Elytrobium, Assing, 2013

Assing, Volker, 2013, Two new genera of Lathrobiina from the East Palaearctic region (Coleoptera: Staphylinidae: Paederinae), Beiträge Zur Entomologie = Contributions to Entomology 63 (2), pp. 219-239 : 221-222

Elytrobium gen. n.

Type species: Lathrobium monilicorne SHARP, 1889

Etymology:

The name (gender: neuter) is composed of the Greek word elytron and the ending of the generic name Lathrobium . It alludes to the long elytra combined with a habitus somewhat resembling species of Lathrobium .

Description:

Species of relatively small to moderate size; body length 5.2-7.8 mm; length of forebody 3.0-4.0 mm. Habitus as in Figs 1, 7 , 14, 22 . Coloration dark, body usually black, rarely dark-brown; legs and antennae at least partly paler.

Head (e.g., Figs 2, 8 , 15, 23 ) rather small in relation to body and slender, oblong, mostly broadest across eyes, and more or less distinctly tapering behind eyes; posterior angles rounded, noticeable or obsolete; neck approximately half the width of head; punctation on dorsal surface distinct; interstices with microreticulation; ventral aspect ( Fig. 32 ) strongly, rugosely sculptured, matt, and with shallow punctures; gular sutures broadly separated; genal carinae absent. Eyes convex, composed of numerous fine ommatidia, and at least as long as half distance from posterior margin of eye to neck. Antenna ( Figs 16, 24 , 47 ) moderately slender; antennomeres V-X about as long as broad or weakly oblong. Maxillary palpomere III of variable morphology, slender to conspicuously dilated, 2.0-3.5 times as long as broad. Labial palpus ( Fig. 42 ) short, with weakly oblong palpomeres I and II, and with relatively short palpomere III. Mandibles ( Fig. 40 ) as in Lathrobium . Labrum ( Fig. 41 ) distinctly, but not very deeply bilobed.

Pronotum (e.g., Figs 2, 8 , 15, 23 ) moderately oblong, mostly widest in posterior half, broader than head, and strongly convex in cross-section; posterior angles weakly marked; punctation distinct and dense; impunctate midline narrow; interstices with or without microsculpture. Prosternal process long and very acute.

Elytra (e.g., Figs 2, 8 , 15, 23 ) conspicuously long and broad in relation to pronotum; supramarginal line absent; punctation distinct, irregular or arranged in indistinct series. Hind wings fully developed. Ventral aspect of meso- and metathorax as in Lathrobium . Protarsomeres I-IV distinctly dilated in both sexes. Metatarsomere I approximately as long as II.

Abdomen narrower than elytra; punctation dense and distinct on anterior tergites, gradually becoming finer and sparser towards the abdominal apex; tergite VII with palisade fringe; tergite VIII without sexual dimorphism and with truncate posterior margin; sternite III with long and pronounced median keel extending over the full length of sternite; sternites III-VI without sexual dimorphism; tergites IX and X without sexual dimorphism, tergite IX long, slender, and undivided in the middle, postero-lateral processes apically with spine-like process ( Fig. 39 ); tergite X small, much shorter than antero-median portion of tergite IX ( Fig. 39 ).

: sternite VII (e.g., Figs 3, 9 , 17, 25 ) weakly modified, without distinct impression and with unmodified pubescence; sternite VIII (e.g., Figs 4, 10 , 18, 26 ) with shallow posterior excision, otherwise unmodified; sternite IX ( Figs 11 , 19, 27 , 35 , 50 ) symmetric and anteriorly acute; aedeagus ( Figs 5-6, 12-13 , 20-21, 28-29 , 36-37 , 51-55 ) small in relation to body and distinctly asymmetric; ventral process somewhat twisted, with the right margin projecting ventrad and the left margin dorsad in ventral view, subapically curved, and apically usually more or less distinctly hooked in lateral view; dorsal plate weakly sclerotized, narrow, and lamellate; internal sac devoid of sclerotized structures; parameres absent.

: sternite VIII with convex posterior margin, posterior portion with micropubescence ( Figs 56-57 ).

Comparative notes:

Among the Lathrobiina , the new genus is readily identified by external characters alone, particularly the small, oblong, distinctly microsculptured, and posteriorly more or less distinctly tapering head combined with dark coloration, and long elytra. In addition, it is characterized by weakly modified male sternites VII and VIII, as well as by a distinctive shape of the aedeagus without sclerotized internal structures.

Among the genera currently attributed to the Lathrobiina, Elytrobium has some resemblance only to Lathrobium and some genera treated as subgenera of Lathrobium until several decades ago, in particular Tetartopeus and Lobrathium . Aside from the characters pointed out above, Elytrobium differs from the latter by the absence of a supramarginal line of the elytra. Regarding its head shape, Elytrobium is most similar to Tetartopeus , from which it is distinguished by the broader neck ( Tetartopeus : neck distinctly less than half the width of head), by the completely different secondary sexual characters in both sexes, and by the completely different morphology of the aedeagus ( Tetartopeus : aedeagus symmetric, with long, slender, and apically acute ventral process, with distinctly larger and more sclerotized dorsal plate, and with dark internal structures). For illustrations of Tetartopeus see ASSING (2009, 2011).

