Airaphilus abei, Yoshida & Halstead & Hirowatari, 2019

Yoshida, Takahiro, Halstead, David G. H. & Hirowatari, Toshiya, 2019, Discovery of the genus Airaphilus (Coleoptera: Silvanidae) in Japan, with a description of a potentially endangered new species, Acta Entomologica Musei Nationalis Pragae (Acta. Ent. Mus. Natl. Pragae) 59 (1), pp. 211-216 : 212-215

Airaphilus abei sp. nov.

[Japanese name: Hyoutan-hoso-hiratamushi]

( Figs 1–3 )

Type material. HOLOTYPE: ♁, Kokeyachi bog, Tsugaru City, Aomori Prefecture, Japan, 5. V. 1992, Azuma Abe leg. ( EUMJ) . PARATYPES: 1♀ and 2 unsexed specimens, same data as ( EUMJ); 1 unsexed specimen, ABE76-373 [the label data is missing], Azuma Abe leg. ( SEHU).

Description. Habitus ( Fig. 1 ). BL: 2.77–3.36 mm (n = 4). Surface dark brown except for reddish brown antennae, legs, elytra and distal abdominal ventrites; setae golden.

Head ( Figs 1 , 2A ). Subquadrate, slightly shorter than wide, HL 0.43–0.49 mm, HW 0.50–0.56 mm, HW/HL 1.10–1.22; IE/HL 0.72–0.80 (n = 4); genal region (front of eyes) a little enlarged laterally, frontal region with paired yellowish setae; temples very short. Eyes moderate in size, strongly protruding, longer than length of antennomere I. Punctation sparse and shallow, consisting of punctures of various sizes, interspaces between punctures with reticulate microsculpture. Pubescence thick and short, ventrally composed of thinner setae, directed toward posterior. Labrum completely covered by clypeus. Antennae ( Fig. 2A ) very long (about half as long as body), with trimerous club; antennomere XI asymmetric, outer side somewhat concave; all antennomeres densely covered with thin, short and semi-elect pubescence plus some thin, longer erect setae; antennal total length and antennomere approximate length ratios from base to apex, both for the holotype, 1.35 mm; 1.6: 1.2: 1.3: 1.1: 1.1: 1.1: 1.1: 1.0: 1.2: 1.1: 1.8.

Pronotum ( Fig. 1 ) longitudinally oval, gradually narrowed towards anterior and posterior margins, widest slightly anterior to middle; anterior margin width almost equal to (not exceeding) head width across eyes, PL 0.67–0.81 mm, PW 0.58–0.72 mm, PL/PW 1.12–1.16 (n = 4); lateral margins with about 12 small teeth at regular intervals, each bearing a short thick seta; anterior margin a little wider than neck of head; surface of pronotum with punctation sparse and shallow, including longitudinal, oval punctures, interspaces with reticulate microsculpture, pubescence moderately dense and short, directed from sides posteriorly and towards midline; anterior margin with setae mainly directed anteriorly and towards middle on each side.

Scutellar shield wide, about twice as wide as long, width slightly less than eye length.

Elytra ( Fig. 1A ) elongate, oval, EL 1.66–2.05 mm, EW 0.73–1.00 mm (greatest width posterior to middle), EW/BL 0.26–0.30, EW/EL 0.44–0.49 (n=4), with widely rounded apices. Strial punctures small and very shallow, bearing short thick setae on anterior margins. Lateral margins with many minute denticles at bases of setae, without obvious humeral tooth.

Hind wing absent.

Legs ( Fig. 2B ) long, with reticulate to rugose microsculpture, covered with many short setae, thinner than those of pronotum; femora thick, profemora moderately expanded; tibiae gradually widening distally, apically with some short conical spine-like setae; tarsi ( Fig. 2C ) long, tarsomeres I–III large and lobed; claws simple.

Ventral surface ( Fig. 1B ). Metaventrite long, about 3/4× as long as abdominal ventrite I, with punctation sparser than on pronotum; mesoventrite with larger and deeper punctation than other ventrites; setae thinner than those of pronotum, each located by a puncture and directed anteriorly on prosternum, and posteriorly on meso- and metaventrites; ventrites mostly covered with coarse transverse microsculpture; intercoxal process of procoxae widening toward base; mesocoxal process narrowed posteriorly, somewhat widened near apex. Abdomen more than 1.5× as long as wide; intercoxal process narrowed towards base and rounded; femoral line absent; setae short and thin.

