Plagiophorus ishigachiensis sp. nov.

(Figs 2, 14–21, 28–33, 34)

Type material. Holotype: JAPAN (Okinawa Pref.): ♂, two labels: “ JAPAN, OKINAWA Pref. / Ishigaki Is., Mt. OMOTO/ 20 IX 2003 / leg. P. Jałoszyński ” [white, printed], “ PLAGIOPHORUS / ishigachiensis m. / P. Jałoszyński, 2026/ HOLOTYPUS ” [red, printed] (NSMT). Paratypes (3 exx.): 1 ♂, same data as for holotype; 2 ♀♀, “ JAPAN, OKINAWA Pref. / Ishigaki Is., Mt. OMOTO/ 17 IX 2003 / leg. P. Jałoszyński ” [white, printed]. All paratypes with yellow “ PARATYPUS ” labels, deposited at cPJ, NSMT.

Diagnosis. Male with antennae composed of nine antennomeres, two of them (3 and 4) fused together but with circumferential sulcus marking fusion line; terminal antennomere subtriangular with rounded sides, about as wide as long and as wide as head, with dorsal cavity bean-shaped and with row of thick and dense setae on dorsal surface; eye irregular in shape, with five ommatidia; legs unmodified; metaventrite lacking longitudinal ridges, impressed at middle; exposed portion of abdomen in dorsal view much longer than elytra; abdominal composite ventrite with large median elongate impression, its surface smooth; each elytron with two antebasal foveae; aedeagus twisted in a complex way, basal capsule, distal projections and parameres all strongly asymmetrical.

Description. Body of male (Fig. 2) elongate, strongly convex, dark brown with umbra hue, tarsi slightly lighter, setae distinctly lighter than cuticle, almost entire body surface reticulate, with isodiametric meshes, each cell of mesh with centrally situated seta inserted on minute tubercle; BL 1.43–1.50 mm.

Head (Figs 14–17) in dorsal view pear-shaped, dorsally flattened, broadest at eyes, HL 0.30–0.33 mm, HW 0.28–0.30 mm. Frontovertexal region anteriorly weakly concave, laterally strongly concave anterior to eyes, postocular region laterally convex and strongly narrowing toward occipital constriction; eyes not projecting from head outline (Fig. 17), each with five corneal lenses arranged in elongate cluster. Ventrally (Fig. 15) genal regions strongly expanded mesad so that posterior region of submentum is indiscernible, each gena divided into large anterior and posterior impression. Dorsum of head uniformly sculptured, with regular meshes and sparse, short, suberect setae, ventral surface within genal impressions covered with much finer microsculpture. Antennae (Figs 2, 14–16, 18) about as long as head and pronotum combined; AnL 0.50–0.53 mm; scape slightly less than twice as long as wide, pedicel slightly narrower than scape and distinctly transverse, flagellum composed of seven antennomeres, of which 3 and 4 are fused together but sulcus marks fusion line, antennomeres 3–6 as wide as pedicel, antennomere 7 short and asymmetrical, 8 large, asymmetrical, flat and adpressed against base of terminal antennomere 9, which is subtriangular with rounded sides, convex ventrally and with large dorsal bean-shaped cavity, its interior smooth and asetose, lacking peculiar structures visible in dorsal view, dorsal surface of antennomere 9 with short row of long and thick setae along mesal margin of dorsal cavity. Antennae covered with moderately dense, short and suberect setae, distal margin of terminal antennomere with erect setae as long as those on its remaining convex surfaces.

Prothorax (Figs 14, 15) convex dorsally and flattened ventrally, round in dorsal view. Pronotum (Fig. 14) broadest slightly anterior to middle; PL 0.30–0.33 mm, PW 0.33–0.35 mm. All margins rounded (anterior and posterior ones weakly so), anterior and posterior corners rounded off. Lateral antebasal foveae minute and barely discernible, distant from posterior pronotal margin. Disc with sculpture and setae similar as on dorsum of head, prosternum with finer meshes.

Elytra (Fig. 14) together subtrapezoidal with strongly rounded sides, broadest indistinctly behind middle; EL 0.35–0.38 mm, EW 0.45–0.51 mm. Each elytron with two antebasal foveae; disc with broad, shallow and diffuse longitudinal impression extending from outer fovea to about middle of elytron. Elytral surface with meshes and setae similar as those on head and pronotum.

Mesoventrite (Fig. 15) with sharply marked transverse impression on prepectus, remaining regions covered with meshes as fine as those on ventral surface of head.

