Rotundicephala Tasaku, Ono & Maruyama, gen. n.

[Japanese name: Kuroshio-umi-hanekakushi-zoku]

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

Diagnosis. This new genus is similar to Diaulota but can be distinguished by a combination of the following characteristics: tarsal formula 3-3-4, head almost circular (Fig. 1C), body color usually reddish brown (Fig. 14). Abdomen is more elongate than that of Diaulota . See also the diagnosis of Diaulota .

Description. Body small; reddish brown in ground color, abdominal segments V–VII almost black in most cases, mouthparts and legs slightly paler. Head slightly convex or flattened, almost circular, as long as wide (Fig. 1C); eyes small; infraorbital carina present; antennae 11-segmented, segments I–III strongly elongate, segment I longer than II, segment III shorter than II, segments IV–XI moniliform (Figs. 15G–I). Labrum semicircular (Fig. 16A). Mandibles almost symmetric, with one large tooth present around middle, and right teeth larger than left one (Fig. 16E). Prementum without medial seta; ligula unilobed, very short, about 1/3 length of segment I of labial palpus; labial palpus two-segmented, segment I incompletely divided in basal 1/3, segment I very long, and segment II short and thin (Fig. 16C). Maxilla slender; lacinia with about 8 spines; maxillary palpus 4-segmented, segment I very short, segment II three times as long as I, segment III longer than II, and segment IV as long as I (Fig. 16D). Mentum almost trapeziform, anterior margin deeply emarginated (Fig. 16B). Pronotum almost oval. Elytra short. Hind wings reduced. Tarsal formula 3-3-4. Abdomen oblong oval.

Male: tergite VIII with truncate apical margin; sternite VIII cuspidate at apical margin; apical lobe of median lobe unilobed and strongly curved, athetine bridge absent (Figs. 15A, C & E); apical lobe of paramere narrow rectangle (Fig. 2G).

Female: tergite VIII with truncate apical margin; sternite VIII rounded at apical margin.

Remarks. In a previous study, Sawada (1971) classified R. pacifica comb. n. within Diaulota, noting that there were no fundamental differences except for the tarsal formula from other Diaulota species. However, Yoo & Ahn (2021) suggested that R. koreana comb. n. may not actually belong to Diaulota . This study confirms that three species belonging to Rotundicephala gen. n. share two important morphological characteristics: a rounded head and a tarsal formula of 3-3-4. These two characteristics are not found in Diaulota . While the reduction of tarsi is often observed in Liparocephalini, the exclusive 3-3-4 tarsal formula is a distinctive character state of Rotundicephala gen. n. to distinguish it from Diaulota .

Etymology. The generic name means round head. Gender feminine.

Distribution. Japan: Honshû, Shikoku, Kyûshû; South Korea.

Key to the species of Rotundicephala gen. n.

1. Antennae long, reaching to elytra, collected from gravel beach.................................. R. koreana comb. n.

- Antennae short, not reaching to elytra, collected from rocky shore............................................... 2

2. Head and pronotum slightly convex, antennal segments IV–IX as long as wide......................... R. koheii sp. n.

- Head and pronotum flattened, antennal segments IV–VIII transverse.............................. R. pacifica comb. n.