Rotundicephala pacifica (Sawada, 1971), comb. n.

[Japanese name: Kuroshio-umi-hanekakushi]

(Figs. 14A & B; 15A, B & G; 25A & C)

Diaulota pacifica Sawada, 1971: 101 (original description; type locality: Kirime-zaki, Wakayama-ken, Honshû).

Type material. Holotype. Male, “ Genoplectes ? / pacificus / IJh崎, 15. IV. ’70 / (Holotype) K.S.” (whole body dissected) (OMNH).

Other material examined. Japan: Honshû: Okayama-ken: 19 unsexed, Kurashiki-shi, Ôbatake, Kusumihana, 8. VI . 2003, Y. Fujitani (KUM, OMNH) . Yamaguchi-ken: 1 male, 1 female, 3 unsexed, Hôfu-shi, Mukô-shima, Tano-ura, 5. VI . 2003, Y. Fujitani (KUM) ; 1 female, Shimonoseki-shi, Chôfu-sangen’ya-kaigan, 25. V . 2012, M. Matsuda (cYT); 1 female, ditto, 8. V . 2013, M. Matsuda (cYT); 1 male, ditto, 20. I. 2015, M. Matsuda (cYT); 1 male, ditto, 23. II . 2015, M. Matsuda (cYT); 1 female, ditto, 24. II . 2015, M. Matsuda (cYT); 2 males, ditto, 11. III . 2015, M. Matsuda (cYT). Shikoku: Kagawa-ken: 2 unsexed, Marugame-shi, Te-shima Is. (off Shikoku), 23. IV . 2017, H. Fujimoto (cYT). Kyûshû: Fukuoka-ken: 1 female, Kitakyûshû-shi, Moji-ku, Shiranoe, 7. II . 2016, M. Matsuda (cYT); 2 females, Kitakyûshû-shi, Moji-ku, Kitaku, 6. VI . 2016, M. Matsuda (cYT). Nagasaki-ken: 1 male, 1 female, 1 unsexed, Kamiamakusa-shi, Mae-shima, 9. VI . 2021, H. Nakamura (KUM) . Tsushima: 1 male, 1 female, 7 unsexed, Izuhara-machi, Azamo, 18. VI . 2022, Y. Tasaku (KUM, OMNH, cYT) , 4 males, 9 unsexed, ditto, 15. VI . 2022, H. Ono (cHO). Ryûkyû: Kagoshima-ken: Tanega-shima: 2 females, Nishino’omote-shi, Asakawa, 27. III . 2010, M. Asano (cYT).

Diagnosis. This species is similar to other species of this genus. Compared with R. koheii sp. n., this species differs in the following characteristics: head and pronotum flattened; antennal segments IV–VIII transverse (Fig. 15G); male heads slightly larger than that of female. Compared with R. koreana comb. n., this species can be distinguished by the short antennae not reaching to elytral apex.

Redescription. Body small, robust, weakly shining (Figs. 14A & B). Ground color reddish brown, head usually darker, abdominal segments V–VII sometimes blackish, legs and month parts slightly paler (Figs. 14A & B).

Head flattened, rounded, as long as wide (MHL/MHW=1.02); eyes small; antennae almost as long as head and pronotum combined, segments IV–X transverse, segment XI oval and longer than X (Fig. 15G). Labrum transverse, with about 20 setae; epipharynx with 6 lateral setae. Mandibles long, pointed at apex. Mentum almost trapeziform, anterior margin deeply emarginated, with about 10 setae. Pronotum flattened, transverse. Tarsal formula 3-3-4. Abdomen oblong oval.

Male: head slightly larger than in female (Fig. 14A); apical lobe of median lobe bent almost at a right angle (Fig. 15A).

Female: spermatheca short, coiled one time at base (Fig. 15B).

Measurements. Male (N = 7): BL, 1.91–2.33 mm; FBL, 0.88–1.03 mm; HW, 0.39–0.48 mm; PL, 0.34–0.40 mm; PW, 0.39–0.44 mm; EW, 0.37–0.40 mm; HW/PW, 1.01–1.07. Female (N = 7): BL, 1.99–2.33 mm; FBL, 0.86– 1.05. mm; HW, 0.37–0.44 mm; PL, 0.33–0.43 mm; PW, 0.38–0.43 mm; EW, 0.35–0.41 mm; HW/PW, 0.94–1.02.

Remarks. This species was originally described by Sawada (1971) and later redescribed by Ahn (1996). In Sawada's description, its tarsal formula was noted as 3-3-4, while Ahn's description indicated a tarsal formula of 3-3-4 or 4-4-4. Ahn (1996) examined only Korean specimens which have a tarsal formula of 4-4-4. Through our comprehensive study using numerous specimens collected from Honshû including the holotype, we have established that the true R. pacifica comb. n. is defined by the following characteristics: a tarsal formula of 3-3-4 (without exception), reddish-brown body color, and a nearly circular head. Consequently, the species described in Ahn (1996) as “ D. pacifica ” is not this species. The Korean “ D. pacifica ” is considered to be a species of Diaulota conferring an essential distinguishing characteristic of Rotundicephala gen. n., namely the 3-3-4 tarsal formula. Several taxonomic and phylogenetic studies were based on this misidentification (e.g., Kim et al., 2000; Ahn et al., 2010; Song et al., 2018; Yoo & Ahn, 2021), hence larval morphological study and the systematic position of this species requires reevaluation.

Habitat. This species has been collected from rock crevices of rocky beaches with minimal seaweed presence (Fig. 25C).

Distribution. Japan: Honshû, Shikoku, Kyûshû, Tsushima, Ryûkyû (Tanega-shima) (Fig. 25A).