Dendronotus dalli Bergh, 1879, 1886

Korshunova, Tatiana, Bakken, Torkild, GrØtan, Viktor V., Johnson, Kjetil B., Lundin, Kennet & Martynov, Alexander, 2021, A synoptic review of the family Dendronotidae (Mollusca: Nudibranchia): a multilevel organismal diversity approach, Contributions to Zoology 90 (1), pp. 93-153 : 115-116

Dendronotus dalli Bergh, 1879

Fig. 7

Dendronotusdalli Bergh, 1879: 94 , Pl. 1, Fig. 21; Pl. 2, Figs 9–12; Pl. 3, Figs 2–6 ; Robilliard, 1970: 452–455, Figs 13–15; McDonald, 2009: 463 (bibliography); Martynov & Korshunova, 2011: 155–157 (verified photographs of living specimens, description and biology in NW Pacific); Ekimova et al., 2015: 860–863, Figs 6C , 8G , 11, 12, 13A.

Dendronotusfrondosus var. dalli Bergh, 1879 – Odhner, 1907: 19.

Not D.dalli sensu Bergh, 1886 , Knipowitsch, 1902, Roginskaya, 1987 (= D. elegans Verril, 1880 ).

Extended diagnosis. Body relatively narrow. Four to eight pairs of branched dorsolateral appendages. Four to five appendages of oral veil. Four to 12 appendages (equal in size or few posterior ones longer) of rhinophoral stalks. Lateral papilla of rhinophoral sheaths present. Rhinophoreswith 16–33 lamellae. Lip papillae 15–40 (and more). Basal colour uniform translucent gray, light yellow to orange, brownish or pinkish, with external opaque white pigment on tips of dorsolateral appendages. Dorsal processes of jaws inclined posteriorly at approximately 60° to the longitudinalaxisof thejawbodyand0.45 of its length. Masticatory processes apparently bear denticles (may possess ridge-like structures). Radula with up to 51 rows of teeth. Central tooth completely smooth in adults. Up to 16 lateral teeth with up to 19 denticles. Ampulla relatively narrow with several (at least three) loops. Bursa copulatrix very large, oval. Seminal receptaculum small placed distally at a moderately short distance from the vaginal opening. Prostate discoid with up to 50 (and more) alveolar glands. The vas deferens is moderate in length, penis large, wide, with a blunt tip. Body length upto 14 cm.

Distribution. North Pacific (The Seaof Japan inthe west and atleast Washington State, USA in the east to at least Chuckchii Sea; Russia, in the Arctic (may possibly penetrate further to the west in the Arctic).

Bathymetry. Verified records from 5 to 50 m depth.

Remarks. Until recently, the North Atlantic D. elegans (see below) has been confused with the North Pacific D. dalli . The best external feature to distinguish these two closely related species is the presence of an external opaque white pigment on the apical parts of the dorsolateral processes in D. dalli , whereas in D. elegans such a pigment, if present, is internal. These species may co-occur in some Arctic localities, but this needs to be further investigated. For D.dalli an absence of tertiary branches of the dorsolateral appendages was incorrectly mentioned by Ekimova et al. (2015).Thereisapossibilitythatlight-coloured varieties of D. kamchaticus were depicted under D.dalli , judging fromphotographs infor example Behrens (1980) (see also Korshunova et al., 2016a). In some studies, Dendronotus dalli was incorrectly considered a synonym of D. frondosus ( Odhner, 1936; MacFarland, 1966) due to an underestimation of the importance of ontogenetic radula data (central teeth are denticulated in juveniles and usually smooth in adults).

We have investigated a considerable number of specimens and sequences of D. elegans from the North Atlantic and neighbouring subarctic regions. There are no confirmed records of true D. dalli in the North Atlantic and neighbouring regions. The indication of D. dalli fromthe North Atlantic (Genbank COI AF249800 ) in a table of the paper of Wollscheid-Lengeling et al. (2001) is due to a mix-up of localities, inthiscase withthe North Pacific. The same can be said about Cadlina luteomarginata from the North Atlantic in the same paper ( Wollscheid-Lengeling et al., 2001) for which Johnson (2010: 142) explained that they originated from the North Pacific.

