Dendronotus bathyvela, Martynov & Fujiwara & Tsuchida & Nakano & Sanamyan & Sanamyan & Fletcher & Korshunova, 2020

Martynov, Alexander, Fujiwara, Yoshihiro, Tsuchida, Shinji, Nakano, Rie, Sanamyan, Nadezhda, Sanamyan, Karen, Fletcher, Karin & Korshunova, Tatiana, 2020, Three new species of the genus Dendronotus from Japan and Russia (Mollusca, Nudibranchia), Zootaxa 4747 (3), pp. 495-513 : 507

Dendronotus bathyvela sp. nov.

( Figures 4 , 5C )

http://zoobank.org/ 28A36F6D-C221-4C34-B40A-631E3129B943

Type material. Holotype, NSMT-Mo 94455, 45 mm long preserved, dissected, Japan, Tohoku, off Ofunato, Iwate Prefecture, 38° 53.5’ N 142° 2.8’ E, 18.10.2007, depth 303–307 m, collector K. Hasegawa, H. Komatsu . Three paratypes, NSMT-Mo 94450, 25, 26, 27 mm long (preserved), Japan, Tohoku , off Shimokita Peninsula , Aomori Prefecture, 41° 0.5’ N 141° 2.0’ E, 10.10.2006, depth 511– 510 m, collector T. Kuramochi, T. Fujita . Paratype, NSMT- Mo 94452, 35 mm long (preserved), Japan, Tohoku, off Kinkazan , Miyagi Prefecture, 38° 23.2’ N 141° 58.2’ E, 04.11.2006, depth 305–309 m, collector H. Komatsu. Paratype, NSMT-Mo 93078, 35 mm long (preserved), Japan, Tohoku, off Kesennuma , Miyagi Prefecture, 38° 4.6’ N 141° 55.3’ E, 19.11.2005, depth 249 m, collector T. Fujita, H. Saito . Paratype, NSMT-Mo 93080, 21 mm long (preserved), Japan, Tohoku, off Kesennuma , Miyagi Prefecture, 38° 4.2’ N 141° 58.9’ E, 19.11.2005, depth 306–309 m, collector T. Fujita, H. Saito . Paratype, NSMT-Mo 93061, 14 mm long (preserved), Japan, Tohoku, off Kinkazan , Miyagi Prefecture, 38° 2.3’ N 142° 2.1’ E, 17.11.2005, depth 382– 376 m, collector T. Fujita, H. Saito .

Type locality. Japan, off the Pacific coast of Northern Honshu .

Etymology. From Ancient Greek βάθος (deep sea) + velum (veil) in reference to the deepest record so far known of this wide-bodied Dendronotus species with a broad oral veil.

Diagnosis. Body broad, 6–7 pairs dorsolateral appendages, colour dull reddish-brownish with numerous white spots, central tooth with well-defined denticles and furrows, vas deferens moderate in length, penis long, very thin.

Description. Body broad, up to 45 mm in length ( Fig. 4 A–D), 10–15 long branched appendages of oral veil, 5 appendages of rhinophoral stalks, 15–25 rhinophoral lamellae, branched rhinophoral lateral papilla absent, 6–7 pairs dorsolateral appendages (including smallest posterior ones), ca. 50–70 lip papillae. Dorsolateral appendages with moderate primary stalk, moderately branched secondary branches, and elongated tertiary branches ( Fig. 4 A–D). Reproductive and anal openings placed laterally on right side. General colour dull reddish-brownish with numerous distinct opaque white dots on notum, tips of lateral appendages, oral appendages ( Fig. 4 D ).

The jaws are ovoid with strong dorsal processes, denticles present ( Fig. 4 E–F). Masticatory processes apparently bear ca 60 denticles. Radula formula is 36 × 1–13.1.13–1 (paratype 21 mm), 41 × 1–12.1.12–1 (paratype 27 mm), 37 × 1–13.1.13–1 (paratype 35 mm), 36 × 1–14.1.14–1 (holotype 45 mm). Central tooth with broad, relatively low cusp, strongly denticulated and bearing up to over 30–35 distinct to small denticles ( Fig. 4G ). Lateral teeth are long, slightly curved, commonly completely smooth or bearing few (up to 2) weak denticles ( Fig. 4H ).

Reproductive system triaulic ( Fig. 5C ), ampulla folded several times ( Fig. 5C , am), prostate consisting of 21–25 alveolar glands ( Fig. 5C , pr), vas deferens long ( Fig. 5C , vd) expanding to elongate penial sheath ( Fig. 5C , psh), penis very long, thin ( Fig. 5C, p ), vagina very long and considerably twisted ( Fig. 5C , vg), bursa copulatrix is large, rounded, and elongated ( Fig. 5C , bc) with small seminal receptaculum placed distally ( Fig. 5C , rs).

Biology. Inhabits sand and muddy substrates with stones.

Distribution. Presently known only off the Pacific coast of Northern Honshu ( Japan), at depths of 249– 510 m.

