Dendronotus dudkai, Ekimova & Schepetov & Chichvarkhina & Chichvarkhin, 2016

Dendronotus dudkai View in CoL sp.n.

Figs. 9–11 View Fig View Fig View Fig .

Dendronotus frondosus sensu Baba, 1993 View in CoL non Ascanius, 1774

Type material: Holotype: ZMMU Lc-40364, Sea of Japan, Vostok Bay , Vostok Marine Biological Station, 6–7 m depth, coll. A. Chichvarkhin & A. Goloseyev, 10–15 August 2014 . Paratypes: ZMMU Lc-40365, 1 specimen, Sea of Japan, Vostok Bay, Vostok Marine Biological Station, 6–7 m depth, coll. A. Chichvarkhin & A. Goloseyev, 15 August 2014 ; ZMMU Lc- 40366, 1 specimen, Sea of Japan, Amursky Bay, near the Institute of Marine Biology , 2–5 m depth, coll. K. Dudka, 25 May 2014 ; ZMMU Lc-40367, 2 specimens, Sea of Japan, Vostok Bay, Vostok Marine Biological Station, 10–15 m depth, coll. I. Ekimova & A. Chichvarkhin, 10–15 September 2015 .

Additional material examined:W195, 1 specimen, Sea of Japan, Rudnaya Bay, 10 m depth, coll. A. Chichvarkhin, 10 June 2012; W196, 1 specimen, Sea of Japan, Rudnaya Bay, 10–12 m depth, coll. A. Chichvarkhin, 8 June 2013; W197–W200, 4 specimens, place, depth, date and collectors are the same as W196; W201, 1 specimen, Sea of Japan, Vostok Bay, Vostok Marine Biological Station, 6–7 m depth, coll. A. Chichvarkhin & A. Goloseyev, 10 August 2014; W202, 2 specimens, Sea of Japan, Vostok Bay, Vostok Marine Biological Station, 6–7 m depth, coll. A. Chichvarkhin & A. Goloseyev, 15 August 2014; W207, 3 specimens, Sea of Japan, Vostok Bay, Vostok Marine Biological Station, 6–7 m depth, coll. K. Dudka, 15 March 2015; WS2894–WS2897, 4 specimens, Sea of Japan, Vostok Bay, Vostok Marine Biological Station, 10–15 m depth, coll. I. Ekimova & A. Chichvarkhin, 10–15 September 2015.

Type locality: Sea of Japan, Vostok Bay, Vostok Marine Biological Station, 6–7 m depth, on Obelia cf. longissima (Pallas, 1766) .

Etymology: Dedicated to our friend and invaluable assistant Mr. Konstantin Dudka, stuff diver of Institute of Marine Biology RAS (Vladivostok), one of the first collectors of this species.

Description. External morphology ( Figs. 9 View Fig , 11A View Fig ): Body elongate, laterally compressed.Foot narrow, tail short. Oral veil small with 6–12 large, secondary branched cerata. Muscular lips with 5–10 short lip papillae.Rhinophoral sheaths with long stalk and 4–5 crown secondary branched appendages. Lateral papillae moderate in size with small secondary branches. Rhinophores with 8–10 lamellae. 6–8 pairs of highly branched dorsolateral processes, size and degree of branching decrease towards the tail. 2–5 primary stalks on each cerata, branching pattern “rosette” ( Fig. 11A View Fig ). Secondary branches long and rounded, tertiary branches short and sometimes pointed. Digestive gland diverticula penetrate cerata and rhinophoral sheath processes. These diverticula in first pair of cerata and rhinophores originate from anterior lobe of digestive gland; others arise from posterior lobe. Cardiac prominence slightly raised. Body covered with conical papillae that usually tallest on cardiac prominence. Anal opening on right side of body about midway between first and second pair of dorsolateral processes. Reproductive openings lateral, below first pair of dorsolateral processes on right side.

Colour ( Fig. 9 View Fig ): General colour pattern varies from beige to dark-brown. Background colour translucent-white or light yellow. A lot of spots, stripes and dots on dorsal side of the body, cerata, rhinophoral sheath processes and upper parts of foot. Their colour varies from yellow to dark-brown. Some specimens covered with dots of golden or white opaque pigment. This pigment locates also in low body papillae and small turbecles. All specimens possess well-visible white stripes between pairs of cerata. Digestive gland diverticula can be seen through transparent body wall. Digestive gland beige or brown. The colour of the rhinophores similar to body colour.