Figures

FIGURE 2 Phylogenetic relationships of the species of the genera Dendronotus, Pseudobornella and Cabangus in single COI, 16S, 28S, and H3 gene trees inferred by Bayesian Inference (BI). Some branches are collapsed. Positions the Pseudobornella orientalis highlighted green; positions the Cabangus regius highlighted orange.Numbers represent posterior probabilities from BI. PHOTOGRAPHS BY A. MARTYNOV AND T. KORSHUNOVA

FIGURE 3 A.Map of the Northern Hemisphere showing the distribution of D.elegans (including “D.niveus”), D.kalikal, and D.yrjargul sp. nov.The type locality of D.elegans is indicated by crossed lines. B. The haplotype networks based on cytochrome c oxidase subunit I (COI), 16S rRNA (16S), and 28S rRNA (28S) molecular data showing genetic mutations occurring within D.elegans (“D.niveus”), D. kalikal, and D.yrjargul sp. nov. specimens.Abbreviations:BeSt – Bering Strait; BS – Barents Sea; Gr – Greenland; Km – Kamchatka; KS – Kara Sea; Ku – Kuril Islands; LS – Laptev Sea; Nf – Newfoundland; NS – Norwegian Sea; WS – White Sea.Type locality of D.elegans is marked on the map by “x”.

FIGURE 4 Dendronotus yrjargul sp.nov.(a–n) and D.kalikal (o–t), external and internal morphology.a–c: living holotype of D.yrjargul NTNU-VM-76306 (a) and its habitat (b, c), dorsal,ventral and lateral views with egg mass and associated hydroid Abietinaria fusca, respectively; d: Dendronotus yrjargul, habitat of living paratype NTNU-VM-76302;e: jaw of holotype; f:denticles on the masticatory edge of the holotype; g: jaws of paratype NTNU-VM-76302; h:discoid ridge-like structures on the masticatory edge of paratype NTNU-VM-76302;i: details of discoid structures on the masticatory edge of paratype NTNU-VM-76302; j: anterior part of radula of holotype; k:central teeth of radula of holotype;l:lateral teeth of radula of holotype; m:central teeth of radula of paratype NTNU-VM-76302; n: lateral teeth of radula of holotype; o: living holotype of D.kalikal; p: jaw of D.kalikal, specimen from Kurile Islands;

FIGURE 5 Dendronotus nordenskioeldi sp. nov.ZMMU Op-665, external and internal morphology.a–b:living holotype, dorsal and lateral views respectively;c:ventral view of preserved holotype;d: jaw of holotype; e: irregular denticles on the masticatory edge of the holotype;f:posterior part of radula; g:central teeth of radula; h: lateral teeth of radula of holotype.Scale bars: d: 1mm; e: 20 µm; f:100 µm; g, h: 30 µm. PHOTOGRAPHS BY O. ZIMINA (A, B) AND T. KORSHUNOVA (C). SEM MICROGRAPHS BY A. MARTYNOV

FIGURE 6 Reproductive systems. a, Dendronotus yrjargul sp. nov.; b, D.kalikal; c, D.elegans; d, D. nordenskioeldi sp. nov. Scale bars:a–d 1mm.Abbreviations:am, ampulla; bc, bursa copulatrix; fgm, female gland mass; fo, female opening; p, penis; pr, prostate; rs, receptaculum seminis; ud, uterine duct; vd, vas deferens; vg, vaginal duct.

FIGURE 7 Representaives of the genus Dendronotus (living specimens). PHOTOGRAPHS BY T. KORSHUNOVA, A. MARTYNOV, K. FLETCHER, D. MILLER, Y. FUJIWARA, K. HASEGAWA, K. SANAMYAN, N. SANAMYAN, AND O. ZIMINA

FIGURE 8 Dendronotus elegans. External and internal morphology.a: living specimen ZMMU Op-713 from Greenland, near East Atlantic North American coast; b: jaw, same specimen; c; posterior part of radula, general overview,same specimen; d: close up of smooth central teeth, same; e: close up of lateral teeth, same; f:living specimen ZMMU Op-714 (as “D.niveus”) from the White Sea (subarctic); g: jaw, same specimen; h:masticatory edge of the jaws,same; i: posterior part of radula, general overview,same specimen; j: close up of smooth central teeth, same; k: living specimen ZMMU Op-715 from the Laptev Sea (Arctic); l: jaw, same specimen; m: posterior part of radula, close up of smooth central teeth, same; n: lateral teeth, same.o: discoid prostate with numerous alveols (which considerably exceed the considerably underestimated number presented in the first description of D.niveus), same specimen; Scale bars: b, l, 1mm; c: 300 µm; d, h–j, m: 100 µm; g: 1000 µm; e, n: 30 µm. PHOTOGRAPHS BY O. ZIMINA (A, K) AND T. KORSHUNOVA (F). SEM MICROGRAPHS BY A. MARTYNOV