Ochthebius (Ochthebius) sasakii, Yoshitomi, Hiroyuki, Karube, Haruki & Hayashi, Masakazu, 2019

Yoshitomi, Hiroyuki, Karube, Haruki & Hayashi, Masakazu, 2019, A new species of the genus Ochthebius (Coleoptera, Hydraenidae) from the Ogasawara Islands, Japan, with a description of the larva, ZooKeys 855, pp. 95-107 : 97-103

Ochthebius (Ochthebius) sasakii sp. nov. Figs 1, 2, 3, 4, 5 Japanese name: Ogasawara-sesuji-darumagamushi

Type series.

Holotype (EUMJ): male, "Higashi-kaigan, Chichi-jima, Ogasawara Isls., Japan, 22.II.2018, H. Karube leg.". Paratypes (EUMJ, NMW, KPMNH): 5 exs, same data as for the holotype; 10 exs, same locality and collector, but “24.II.2019”; 1 ex., same locality and collector, but “25.II.2019”; 10 exs, "Inui-sawa, Ani-jima, Ogasawara Isls., Japan, 22. II. 2018, H. Karube leg."; 6 exs, "Kohama, Otouto-jima, Ogasawara Isls., Japan, 22.II.2018, H. Karube leg.".

Diagnosis.

Ochthebius (Ochthebius) sasakii belongs to the punctatus species group (sensu Villastrigo et al. 2019) and is similar to two Japanese species, O. inermis and O. danjo . The adult of O. sasakii differs from the two Japanese species in having a smaller body size (see Table 1), anterior margin of labrum not shallowly concave, median groove of pronotum shallow, and short elytral setae. The larva of this species differs in the following characteristics: mandibles strongly curved inwardly in the apical part (gently curved in O. inermis and O. danjo ); labrum arcuate in anterior margin (projecting apically in O. inermis ); and presence of subprimary setae on pronotum and mesonotum (see Table 2).

Description.

Adults. Body oblong, slightly convex dorsally, weakly shiny in dorsal surface. Coloration of body black, with weak bluish lustre; ventral surface of body blackish brown; antennae, maxillary palpi and legs yellowish brown, but fuscous in antennomeres IV–IX, terminal palpomere of maxillary palpi and femur.

Head (Fig. 1B) finely punctate, distinctly microreticulate, with deep ocular grooves, closely covered with short setae; fronto-clypeal suture straight. Labrum (Figs 1B, 2C) transverse, finely punctate, almost straight in front margin from dorsal view (Fig. 1B), but shallowly concave from antero-dorsal view (Fig. 2C). Maxillary palpi (Fig. 2B) long, provided with oblong terminal palpomere; approximate ratio of each palpomere (n = 1) as 10: 14: 9. Antennae (Fig. 2A) relatively short; approximate ratio of each antennomere (n = 1) as 22.5: 9.0: 4.5: 1.0: 1.5: 3.0: 2.5: 2.0: 7.0. Pronotum (Fig. 1C) transversely rectangular, widest at anterior 1/3, finely punctate, distinctly microreticulate, bearing short setae same as in head; anterior margin almost straight, without postocular tooth; posterior margin slightly bisinuous; lateral margins arcuate in anterior parts, straightly tapered in posterior parts; median groove shallow; anterior and posterior discal foveae shallow and indistinct; lateral portions ( “ear” in Jäch 1998) slightly depressed dorsally; hyaline membranous cuticula present on anterior and posterior margins; PW/PL 1.21-1.50 (1.36). Elytra oval, gently arcuate in lateral margins, broadest at the middle, irregularly and finely punctate, bearing fine short suberect setae; lateral gutter narrowly explanate; epipleura pubescent, almost reaching elytral apices; elytral apices subacuminate; EL/EW 1.31-1.53 (1.41); EL/PL 2.29-2.98 (2.66); EW/PW 1.24-1.50 (1.39); TL/EW 2.17-2.75 (2.42). Metaventrite pubescent. Legs rather long and slender. Ventrites I–V pubescent; ventrite VI glabrous.

Male. Sternite X (Fig. 2F) subtriangular, with long spiculum. Aedeagus (Fig. 2D, E) ca 0.4 mm, gently curved ventrally; main piece pointed at apex, with three minute setae in subapical area; parameres long, close to main piece, expanded in apical parts.

Female. Sexual dimorphism indistinct in elytral gutter and elytral apices. Capsule of spermathecal duct (Fig. 2G) relatively short.

Measurements (n = 13). TL 1.83-2.16 (2.00) mm; HL 0.30-0.42 (0.39) mm; PW 0.55-0.63 (0.60) mm; PL 0.40-0.48 (0.44) mm; EL 1.03-1.28 (1.17) mm; EW 0.72-0.90 (0.83) mm.

