Dendronotus zakuro Martynov & Fujiwara & Tsuchida & Nakano & Sanamyan & Sanamyan & Fletcher & Korshunova 2020, sp. nov.

Dendronotus zakuro sp. nov.

(Figures 1, 3, 5B)

http://zoobank.org/ 3B54EB14-A55E-42C5-B962-82D6A40B9BF5

Type material. Holotype, ZMMU Op-700, 30 mm long live, 15 mm preserved, dissected, Russia, Kamchatka, Starichkov Island, 17.07.2015, depth— 12 m, on stones, collector N.P. Sanamyan. Two paratypes, KSNHM-OP0485, Japan, Hokkaido, Usujiri, 10 and 12 mm long (preserved), 13.03.2016, depth 10–20 m, stones, collector Sho Kashio One paratype, ZMMU Op-664, 25 mm long live, Japan, Honshu, Echizen Coast, Fukui Prefecture, 19.04.2018, depth 7.1 m, collector Chihiro Dairi.

Type locality. Russia (Kamchatka) and Japan (Hokkaido; Honshu: Sea of Japan).

Etymology. From zakuro (ẈŽo, HAE×ďAE), meaning in Japanese “pomegranate”, after a striking red to red-brownish colouration of the new species.

Diagnosis. Body elongate, 6–7 pairs dorsolateral appendages, colour bright reddish to reddish-brownish with opaque white spots, central tooth completely smooth (in adults), lacking denticles and furrows, vas deferens moderate in length, penis massive, long, twisted.

Description. Body elongate, up to 30 mm in length (Fig. 3 A–E), 5–7 branched appendages of oral veil, ca. 5 appendages of rhinophoral stalks, 10–11 rhinophoral lamellae, branched rhinophoral lateral papilla present, 6–7 pairs dorsolateral appendages, 25–30 lip papillae. Dorsolateral appendages with elongate primary stalk, moderately relatively highly branched secondary branches, and attenuated tertiary branches (Fig. 3 A–E). Reproductive and anal openings placed laterally on right side. General colour bright red to reddish-brownish with thin white broken lines between dorsolateral appendages, also scattered opaque white dots and speckles on dorsal and lateral sides, and on various appendages (Fig. 3 A, D, E).

The jaws are ovoid with strong dorsal processes, denticles present (Fig. 3 F–G). Masticatory processes bear up to 120 denticles. Radula formula is 36 × 3–11.1.11–3 (holotype), 34 × 3–12.1.12–3 (paratype, 12 mm). Central tooth completely devoid of denticles and furrows in most parts of the radula (except for the anterior-most juvenile radula in some specimens) only faint traces of the furrows on the surface appear on some teeth in the holotype (Fig. 3H, J); the studied paratype possesses almost completely smooth central teeth throughout the whole radula. Lateral teeth are long, distinctly curved, bearing up to 7 long denticles (Fig. 3I, K).

Reproductive system triaulic (Fig. 5B), ampulla thin, twice folded (Fig. 5B, am), prostate consisting of ca. 25 alveolar glands (Fig. 5B, pr), vas deferens relatively long (Fig. 5B, vd) expanding to voluminous penial sheath (Fig. 5B, psh), penis long and twisted (Fig. 5B, p), vagina long and straight (Fig. 5B, vg), bursa copulatrix is large, rounded, and elongated (Fig. 5B, bc) with small seminal receptaculum placed distally (Fig. 5B, rs).

Biology. Inhabits stony and rocky substrates, 7– 20 m.

Distribution. Presently known from three remote locations in the North Western Pacific, from Hokkaido Island and Echizen coast (Honshu) in Japan and Starichkov Island, Kamchatka in Russia. Further intermediate findings on the Kurile Islands between these two remote points are therefore expected.

Remarks. D. zakuro sp. nov. by combination of colouration, radular patterns and molecular phylogenetic data well differs from all previously described species of the genus Dendronotus. The almost smooth central teeth in adult radular morphology combined with the non-uniform, partly variegated external colouration of D. zakuro sp. nov. is only similar to D. kamchaticus. However, D. kamchaticus is phylogenetically distantly related to D. zakuro sp. nov. (Fig. 1). Furthermore, morphologically D. zakuro sp. nov. differs from D. kamchaticus by bright red to redbrownish colouration (the known range of colouration for D. kamchaticus is brownish to transparent greyish, see Korshunova et al., 2016a), larger number of rows of lateral teeth and patterns of their denticulations. D. subramosus with commonly brownish general colouration considerably differs from D. zakuro sp. nov. by the absence of lateral rhinophoral papillae and strongly denticulated central radular teeth. According to molecular phylogenetic analysis, evolutionary ties for D. zakuro sp. nov. are not fully clarified. Clade D. zakuro sp. nov. has the closest position to the clades D. arcticus, D. dalli, D. kamchaticus, D. niveus, D. lacteus, D. europaeus and D. rufus (Fig. 1), but none of these species (except D. kamchaticus) demonstrate any external or internal similarity to D. zakuro sp. nov. Maximum intraspecific and minimum interspecific genetic distances for the COI marker in the species of the genus Dendronotus including D. zakuro sp. nov. are presented in the Table 2.