Silvanolomus depressus, Halstead, 2012

Halstead, David G. H., 2012, New species of Oryzaephilus and Silvanolomus from Socotra Island (Coleoptera: Silvanidae: Silvaninae), Acta Entomologica Musei Nationalis Pragae 52, pp. 223-231 : 228-230

Silvanolomus depressus sp. nov.

( Figs. 2 , 8–11 )

Type locality. Yemen, Socotra Island, Dixam plateau, Firmihin ( Dracaena forest), 12°28.6′N, 54°01.1′E, 490 m.

Type material. HOLOTYPE: dissected J ( NMPC): ‘ YEMEN, SOCOTRA Island / Dixam plateau Firmihin ( Dracaena forest) / 12°28.6′N, 54°01.1′E, 490m. / J. Bezděk leg., 15-16.xi.2010 ’. PARATYPE: 1 dissected ♀, with the same data as holotype ( NMPC).

Description (measurements/ratios given for holotype first): Body. Brown, vertex of head and disc of pronotum appearing flat. Length 2.0 mm, 2.2 mm; length: maximum elytral breadth ratios, 30.74: 10, 29.7: 10. Pubescence golden.

Head. Length: breadth across eyes ratios, 10: 13.75, 10: 14.37; eyes very large and protuberant (as usual in the genus), separated across mid-line by ×4.8, ×5.0 breadth, length: breadth ratio 23.1: 10, 24.62: 10; antennal length about 1/3 body length; vertex almost flat, with puncturation coarsely reticulate.

Pronotum. Length: maximum breadth ratio, 11.81: 10, 11.02: 10 i.e., slightly more elongate in male than in female seen (although possibly significant, similar sexual difference has not been observed in other Silvanolomus – more material is required for confirmation); puncturation as on vertex of head, coarsely reticulate; disc overall shallowly depressed (appearing almost flat at low magnification), depression deepest toward base; lateral margins with teeth obsolete, represented by six very small prominences (anterior and posterior angles included), most obvious in larger (female) specimen, coarse punctures at pronotal edge producing an uneven margin between prominences.

Elytra. Slightly less than ×2 as long as broad, length: maximum breadth ratios, 18.4: 10, 18.1: 10; interstriae with setae arranged in alternate single and double rows, one row on 1 st (sutural) interstriae, two on 2 nd etc.

Male genitalia ( Figs. 10–11 ). Internal sac as in Fig. 10 , usual form in Silvanolomus , rows of 11–13 obvious rods on each side towards ostium; median lobe somewhat triangular, apex rounded, row of setae across basal half; parameres, at about apical third tapered from distal margin to apex, bearing 5–6 long setae along apical margin, longest more than half as long as parameres, few short setae on distal half at beginning of taper.

Differential diagnosis. This species differs from other described and new ones known to the author in having the pronotal disc shallowly depressed and appearing rather flat, and the head with the vertex comparatively flat. Other species have the pronotum and head obviously, transversely, moderately convex.

Poorly developed pronotal teeth, although somewhat variable, are also a characteristic of S. inermis ( Japan, China and Korea). In addition, this species has similar genitalia but they differ from those of the new species as follows: the median lobe appears more triangular (sides straighter) and the parameres more widely separated, more parallel sided and with the point of taper a little closer to the apex (cf. Figs. 11–12 ). Relatively poorly developed teeth are also present on the pronotum of S. pullus (distribution Africa and South Yemen) but teeth in this species are generally more easily distinguished from the smaller prominences between them. The male genitalia of S. depressus sp. nov. and S. pullus do not appear to differ in any significant way, suggesting that they are very closely related. However, separate species status has been given to the taxon based principally on the rather unique character provided by the shallowly depressed pronotal disc.

Etymology. The name refers to the pronotal disc.

Distribution. So far known only from the type locality in Socotra Island.

Figures

Figs.1–2. Habitus, dorsal view. 1 – Oryzaephilus socotraensis sp. nov. (paratype, male); 2 – Silvanolomus depressus sp. nov. (holotype, male).

Figs. 8–12. Silvanolomus spp. 8–11 – S. depressus sp. nov.: 8 – head, pronotum and elytra of male; 9 – pronotum of female; 10–11 – male genitalia, 10 – internal sac, 11 – genitalia without sac. 12 – S. inermis (Reitter, 1876), median lobe and parameres of male genitalia. Scale bars = 1 mm (Figs. 8–9), 0.1 mm (Figs. 10–12).