Plesioxylion, Liu & Beaver, 2023

Liu, Lan-Yu & Beaver, Roger A., 2023, A new West African genus of Bostrichidae (Coleoptera), and a key to the Afrotropical genera of tribe Xyloperthini, European Journal of Taxonomy 885 (1), pp. 21-32 : 22-27

Genus Plesioxylion gen. nov.

urn:lsid:zoobank.org:act:681AF627-03D5-4662-93C5-46E3052BD34A

Type species

Amintinus gambianus Borowski, 2018 .

Diagnosis

A member of the tribe Xyloperthini characterized by the antennal club segments elongated, the mandibles crossed at the tips, and the lamelliform intercoxal process of the first abdominal ventrite ( Lesne 1901; Fisher 1950; Liu & Schönitzer 2011). The new genus is distinguished from other genera of Xyloperthini by the following combination of characters: frons weakly convex, without long upwardly directed hairs on the head in either sex. Mandibles symmetrical, sharply pointed. Antenna with ten antennomeres, including a 5-segmented funicle and 3-segmented club, antennomeres of club lacking stiff, erect hairs, without clear sensory maculae; antero-lateral angle of pronotum with a moderately strong recurved uncinate tooth, pronotum without a lateral carina; posterior part of elytral disc without costae or teeth, elytral declivity obliquely sloping, simple in male, female with a broadly truncate emargination in middle one-third of posterior margin; 5 th abdominal ventrite of male with pleural pieces swollen towards midline of posterior margin; 4 th abdominal ventrite of female with long, thick, golden hairs on anterior part of median impression, and 5 th abdominal ventrite strongly emarginate in middle.

Etymology

The genus name means ‘near’ (Greek: ‘πλησίον’) the genus Xylion .

Description

Male ( Figs 1–2 )

MEASUREMENTS. 2.4‒3.2 mm long, about 2.9–3.1× as long as wide.

COLORATION. Dark brown to black with the antennae, palps, femora, tibiae except for protibiae yellowish-brown. Coxae and protibiae brown. Posterior part of last abdominal ventrite and pleural pieces yellowish-brown.

HEAD ( Fig. 1B‒C ). Moderately convex. Frons longitudinally rugose with sparse, semi-erect, short hairlike setae, except shiny and impunctate in narrow median area, and immediately above fronto-clypeal suture. Clypeus granulate, anterior margin weakly emarginate with short erect hairlike setae. Labrum shiny and punctate. Eyes of moderate size, clearly separated from the genae posteriorly. Antennae 10-segmented, scape elongate, 2 nd antennomere slightly shorter than scape; 3–7 antennomeres together distinctly longer than the last club antennomere in length. Club antennomeres without sensory maculae, with sparse erect hairlike setae on the anterior face of 8 th and 9 th antennomeres.

PRONOTUM ( Fig. 1A‒C ). As long as wide to slightly wider than long, sides evenly curved in basal two-thirds, narrowing anteriorly; anterior angle with a moderately strong recurved uncinate tooth; anterior margin strongly, slightly angularly emarginate between the anterior teeth. Anterior slope rugose above margin without distinct asperities, sparse punctures between the rugosities; upper part of anterior slope to summit with small, slightly transverse asperities more or less concentrically arranged. Posterior angles rounded without lateral carinae. Pronotal disc mostly shiny, smooth; coarsely granulate-punctate in middle behind summit; punctures smaller and sparser posteriorly, fine and very sparse on sides; punctures with short, whitish, semi-appressed hairlike setae.

SCUTELLUM. Small, tuberculiform.

ELYTRA ( Fig. 1A, C‒D ). 1.8–1.9× as long as wide, slightly narrower than pronotum at base, widening slightly towards apex. Parallel-sided, moderately shiny. Basal margin of elytra with a short carina on each side of scutellum. Disc densely, moderately finely granulate-punctate dorsally, the sides more sparsely punctured except close to elytral declivity. Declivity steep, obliquely truncate, its lateral margin raised and costate except on upper margin, the punctures denser and coarser than on dorsal surface; suture swollen on upper two-thirds of declivity and coarsely punctured; a weak impression on each side of suture. Elytral apices separated by a V-shaped emargination. Vestiture of short, whitish, recumbent hairlike setae, longer, yellower and denser on declivity.

