Diaulota aokii Sawada, 1971

[Japanese name: Aoki-tsutsumune-umi-hanekakushi]

(Figs. 1B; 2D & E; 5A; 6A, B, D & G; 7; 23A & B)

Diaulota aokii Sawada, 1971: 104 (original description; type locality: Izu-ôshima).

Type material. Holotype. Female, “ Diaulota aokii K.S. / 伊ük島元村 / 8 III ’51 T. AOKI leg / (Holotype)” (whole body dissected (spermatheca lost), all dissected parts on a slide glass with Myrmecopora sp.) (OMNH).

Material examined. Japan: Honshû: Tôkyô-to: 2 males, 1 female, 29 unsexed, Izu-ôshima (Ôshima), Okada, Noda-hama, 15. V. 2022, H. Ono & Y. Tasaku (KUM, cHO & cYT) ; Chiba-ken: 2 unsexed, Futtsu-shi, Kanaya, Kanaya-kô, 18. VIII. 2009, H. Ono (cHO); 1 male, 2 unsexed, ditto, 31. III. 2021, H. Ono (cYT) ; Kanagawa-ken: 3 unsexed, Miura-shi, Hasse-machi, Wada, 30. X. 2022, Y. Kanzawa (cYT) .

Diagnosis. This species can be distinguished from other Diaulota species by the combination of the following characteristics: mentum as long as wide (Fig. 7B); apical lobe of median lobe unilobed in lateral view (Fig. 6D); body slender, entirely reddish black and covered with thin and short setae (Fig. 5A) (see also the diagnosis of D. decipiens sp. n.).

Supplementary description. Male: sternite VIII cuspidate on apical margin, covered with setae; tergite VIII wider than long, apical margin truncate; median lobe of aedeagus gently bent (Fig. 6A); apical lobe unilobed and rounded at apex in lateral view (Fig. 6D); almost parallel, and apical lobe slightly pointed at apex in ventral view (Fig. 6B); paramere slender (Fig. 2D), apical lobe narrow rectangle (Fig. 2E).

Remarks. This species was originally described by Sawada (1971) based on a single female specimen collected from Izu-ôshima, south of Tôkyô (central Honshû), Japan. In the original description, its tarsal formula was described as 4-4-4. Subsequently, Ahn (1996) redescribed the species based on the specimens from Alaska, Hokkaidô (Japan) and Korea, including male characteristics. Ahn mentioned that the tarsal formula of this species could be 4-4-4 or 4-4-5, and the apical lobe of the median lobe is apically divided.

Recently, Song et al. (2018) described a species, D. hokkaidona previously considered as “ D. aokii ” from Hokkaidô, Alaska, and Kamchatka, so the true D. aokii was considered to be distributed in Honshû and Korea. However, the holotype or individuals collected in the type locality were not examined in their study.

In this study, we conducted a survey on Izu-ôshima, collected true D. aokii, and examined its a detailed morphology. The results revealed that true D. aokii from Izu-ôshima consistently exhibits a tarsal formula of 4-4-4, and the apical lobe of the median lobe is unilobed in lateral view. Similarly, individuals from the Kantô district in central Honshû were also found to have the same characteristics. Hence, it is most likely that the true distribution of D. aokii is confined to the vicinity of Izu-ôshima and the Kanto district. The representation of the Korean " D. aokii " in Ahn (1996) and Song et al., (2018) is likely a result of misidentification. Given that recent phylogenetic investigations (Ahn & Ashe, 1996b; Ahn et al., 2010; Song et al., 2018; Yoo & Ahn, 2021) were founded on this erroneous identification, it is imperative to conduct further analyses of Diaulota based on the accurate identification.

Diaulota . aokii, the Korean “ D. aokii,” D. decipiens sp. n., and D. hokkaidona are undoubtedly related species based on similarities in external morphology and also their habitats (we consider them as the Diaulota aokii species-complex). Their distribution areas need further investigation.

Habitat. This species is found in rock crevices on the rocky shore (Fig. 23B).

Distribution. Japan: central Honshû (Kantô district and Izu-ôshima) (Fig. 23A).