Using the key to paederine genera in COIFFAIT (1982), Elytrobium would key out together with Lathrobium , the most speciose of all genera of Lathrobiina . Based on revisionary studies of Lathrobium from both the West and the East Palaearctic region, it is concluded that Elytrobium represents a distinct lineage. Despite a slight resemblance with some macropterous Lathrobium species , Elytrobium differs morphologically in numerous and significant respects: head smaller and posteriorly usually tapering; ventral aspect of head conspicuously sculptured and with broadly separated gular sutures; labrum less deeply bilobed; labial palpus shorter and with less oblong palpomeres; pronotum of different shape ( Lathrobium : pronotum with subparallel lateral margins or widest in anterior half); prosternal process longer and more acute; elytra conspicuously long; median keel of sternite III long; absence of a sexual dimorphism of tergites VIII-X; male sternites VII and VIII weakly modified; morphology of the aedeagus characteristic, internal structures absent. For illustrations of the labrum and the labium of the type species of Lathrobium , L. elongatum (LINNAEUS, 1767) , see Figs 43-44 . In all the previously revised Lathrobium species the abdominal tergites IX and X are subject to a pronounced sexual dimorphism, most likely one of the main synapomorphies constituting the monophyly of the genus. In some species (groups) the aedeagus may be of highly derived morphology and lack internal structures. Likewise, some species (groups) have weakly modified male sternites VII and VIII. These conditions, however, undoubtedly represent secondary reductions and are not homologous to the condition in Elytrobium . Moreover, the male sternite IX in Lathrobium is mostly less acute anteriorly and more or less asymmetric, particularly so in species with an asymmetric aedeagus. Finally, the available data suggest that Elytrobium differs from Lathrobium also regarding its natural history. The vast majority of Lathrobium species inhabits the leaf litter layer of shrub and forest habitats or lives epigeically in unforested habitats such a lake shores, river banks, and arable land. However, the genus also includes numerous microphthalmous or anophthalmous, micropterous, and depigmented species with a hypogean habitat. For notes on Elytrobium see the following section.

Distribution and natural history:

The currently known distribution of Elytrobium is confined to the East Palaearctic: China, Taiwan, and Japan ( Map 1 ). All the species of this genus have long elytra, fully developed hind wings, and are probably capable of flight. Nevertheless, they have been found only on very rare occasions. Except for E. monilicorne (two specimens), no more than one specimen was found in one locality, and three of the six species are represented only by singletons. These observations suggest that the Elytrobium species inhabit a special, cryptic habitat and are recorded only by coincidence. The specimens collected by Aleš Smetana (three species) were found in moss, leaf litter, and vegetation in moist to wet habitats, one was captured with a yellow pan trap.

Figures

Map 1: Distribution of Elytrobium gen. n. in the southeastern East Palaearctic region: E. gongganum sp. n. (open circle); E. qinlinganum sp. n. (open triangle); E. scindens sp. n. (filled diamonds); E. seminitidum sp. n. (open diamond); E. alesianum sp. n. (filled circles); E. monilicorne (SHARP) (filled triangle).

Figs 1-13: Elytrobium monilicorne (SHARP) (lectotype) (1-6) and E. gongganum sp. n. (7-13): habitus (1, 7); forebody (2, 8); male sternite VII (3, 9); male sternite VIII (4, 10); aedeagus in lateral and in ventral view (5-6, 12-13); male sternite IX (11). Scale bars: 1-2, 7-8: 1.0 mm; 3-4, 9-10: 0.5 mm; 5-6, 11-13: 0.2 mm.

Figs 14-29: Elytrobium qinlinganum sp. n. (14-21) and E. seminitidum sp. n. (22-29): habitus (14, 22); forebody (15, 23); antenna (16, 24); male sternite VII (17, 25); male sternite VIII (18, 26); male sternite IX (19, 27); aedeagus in lateral and in ventral view (20-21, 28-29). Scale bars: 14-15, 22-23: 1.0 mm; 16-18, 24-26: 0.5 mm; 19-21, 27-29: 0.2 mm.

Figs 30-44: Elytrobium scindens sp. n. (30-42) and Lathrobium elongatum (LINNAEUS) (43-44): habitus (30); forebody (31); median portion of ventral aspect of head (32); male sternite VII (33); male sternite VIII (34); male sternite IX (35); aedeagus in lateral and in ventral view (36-37); female sternite VIII (38); female tergites IX-X (39); right mandible (40); labrum (41, 43); labium (42, 44). Scale bars: 30-31: 1.0 mm; 33-34, 38-39: 0.5 mm; 32, 35-37, 40: 0.2 mm; 41-44: 0.1 mm.

Figs 45-57: Elytrobium alesianum sp.n. (45-53: holotype): habitus (45); forebody (46); antenna (47); male sternite VII (48); male sternite VIII (49); male sternite IX (50); aedeagus in lateral and in ventral view (51-52, 54-55); apical portion of ventral process of aedeagus in ventral view (53); female sternite VIII (56); postero-median portion of female sternite VIII (57). Scale bars: 45-46: 1.0 mm; 47-49, 56: 0.5 mm; 50-55, 57: 0.2 mm.