Internal morphology ( Figs. 10 View Fig , 11B–D View Fig ): Dorsal processes of jaws about 2.5 times shorter than jaw body ( Fig. 11B View Fig ). Inclined posteriorly at about 45°. Masticatory process about one-third as long as jaw body, slightly curved at base and become transparent and subulate posteriorly. Masticatory border with a single raw of denticles ( Fig. 10G View Fig ). Radula formula: 32 × 7–8.1.7– 8 (W203); 27 × 6–7.1.6–7 (W201), 29 × 8– 9.1.8–9 (W196) ( Fig. 10A–D View Fig ). Rachidian tooth strong, triangular, length same as width, bears 12–18 sharp denticles with thin furrows on both sides of the reduced cusp ( Fig. 10E View Fig ). Lateral teeth slightly curved toward midline, bear 4–8 well-defined denticles ( Fig. 10F View Fig ). Outermost lateral teeth form varies from flattened shape to narrow with pointed apex. Innermost lateral teeth thin and highly denticulated. Reproductive system triaulic ( Fig. 11C, D View Fig ). Ovotestis large and white, composed from number of rounded lobules, leads to hermaphrodite duct. Ampulla wide and sinuous, merging with oviduct and connecting into prostate. Prostate concentric ring-shaped, consists of 12–14 oval alveolar glands. Distal part of vas deference winding expand into wide, muscular portion. Penis slightly curved, lacking armature. Oviduct connects through insemination duct into female gland complex. Vagina long, convoluted, narrows into rounded seminal receptaculum and then connects into oviduct and female gland mass. Small bursa copulatrix near proximal part of vagina, Female genital aperture opens posterior to penis on right side of body, between first and second pairs of dorsolateral processes.

Рис. 10. Dendronotus dudkai sp.n., микрофотографии участков радулы и жевательной поверхности челюстей (СЭМ). A — W201, центральные и латеральные Зубы; B — W203, центральные и латеральные Зубы; C — W202, центральные и внутренние латеральные Зубы, D — W197, центральные и латеральные Зубы; E — W197, центральный Зуб; F — W197, латеральные Зубы; G — жевательный отросток челюстей, жевательнаЯ поверхность несет одинарный рЯд Зубчиков. МасШтаб: A, B, F — 50 мкм; C — 20 мкм; D — 80 мкм; E — 10 мкм; G — 100 мкм.

Ecology: Found subtidally at 2–16 m in depth. Feeds on tecaphoran hydrozoan colonies of the family Campanulariidae ( Obelia cf. longissima ). These colonies occupied artificial substrates (ropes) only; we never found them with Dendronotus spp. on natural substrates. Reproduction period in June–July. Egg mass is narrow white cord, coiled on hydrozoan colonies.

Distribution: the Sea of Japan: from Rudnaya Bay to Amursky Bay, Sado Isl. Probably has wider distribution.

Remarks:

The differences between D. dudkai sp.n. and D. primorjensis were discussed above. The individuals of D. dudkai sp.n. have very similar internal and external morphology with eastern Pacific species D. venustus and amphiboreal D. frondosus . Nevertheless, an array of diagnostic differences can be designated in these three species. In contrast with D. dudkai sp.n., D. venustus possesses unbranched papillae of rhinophoral sheath, very large outgrowth of cardiac prominence, the ampulla is crescent-shaped. D. frondosus is distinguished from D. dudkai sp.n. by absence of denticles on the masticatory process of jaws, elongated shape of rachidian teeth, flattened shape of outer lateral teeth with no cusp; the ampulla D. frondosus is rounded, prostate contains more alveoli (16–40). According to morphological cladistic analysis by Stout et al. (2010), morphological differences shown above are sufficient for species delimitation.

Similar colour pattern and morphology is specific also to D. kamchaticus , D. kalikal as well as some colour variations of D. lacteus . Nevertheless these species differ from D. dudkai sp.n. in radular morphology. The rachidian tooth in D. kamchaticus is smooth, denticles and furrows are absent. D. kalikal possesses elongated rachidian tooth bearing tiny denticles along external edge, although the number of denticles is lower while furrows are very fine and nearly invisible. Rachidian tooth in D. lacteus possesses large number of small denticles, their furrows are fine, lateral teeth are triangle shaped with small proximal denticles; some individuals are lacking denticles.

The rachidian tooth of D. dudkai sp.n. radula possesses well-developed denticles that lengthen with deep furrows; conical cusp is reduced. This pattern of features distinguishes this species from D. dalli , D. kamchaticus , D. niveus (possessing smooth rachidian tooth), D. robustus , D. patricki , D. iris (developed conical cusp), D. rufus , D. lacteus , D. kalikal , D. albus , D. gracilis (denticle furrows more or less reduced till complete disappearance), D. subramosus (sporadic denticles and furrows), D. albopunctatus (furrows approach central part of the teeth). Teeth shape in D. dudkai sp.n. is well distinguished form D. noachi and D. regius — spacing between margins in these two species increases toward the cusp. Rachidian tooth in D. dudkai sp.n. is similar to D. venustus , D. frondosus , D. comteti , D. orientalis . As said above, both D. frondosus and D. venustus differ from D. dudkai sp.n. with the features of internal and external morphology. D. comteti possesses elongated rachidian tooth and lower number of lateral ones (4–5). Besides that, this species possesses lower number of dorsolateral appendages (2–4 pairs), with no secondary branching. The number of lateral teeth in D. orientalis (2) is a good diagnostic trait to be distinguished from D. dudkai sp.n.