Cephennomicrus aji, Jałoszyński, 2021

Jałoszyński, Paweł, 2021, Two new species of Cephennomicrus in the Ryūkyū Archipelago (Coleoptera Staphylinidae, Scydmaeninae), Zootaxa 4938 (5), pp. 581-587 : 582-584

Cephennomicrus aji sp. n.

( Figs 1–5 , 11 )

Type material. Holotype: JAPAN (Okinawa Island): ♁, two labels: “JAPAN, OKINAWA Island / Motobu Penins., near Nakijin Castle, ~ 50 m, / humid forest, 12.02.2019 / leg. P. JAŁOSZYŃSKI” [white, printed], “ CEPHENNOMICRUS / aji m. / P. Jałoszyński, 2021 / HOLOTYPUS” [red, printed] ( NSMT).

Diagnosis. Body extremely small, below 0.7 mm in length, covered with very short, barely discernible recumbent setae, lacking macrosetae; head in male unmodified; punctures on head, pronotum and elytra fine, superficial and inconspicuous, cuticle glossy; antennal club dimerous and sharply demarcated; pronotum with sides strongly convergent posterad and with two pairs of distinct antebasal pits not connected by transverse groove; aedeagus in ventral view elongate, with sides indistinctly narrowing toward truncate apex; ventral diaphragm small and situated in sub-basal third; median lobe of aedeagus in lateral view broadest at the level of diaphragm and weakly narrowing distad; endophallus with median tubular structures, two of them in lateral view strongly recurved, S-shaped; parameres so thin that barely discernible, each with two apical setae.

Description. Body of male ( Fig. 1 ) moderately stout, strongly convex, uniformly and moderately dark brown; setae slightly lighter than cuticle and barely discernible; BL 0.66 mm.

Head broadest at large, moderately strongly convex and finely faceted eyes, HL 0.06 mm, HW 0.15 mm; vertex and frons between eyes evenly, strongly convex; frontal glands not discernible. Punctures and setae on frons and vertex indiscernible under magnification 100 ×. Antennae slender, with sharply delimited, large dimerous club, AnL 0.28 mm; antennomeres 1–2 each elongate, 3–9 each about as long as broad, 10 indistinctly transverse and more than twice as broad as 9, 11 much longer than 10 but similar in width, about 1.5 × as long as broad.

Pronotum subtrapezoidal, broadest near anterior third; PL 0.23 mm, PW 0.28 mm; anterior margin in strictly dorsal view nearly straight; lateral margins strongly rounded in anterior half, nearly straight, indistinctly microserrate and strongly convergent posterad in posterior half; posterior corners obtuse-angled; posterior margin barely noticeably bisinuate. Pronotal base with two pairs of small but deep circular pits, inner pair not connected by groove, distance between inner pits slightly wider than between inner and outer pit. Punctures on pronotum extremely fine, inconspicuous; setae extremely short but dense, recumbent.

Elytra together oval, broadest distinctly in front of middle; EL 0.38 mm, EW 0.31 mm, EI 1.20; humeral calli and short basal impressions distinct; subhumeral lines lacking; sides of elytra strongly rounded; elytral apices separately rounded. Punctures and setae similar to those on pronotum.

Hind wings long and functional.

Legs moderately long and slender, unmodified.

Aedeagus ( Figs 2–5 ) elongate and relatively large in relation to body; AeL 0.20 mm; median lobe in ventral view with sides indistinctly convergent distad; apex truncate, subtrapezoidal; ventral diaphragm small, circular and situated in sub-basal third, with dark lentiform internal sclerotization (visible in Fig. 3 ) to which transverse muscle fibers are attached; in lateral view aedeagus weakly narrowing distad, broadest at the level of diaphragm; endophallus with three tubular structures, well discernible in lateral view; one of these structures is weakly curved dorsad, and two are strongly recurved, S-shaped, and their tips are directed ventrad or distoventrad. Parameres extremely slender, each with slightly expanded apex bearing two setae.

Female. Unknown.

Distribution. Japan, Okinawa-jima ( Fig. 11 ).

Etymology. Aji (a noun in apposition) was a title and rank of Okinawan nobility; the holotype of Cephennomicrus aji was collected near ruins of the Nakijin Castle (Okinawan: Nachijin Gushiku), headquarters of Nakijin Aji.

Remarks. This species has the smallest adults of all Japanese Cephennomicrus . With the body length merely 0.66 mm, it is much smaller than the second smallest C. ushimanus described below. All previously known Japanese species have the body length ranging from 0.89 to 1.17 mm. Externally, C. aji is inconspicuous; it does not have any macrosetae that form a specific pattern in other species (except for those that belong to the nomurai group, which is remarkable in having a longitudinal groove on the pronotum in both sexes and modifications on the frons in males). The aedeagus of C. aji is unique among all Cephennomicrus species known so far; among Japanese congeners it can be easily distinguished by the general shape of the median lobe in ventral view. Only species that belong to the taiwanensis group (see Jałoszyński (2009a)) have strongly elongate aedeagi with variously developed (but frequently looped) tubular endophallic structures. However, none of them has the median lobe nearly parallel-sided as that in C. aji . The aedeagi of Japanese members of this group, i.e., C nagoanus Jałoszyński and C. iriomotensis Jałoszyński , have the median lobes (illustrated in Fig. 11 ) strongly tapering toward a subtriangular apex. As more Cephennomicrus species can be expected to be discovered on Okinawa-jima and other southern islands, and external characters in this genus are relatively uniform, examination of the aedeagus is required to identify new specimens.

The holotype was collected by sifting moist rotten wood of a deciduous tree on a densely forested hillside facing east.

Figures

FIGURE 11. Distribution of nominal Cephennomicrus species within Japan, with aedeagus of each species in ventral view (that of C. tanakai based on Hoshina (2011)).

FIGURES 1–10. Cephennomicrus aji sp. n. (1–5) and C. ushimanus sp. n. (6–10). Dorsal habitus of holotype male (1, 6), and aedeagus in ventral (2, 4, 7, 9) and lateral (3, 5, 8, 10) views.