LEGS. Protibiae parallel-sided without teeth on external side. Long hairlike setae on inner side of all tibiae, and on ventral surface of tarsi.

ABDOMEN ( Figs 1C‒D , 2E ). Ventrites 1–4 almost equal in length, their posterior margins straight; shiny, finely, rather sparsely punctured with short, recumbent, whitish hairlike setae. 5 th ventrite with posterior margin evenly rounded except in middle where concave, the concavity with dense, short yellowish hairlike setae; pleural pieces rather swollen towards midline, densely setose.

AEDEAGUS ( Fig. 2B‒D ). Penis elongate, cylindrical with expanded apex. Basal pieces droplet-like, sharply pointed apically. Parameres narrowed at base where attached to stout, thick muscles, broadened in middle part with a short lateral lobe, apex finger-like with rounded tip.

Female ( Figs 3–4 )

MEASUREMENT. 3.0 mm long, 2.8–3.0× as long as wide.

COLORATION. Reddish brown with the antennae, palps, coxae, femora, tibiae, except for protibiae, yellowish-brown. Protibiae brown.

HEAD. Generally as in male, but median shiny area above fronto-clypeal suture reduced.

PRONOTUM ( Fig. 3A, C ). Generally as in male, but emargination of anterior margin between teeth on anterior angles shallower, and more evenly curved; pronotal disc behind summit smoother and more shiny, with sparse punctures, becoming smaller and sparser posteriorly.

SCUTELLUM. As in male.

ELYTRA ( Figs 3C, E , 4A ). Elytral disc and sides generally as in male. Upper margin of declivity indistinct, slightly longitudinally impressed next to suture, broadly convex on each side beyond the impressions. Declivity very deeply, very widely emarginate ( Fig. 4A ), its lateral margins raised and costate, the surface shiny, weakly convex, coarsely granulate-punctate on upper part, punctures sparser and finer, and granules weaker towards apex, apical angles moderately acute ( Figs 3E , 4A ); truncated emargination on middle of posterior margin filled by a pair of spatulate processes ending in very elongate, needle-like tips extending well beyond elytral apices ( Figs 3E , 4A ). Vestiture of disc similar to male, declivity with longer, yellowish hairs on upper part, shorter and sparse apically; processes glabrous.

LEGS. Similar to male but protibiae with a row of teeth on the external side.

ABDOMEN ( Fig. 3B, D ). Ventrites 1‒3 almost equal in length, posterior margin straight; 4 th ventrite slightly shorter with a strongly concave median area posteriorly; just anterior to this a thick brush of golden hairs ( Fig. 3D ), more than twice as long as ventrite; 5 th ventrite strongly concave with a broadly concave apical margin fringed by dense golden hairlike setae. Ventrites shiny, finely, rather sparsely punctured with short, recumbent, whitish hairlike setae.

OVIPOSITOR. Similar to other genera of bostrichids ( Lesne 1924), narrow, very elongate, pointed with a pair of short palpiform appendages at apex, adapted for piercing wood.

Figures

Fig. 1. Plesioxylion gambianus (Borowski, 2018) gen. et comb. nov., ♂ (RBINS beside C in LYL). A. Dorsal view. B. Front view of head and pronotum. C. Lateral view. D. Posterior view of elytral declivity. E. Ventral view. Scale bar: A, C, E = 1 mm; B, D = 0.75 mm.

Fig. 2. Plesioxylion gambianus (Borowski, 2018) gen. et comb. nov., ♂. Last visible abdominal segment and aedeagus. A. Ventral view of last tergite.B. Posterior view of aedeagus. C. Ventral view of aedeagus. D. Dorsal view of aedeagus. E. Rear view of last ventrite. Abbreviations: b = basal piece; p = paramere (refer to Lesne 1940).

Fig. 3. Plesioxylion gambianus (Borowski, 2018) gen. et comb. nov., ♀ (LYL). A. Dorsal view. B. Ventral view. C. Lateral view. D. Ventral view of abdominal ventrites. E. Postero-lateral view of elytral declivity. Scale bar: A–C = 1 mm; D–E = 0.75 mm.

Fig. 4. Declivity of female of the representatives of selected genera. A. Plesioxylion gambianus (Borowski, 2018) gen. et comb. nov.B. Mesoxylion collaris(Erichson, 1842). C. Amintinus minutissimus Damoiseau, 1968. D. Xylion securifer Lesne, 1901.