Male genitalia ( Figs 2 B–H). Tergite VIII transversely oblong, about twice as long as wide, with many short setae along posterior margin; sternite VIII with paired small oblong plates connected by a membrane, ventrally with several very short setae, with two setae of medium length on each posterior portion; sternite IX Y-shaped, widening around middle; branches with moderately sclerotized plates, densely pubescent with short setae on each inner area ( Fig. 2B ). Median lobe ( Figs 2C, D ) with rounded apex, longer than wide, with sparse and weak punctation on apical 1/4; median strut Y-shaped with short branches, long and somewhat broad, less than 3× as long as median lobe; ostium opening ventrally around apex ( Fig. 2C ). Parameres ( Fig. 2E ) elongate, enlarged at basal 1/3, gradually narrowed toward apex, connected to each other at inner margin of basal 1/3, except on area around basal inner margin covered with many short setae, with some median length to long setae around apices. Phallobase ( Fig. 2E ) moderately long; tegminal strut short Y-shaped, branches widely divergent with a membrane between them; basal piece transversely oblong, with long branches extending from anterior angles and connected to tegminal strut, a membrane present between branches, posterior margin concave at junction of parameres. Internal sac ( Fig. 2D ) very long, apex with a long and thin strut (ejaculatory duct) and a U-shaped small plate, with long and more or less angulated armature in apical half, U-shaped thin strut around basal half.

Differential diagnosis. Airaphilus abei sp. nov. is similar to A. filiformis (Rosenhauer, 1856) , another apterous species, but it can be distinguished by having the following characters: 1) Antennae about half as long as body (similarly long antennae present also in a few other species); in A. filiformis obviously less than half as long. 2) Anterior margin of pronotum narrow, about as wide as (not wider than) head across eyes; in A. filiformis wider than head across eyes. 3) Elytra without a humeral tooth, somewhat rounded to base and more rounded to apices; in A. filiformis elytra each with a poorly developed humeral tooth, distinctly narrowed to base and more narrowed to apices. 4) Metaventrite, about 3/4 as long as abdominal ventrite I; in A. filiformis metaventrite shorter, about 1/2 the length of this ventrite. The general appearance of the new species (head, thorax, and elytra) particularly the shape of the pronotum, also the absence of a femoral line on the abdominal ventrite I (in contrast to those species where it is present) plus characters given above, are also useful for distinguishing A. abei sp. nov. from other superficially similar ones.

As far as the authors are aware, male genitalia of Airaphilus species have been illustrated for only three species; those of A. serricollis Reitter, 1878 were illustrated and described by SENGUPTA & PAL (1996), and those of A. doramas Wurst & Lange, 1996 were similarly treated by WURST & LANGE (1996). Genitalia of A. seabrai Luna de Carvalho, 1951 were illustrated without description by LUNA DE CARVALHO (1951). Comparison of the genitalia of A. abei sp. nov. with these published illustrations showed that the new species differs from them in the form of one or more parts, i.e., parameres, including shape and/or setae on them, median lobe and basal piece. A few additional species, examined by one of the authors (D. Halstead), also revealed some differences in these parts suggesting that male genitalia, particularly the parameres, may provide a guide to species limits and be helpful in identification.

Biological notes. All specimens were collected from the marsh vegetation with ground beetles and/or diving beetles.

Etymology. This new species is dedicated to Dr. Azuma Abe who collected all of the type specimens.

Distribution. Japan (Aomori Prefecture).

Figures

Fig. 1. Airaphilus abei sp. nov., habitus of holotype (male). A – dorsal view; B – ventral view. Scale: 1.0 mm.

Fig. 2. Airaphilus abei sp. nov., holotype (male), antenna and genitalia. A – right antenna; B – abdominal sternites VIII and IX, ventral view; C – apex of median lobe, dorsal view; D – median lobe, ventral view, including internal sac; E – phallobase, ventral view, including parameres. Scale: 0.4 mm for A; 0.2 mm for B, D, E; 0.1 mm for C.

Fig. 3. Airaphilus abei sp. nov. A – SEM image of metathorax from which left elytron was removed; B – in detail. Scale: 0.1 mm.