Dendronotus bathyvela

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

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Dendronotus bathyvela

sp. nov.

Dendronotus bathyvela  sp. nov.

( Figures 4View FIGURE 4, 5CView FIGURE 5) 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. KomatsuGoogleMaps  . 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. FujitaGoogleMaps  . 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.GoogleMaps  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. SaitoGoogleMaps  . 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. SaitoGoogleMaps  . 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. SaitoGoogleMaps  .

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. 4View FIGURE 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. 4View FIGURE 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 DView FIGURE 4).

The jaws are ovoid with strong dorsal processes, denticles present ( Fig. 4View FIGURE 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. 4GView FIGURE 4). Lateral teeth are long, slightly curved, commonly completely smooth or bearing few (up to 2) weak denticles ( Fig. 4HView FIGURE 4).

Reproductive system triaulic ( Fig. 5CView FIGURE 5), ampulla folded several times ( Fig. 5CView FIGURE 5, am), prostate consisting of 21–25 alveolar glands ( Fig. 5CView FIGURE 5, pr), vas deferens long ( Fig. 5CView FIGURE 5, vd) expanding to elongate penial sheath ( Fig. 5CView FIGURE 5, psh), penis very long, thin ( Fig. 5C, pView FIGURE 5), vagina very long and considerably twisted ( Fig. 5CView FIGURE 5, vg), bursa copulatrix is large, rounded, and elongated ( Fig. 5CView FIGURE 5, bc) with small seminal receptaculum placed distally ( Fig. 5CView FIGURE 5, 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. 4View FIGURE 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. 4DView FIGURE 4); 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).


Tavera, Department of Geology and Geophysics