Remarks. According to the morphological data Dendronotus bathyvela sp. nov. clearly belongs to the group of wide-bodied Dendronotus species, which includes only a few species, i.e. D. patricki , D. robustus and D. velifer . Because all available D. bathyvela sp. nov. were formalin-fixed, this prevented us from including this species in the molecular phylogenetic analysis. However, the present morphological data are enough to distinguish D. bathyvela sp. nov. from all other wide-bodied species of the genus Dendronotus . The abyssal NE Pacific species, D. patricki , readily differs from the bathyal NW Pacific D. bathyvela sp. nov. by its uniform pinkish colouration (white pig- ment presents only on apices of dorsolateral and velar appendages, but not on the body) and details of the radula ( Stout et al., 2011). Particularly, in D. patricki the number of lateral teeth is up to eight, whereas in D. bathyvela sp. nov. —up to 14. The number of lateral denticles on the central teeth is about 20 in D. patricki , whereas in D. bathyvela sp. nov. there are over 30 denticles. Previously, D. robustus had been recorded from the Sea of Japan and the Pacific side of Honshu ( Roginskaya 1997; Hasegawa 2009). However, the true D. robustus from the shallow waters of the North Atlantic (see Lundin et al. 2017) considerably differs from the North Pacific material in the details of colouration and the radula. For a long time, D. velifer from Northern Europe and the Arctic was also confused with D. robustus , however recently it was shown that this is a distinct species, according to both morphological and molecular data ( Lundin et al. 2017). The following differences between D. velifer and D. bathyvela sp. nov. are: 1) Appendages of the oral veil in living specimens of D. velifer are distinctly shorter than in living D. bathyvela sp. nov. ( Fig. 4 A–D); 2) Large specimens of D. velifer commonly bear not more than four main dorsolateral appendages (an exceptionally large specimen was reported as having up to five main appendages plus a sixth smaller one), whereas even moderately sized D. bathyvela sp. nov. possess up to six main dorsolateral appendages (plus a seventh smaller one); 3) Colouration of living specimens of D. velifer is bright reddish, whereas D. bathyvela sp. nov. is dull reddish-brownish ( Fig. 4D ); 4) Number of denticles on the central teeth of D. velifer is commonly less than 30, whereas in D. bathyvela sp. nov. it reaches over 30; 5) Number of radular rows in D. velifer is up to 36, whereas in D. bathyvela sp. nov. the number of rows is up to 41 and more. It is remarkable that the North Atlantic shallowwater species D. robustus has up to seven dorsolateral appendages, like the NW Pacific shelf to bathyal new species D. bathyvela sp. nov., but not like the true predominantly Arctic shelf species D. velifer , which commonly has only four dorsolateral appendages. This feature readily distinguishes D. bathyvela sp. nov. from D. velifer . At the same time, D. bathyvela sp. nov. is well-distinguished from D. robustus by the shape of the central radula and external colouration. Bathymetrically D. velifer is known from relatively shallow waters with a range commonly ca. 15–230 m, whereas D. bathyvela sp. nov. inhabits the low part of the continental shelf (not shallower than 249 m) to upper bathyal (510 m) depths. True North Atlantic D. robustus is in turn exclusively a shallow water species and was not recorded deeper than 20–30 m (see Lundin et al. 2017). This set of several complex morphological and ecological features allow us to distinguish D. bathyvela sp. nov. from D. velifer . Recently a deep-sea (but not wide-bodied) species, D. claguei, was described ( Valdés et al. 2018) off the NE Pacific coast. D. claguei fundamentally differs from D. bathyvela sp. nov. by its uniform translucent white colour, elongate body shape, radular details, and in addition D. claguei inhabits upper abyssal depths (2369 m) and not shelf to upper bathyal depths (249–510 m) as D. bathyvela sp. nov. does. In addition, the NE Pacific shallow-water species D. albopunctatus Robilliard, 1972 is somewhat similar to the wide-bodied species group of the genus Dendronotus , but has fewer, and longer, oral veil appendages, lacks lip papilla and considerably differs by the presence of distinct denticulation on the lateral teeth of the radula ( Robilliard, 1972).

Figures

FIGURE 4. Dendronotus bathyvela sp. nov. Holotype, NSMT-Mo 94455, length 45 mm (preserved), Tohoku, off Ofunato, 307 m. A–C. Dorsal, ventral and lateral views respectively, preserved holotype. D. Live holotype. E. Jaws, SEM; F. Masticatory processes of jaws, SEM; G. Radula, posterior part; H. Lateral teeth, posterior part. Scale bars: E, 1000 mm, F, 30 μm, G, 300 μm, H, 100 μm. Photos: Alexander Martynov (A–C, E–H); D, from Hasegawa (2009: fig. 444A) with permission.

FIGURE 5. Reproductive systems. A. Dendronotus jamsteci sp. nov. B. Dendronotus zakuro sp. nov. C. Dendronotus bathyvela sp. nov. Abbreviations: am, ampulla; bc, bursa copulatrix; fgm, female gland mass; fo, female opening; p, penis; pr, prostate; psh, penial sheath; rs, receptaculum seminis; ud, uterine duct; vd, vas deferens; vg, vaginal duct. Scale bars: 1mm.