Dendronotus robustus Verrill, 1870

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 : 128

Dendronotus robustus Verrill, 1870

Fig. 7

Dendronotus robustus Verrill, 1870: 405 ; Lundin et al., 2017: 303, 306, 309–315, Figs 3 , 4 .

Non auct., not Ekimova et al. (2015) (mix-up with D. velifer G.O. Sars, 1878 ).

Extended diagnosis. Body wide. Six to seven pairs of branched dorsolateral appendages. 10 to 15 appendages of oral veil. Four to five appendages of rhinophoral stalks. Lateral papilla of rhinophoral sheaths absent. Rhinophores with 7–14 lamellae. More than 20 lip papillae. Basal colour light grayish to yellowish with scattered opaque white and yellow spots. Dorsal processes of jaws inclined posteriorly at approximately 47° to the longitudinal axis of the jaw body and 0.55 of its length. Masticatory processes apparently bear denticles (may possess ridgelike structures). Radula with upto 31 rows of teeth. Central tooth with high cusp and up to 20 small distinct denticles without furrows. Up to nine lateral teeth with up to seven denticles. Ampulla moderately narrow, with approximately three to four irregular loops. Bursa copulatrix moderate in size, rounded to pear-shaped,withsmallseminalreceptaculum placed distally near the vaginal opening. Prostate discoid with about 10 alveolar glands. The vas deferens is moderate in length, penis massive, broad, slightly curved. Bodylength of verified specimens up to 50 mm.

Distribution. North Atlantic (both western and eastern, Canada, Norway, Russia and USA), very shallow waters only, in the Arctic, the

range does not extend further eastward than the Barents Sea.

Bathymetry. Intertidal to less than 20 m deep.

Remarks. T.A. Korshunova’s and A.V. Martynov’s pre-2015 analysis has showed that there are at least two species in the “ D. robustus complex”, namely D. robustus Verrill, 1870 and D. velifer G.O. Sars, 1878 . However, this analysis was unfortunately not included in the final version of the publication by I.A. Ekimova ( Ekimova et al., 2015). This detailed morphological and molecular analysis has shown that D. robustus and D. velifer are well differentiated morphologically, bathymetrically and according to the molecular analysis ( Lundin et al., 2017). In the previous literature these two species have been mixed.

Figures

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 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