Metaventrite (Fig. 15) between meso- and metacoxae lacking ridges, weakly impressed, impressed area posteriorly with indistinct microsculpture; regions laterad coxae with large meshes (Fig. 19).

Legs (Figs 2, 15, 16) moderately long and slender, unmodified.

Abdomen (Figs 14, 15) in dorsal view with only one composite tergite exposed, distinctly longer than elytra, semioval, AbdL 0.48 mm, AbdW 0.44–0.50 mm, dorsal surface with sculpture and setae similar to those on elytra. Tergite VIII visible in ventral view (Figs 15, 33), its exposed portion subtriangular with nearly straight lateral margins. Large composite ventrite with elongate median impression, its surface lacking sculpture, glossy. Sternite VIII exposed as short and wide stripe (Fig. 15), disarticulated sternite VIII (Fig. 32) is distally weakly bisinuate and bears small weakly sclerotized median anterior lobe between long lateral apodemes.

Aedeagus (Figs 28–31) elongate, AeL 0.25 mm, strongly twisted, so that it is difficult to identify dorsal and ventral faces, basal capsule, distal projections and parameres all strongly asymmetrical, basal capsule with oval diaphragm, short distal projection forming oval lobe, long distal projection curved and with slender rod-like process at broadened apex.

Female. Externally differs from male in distinctly smaller terminal antennomeres lacking dorsal cavities (Fig. 18), smaller eyes, each with only two corneal lenses (Fig. 21), and median region of composite abdominal ventrite with proximal flattening covered with similar reticulation as remaining surface of abdomen. BL 1.53–1.58 mm; HL 0.28–0.33 mm, HW 0.30 mm, AnL 0.40–0.45 mm; PL 0.33–0.35 mm, PW 0.35 mm; EL 0.38 mm, EW 0.50–0.53 mm; AbdL 0.53–0.55 mm, AbdW 0.50–0.51 mm.

Distribution. Ishigaki Island, Yaeyama Archipelago, Ryukyu, Japan.

Etymology. The adjective ishigachiensis is derived from the word ‘Ishigachi’, meaning Ishigaki in the Uchinaaguchi language.

Remarks. All specimens were sifted from rotten wood inside a hollow base of a standing old deciduous tree (Fig. 34), together with Plagiophorus hispidus.

Plagiophorus ishigachiensis sp. nov. can be easily distinguished from its Japanese relatives by the body shape, male secondary sexual characters and the aedeagus. The aedeagus is strongly twisted, so that it is difficult to identify dorsal and ventral surfaces, and is similar to the geographically close Chinese P. grandoculatus Sugaya, Nomura & Burckhardt, 2004. However, the males of P. ishigachiensis have much smaller eyes, each with only five corneal lenses (~40 facets in P. grandoculatus), a row of thick setae at the rim of the dorsal cavity in the terminal antennomere (lacking in P. grandoculatus), and lack the paired setal patches on the metaventrite (“setigerous patches” of Sugaya et al. 2004)). The lack of the latter character excludes P. ishigachiensis from the P. hispidus group of Sugaya et al. 2004). Males of the sympatric P. hispidus (collected together with specimens of P. ishigachiensis during the present study) clearly differ from P. ishigachiensis in the following characters: (1) antenna composed of 8 antennomeres (9 in P. ishigachiensis, with the annulate antennomere 3 tightly adhering to 4 and a shallow sulcus separating them); (2) terminal antennomere semioval, clearly wider than long (in P. ishigachiensis subtriangular and about as long as wide); (3) dorsal cavity of terminal antennomere suboval (bean-shaped in P. ishigachiensis, with a subtriangular lobe on its distal margin); (4) margin of dorsal cavity of the terminal antennomere lacking a group of densely set thick setae directed towards the cavity (present in P. ishigachiensis); (5) the bottom of dorsal cavity of the terminal antennomere with two well-defined sensory or glandular fields (function unclear) and a longitudinal ‘stria’ (all lacking in P. ishigachiensis); (6) eye with 2–4 facets (5 in P. ishigachiensis); a single basal elytral fovea (two on each elytron in P. ishigachiensis); (7) exposed region of the abdomen in dorsal view about as long as wide (distinctly elongate in P. ishigachiensis); (8) pro- and mesotibiae each with a subapical denticle (lacking in P. ishigachiensis); (9) a pair of setal patches on the metaventrite (lacking in P. ishigachiensis); and (10) the median area of the composite abdominal ventrite weakly impressed, not elongate, asetose at middle (in P. ishigachiensis the median area of the composite abdominal ventrite is strongly impressed, strongly elongate, setose at middle).