Description of third instar larva

(based on a damaged specimen collected with adults from Chichi-jima). Body about 2.0 mm in fully expanded specimen. Coloration of body blackish brown, weakly shining; legs infuscate. Head (Fig. 3A) with five stemmata on each side. Labrum (Fig. 3B) arcuate in anterior margin. Antennae (Fig. 3C) short; IIS1 long, slightly longer than antennomere III; antennomere III about 0.5 times as long as antennomere II. Mandibles (Fig. 3D) strongly curved inwardly in apical parts. Maxillae (Fig. 3E) with palpomere III long and slender. Labium (Fig. 3F) with short mentum. Urogomphi (Fig. 3G) relatively short; URI stout, 4.5 times as long as URII. Chaetotaxy on head capsule, labrum, antennae, maxillae, labium, and urogomphi same as in O. danjo ( Delgado and Matsui 2000). Pronotum (Fig. 4A) about 1.8 times as wide as long; four anterior (A1-A4), three lateral (L1-L3), four posterior (P1-P4), row of Da1, Db1, and Dc1, four subprimary setae ( Da’, Db’, Dc’, Dc’’), and three campaniform sensilla (C1, C4, C5) present on each side. Mesonotum (Fig. 4B) about 2.5 times as wide as long, four anterior (A1-A4), three lateral (L1-L3), four posterior (P1-P4), row of Da1, Db1 and Dc1, subprimary setae ( Da’), three campaniform sensilla (C3-C5) present on each side; A4 somewhat longer. Abdominal tergum I (Fig. 4C) about 4.4 times as wide as long, three anterior (A1, A3-A4), three lateral (L1-L3), four posterior (P1-P4), DP1 and DP2, two campaniform sensilla (C3, C5) present on each side.

Biological notes.

All the specimens (both adults and larvae) were collected from the surface of littoral rocks covered with a film of sheeting fresh water (depth ca 1-2 mm; Fig. 5). All habitats are situated on the seashore (the nearest point from the edge of the water was ca 3 m); we could not find any habitats in inland areas.

The fauna of the Ogasawara Islands was seriously affected by a long drought in 2016-2017. In addition, a serious drought occurred from autumn to winter 2018/2019. In February 2018, HK found many individuals of O. sasakii sp. n. at the Ani-jima site (Fig. 5E) and collected some specimens as the type series. However, in February 2019, HK could not find this species at this site because sheeting fresh water had completely dried up. At the Chichi-jima site, HK found many individuals of this species in both 2018 and 2019, but the area of sheeting fresh water was markedly reduced.

Distribution.

Ogasawara Isls. (Chichi-jima, Ani-jima, Otouto-jima).

Description of third instar larva of Ochthebius inermis

Specimens examined.

20 exs (mature larvae, EUMJ), Shakunouchi-koen, Unnan-shi, Shimane Pref., 24.VI.2006, M. Hayashi leg.

Description.

Body about 3.0 mm in fully expanded specimens. Coloration of body black, strongly shining; legs cream (see Hayashi 2008a: fig. 2F). Head (Fig. 6A) with five stemmata on each side. Labrum (Fig. 6B) projecting apically in anterior mar gin. Antennae (Fig. 6C) long; IIS1 long, as long as antennomere III; antennomere III long, about 0.6 times as long as antennomere II. Mandibles (Fig. 6D) gently curved inwardly in apical parts. Maxillae (Fig. 6E) with palpomere III long and slender. Labium (Fig. 6F) with long mentum. Urogomphi (Fig. 6G) relatively long; URI slender, about 6.5 times as long as URII. Chaetotaxy on head capsule, labrum, antennae, maxillae, labium, and urogomphi same as in O. sasakii sp. n. and O. danjo ( Delgado and Matsui 2000; present study). Pronotum (Fig. 7A) about 2.0 times as wide as long; four anterior (A1-A4), three lateral (L1-L3), four posterior (P1-P4), row of Da1, Db1 and Dc1, five campaniform sensilla (C1-C5) present on each side. Mesonotum (Fig. 7B) about 2.5 times as wide as long; four anterior (A1-A4), three lateral (L1-L3), four posterior (P1-P4), row of Da1, Db1 and Dc1, three campaniform sensilla (C3-C5) present on each side. Tergum I (Fig. 7C) about 3.3 times as wide as long; three anterior (A1, A3-A4), three lateral (L1-L3), three posterior (P1, P3-P4), DP1, and DP2 setae, two campaniform sensilla (C3, C5) present on each side.