Dendronotus kamchaticus Ekimova, Korshunova, Schepetov, Neretina, Sanamyan et Martynov, 2015

Dendronotus kamchaticus Ekimova, Korshunova, Schepetov, Neretina, Sanamyan et Martynov, 2015 View in CoL

Fig. 6–8 View Fig View Fig View Fig .

Type material: Holotype ZMMU Op-245, northwest Pacific, Kamchatka, Avacha Bay , 7 m depth, coll. D.B. Semenov, 15 June 2010.

Material examined: W194, 2 specimens, Sea of Japan, Rudnaya Bay, 10–16 m depth, coll. T. Antokhina, A. Chichvarkhin, 8 May 2013 .

Description. External morphology ( Figs. 6 View Fig , 8A View Fig ): Body elongate, laterally compressed. Foot narrow, tail short. Oral veil with 4–6 lip papillae and branched appendages. Primary stalks of veil appendages tall and slender, giving rise to numerous secondary branches with short tertiary branches. Rhinophoral sheath divide into 5– 6 crown papillae that about same length. Lateral papillae (about one-third or one-half of sheath length) branches off sheath base and expanded with secondary branches. Rhinophores bear 14– 20 lamellae. 5 pairs of dorsolateral appendages. Primary stalks of cerata long, slender and conical ( Fig. 8A View Fig ). Secondary branches of dorsal appendages well-expressed, narrow; tertiary branches of dorsal appendages short, rounded at tip. Digestive gland diverticula penetrate cerata and rhinophoral branched processes. These diverticula in first part of cerata and rhinophores originate from anterior lobe of digestive gland; others arise from posterior lobe. Anal opening on right side of body about midway between first and second pair of dorsal appendages. Reproductive openings lateral near the first pair of cerata on right side.

Colour ( Fig. 6 View Fig ): Background colour is transparent white, with complex pattern of light, dark, and red-brown spots and stripes. On dorsal side spots and stripes merge and form characteristic striped pattern. Lateral sides of body devoid of stripes but covered with brown spots. Brown branches of digestive gland clearly visible through thin walls of rhinophoral sheathes, dorsal appendages, and velar papillae. Lamellae of rhinophores brown. All body, including rhinophoral sheathes, cerata, and upper parts of foot covered with white and golden pigment spots. Large dots of pigment are often placed inside tubercles on dorsal and lateral surface of body.

Internal morphology ( Figs. 7 View Fig , 8B, C View Fig ): Dorsal process of jaws strong; length about onequarter of jaw body length. Inclined posteriorly at about 15°. Length of dorsal processes of jaws about one-third length of jaw body, strong at base, but becoming transparent and subulate posteriorly. Denticles absent on masticatory border. Radula formula:24 × 9–10.1.9–10 (adult specimen), 17 × 10–11.1.10–11 (subadult specimen). Rachidian tooth large and strong, with quadrangular base and triangular cusp. Rachidian tooth of subadult specimens bear 10–12 small, relatively sharp denticles that continue down dorsal side of cusp as thin furrows. In adult specimens denticles absent, tooth completely smooth, sometimes with faint furrows ( Fig. 7A, B View Fig ). Colour of oldest rachidian teeth is light yellow, others transparent. 9–11 lateral teeth, each consisting of elongate, flattened plate and cusp. Outer border of cusps bear 5–9 sharp and strong denticles. Innermost lateral tooth thin, delicate, and highly denticulated, one or two outermost teeth narrow, thin and flattened and do not bear denticles ( Fig. 7C View Fig ). Reproductivesystemtriaulic ( Fig.8C View Fig ). Largewhiteovotestis composed of many rounded lobules, and leading to hermaphrodite duct that expands into elongate sinuous ampulla. Prostata consists of 7–8 oval alveoli, distal part of vas deferens narrow and winding, expanding to narrow, elongate unarmed penis. Oviduct connects through insemination duct into female gland complex. Vagina long, strait, with small bursa copulatrix, gradually narrows into rounded seminal receptaculum. Long insemination duct emerges from seminal receptaculum and connects into oviduct and female gland mass. Female genital aperture opens posterior to penis on right side of body, between first and second pairs of dorsolateral processes.

Ecology: Found subtidally at 7–16 m in depth. Inhabits brown and red algae or rocks covered with hydrozoan colonies (Thecaphora). Egg masses are unknown.

Distribution: This far, known from Avacha Bay, Kamchatka peninsula ( Ekimova et al., 2015) and from Rudnaya Bay, Sea of Japan (present study).

Remarks: D. kamchaticus was described from Avacha Bay (North-West Pacific, Kamchatka peninsula) at the depth 7–10 m ( Ekimova et al., 2015). Here for the first time this species out of its type locality is described. External and internal morphology of holotype corresponds to our specimens, with a few exceptions. Type specimens of D. kamchaticus are defined by small dorsolateral appendages with short and bulbous primary stalks and small secondary branches and lacking tertiary. Probably it can be related with preserving changes of soft tissues. Radula formula described in Ekimova et al. (2015) is 16–20 × 7–10.1.7–10, while in our specimens it is 17–24 × 9–11.1.9–11. However, it can be explained as intraspecific variations of radular teeth number. Morphology of the rachidian and lateral teeth, jaws and reproductive system is quite similar in type specimens and individuals studied.

It can be concluded that our specimens truly belong to D. kamchaticus according to both morphological and molecular analyses. The first finding of this species in the Sea of Japan extends its known distribution from the boreal regions of Northwestern Pacific to the northern part of the Sea of Japan. Supposedly, this species can be also found in Sakhalin, Kuril Islands and in the Okhotsk Sea.