures (Castellini 1996, fig. 3); the posterior tentorial pits were illustrated as circular (Castellini 1996, fig. 3), whereas in fact in Leptomastax the pits are developed as narrow, long and typically arcuate 'slots'. The stipes was illustrated as a structure composed of basistipes and palpifer completely and indistinguishably fused together (Castellini 1996, figs. 3, 9), whereas in all Scydmaeninae, including Leptomastax, the subtriangular basistipes is sharply demarcated from surrounding structures by sutures well-visible not only under SEM, but also in transparent mounts under light microscope. Details of meso- and metaventrite were simplified (Castellini 1996, fig. 13), and the conspicuous metaventral foveae filled with strongly modified, leaf-like setae, were not illustrated at all.
Leptomastax was comprehensively revised by Castellini (1996), with accurate illustrations of aedeagi and an identification key. However, one species and one subspecies proposed by other authors seem to have been described insufficiently to allow for unambiguous identification. Leptomastax vlascensis (Karaman, 1962) was described on the basis of a single female and this species was omitted from the identification key given by Castellini (1996). Leptomastax mehadiensis cisdanubiensis Nonveiller & Pavičevič, 2002 was differentiated from the nominotypical subspecies on the basis of minor external characters, and the authors stated that aedeagi of both subspecies show no differences. These taxa require further study to verify their separate placement.
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 20-30, DOI: 10.11646/zootaxa.4453.1.1, http://zenodo.org/record/1454920