Dendronotus elegans Verrill, 1880

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 : 116-118

Dendronotus elegans Verrill, 1880

Figs 7 , 8

Dendronotuselegans Verrill, 1880: 385–386 .

Dendronotus “elongatus”: Roginskaya, 1987: 175 (lapsus calami for D. elegans Verrill, 1880 ).

Dendronotus niveus Ekimova, Korshunova, Shepetov, Neretina, Sanamyan & Martynov, 2015: 864–869 , Figs 6D , 8F , 13B, 14, 15 syn. nov.; Valdés et al., 2017: 6–7, 4B, 5B.

Dendronotusdalli sensu Bergh, 1886 (non Bergh, 1879); Robilliard, 1970: 452; Bleakney, 1996: 109 ( D. elegans incorrectly mentioned as synonym of D. dalli ).

Extended diagnosis. Body relatively narrow. Five to ten pairs of branched dorsolateral appendages. Six to nine appendages of oral veil. Four to five appendages (equal in size or few posterior ones longer) of rhinophoral stalks. Lateral papilla of rhinophoral sheaths present. Rhinophoreswith 8–23 lamellae. Lip papillae 8–50. Basal colour uniform, pinkish to light orange, with internal opaque white pigment of tips of dorsolateral appendages. Dorsalprocessesof jawsinclinedposteriorly at approximately 40° to the longitudinal axis of thejawbodyand 0.43of itslength.Masticatory processes apparently bear denticles (which may possess ridge-like structures). Radula with up to 42 rows of teeth. Central tooth completely smooth in adults. Up to at least 13 lateral teeth with up to eight denticles (can be more). Bursa copulatrix large, oval. Seminal receptaculum small placed distally at a moderately short distance from the vaginal opening. Prostate discoid with up to 60 and more alveolar glands (their number was considerably underestimated in the original description of its new synonym D. niveus (see remarks below). The vas deferens is moderate in length, penis strong, conical. Body length upto 70 mm.

Distribution. North Atlantic (known southern limit – Cape Cod, USA) to the Arctic (including Barents Sea and White Sea, known northeastern limit is the Laptev Sea, Russia).

Bathymetry. 10–25 m (WhiteSea) to 258 m depth (western North Atlantic).

Remarks. Ekimova et al. (2015) overlooked important details in the original description of D. elegans Verrill, 1880 , for which a big animal with uniform salmon-coloured body was used, and a special mentioning was made of the completely smooth central teeth (Verrill, 1880: 385–386). These characters are identical to those of the recently described D. niveus Ekimova et al., 2015 . The available molecular data ( Valdés et al., 2017; present study, figs 1–3) also show that specimens identified as D. niveus from off the east coast of North America (relatively close to the type locality of D. elegans ) are identical to specimens from the type locality of D. niveus in the White Sea. The holotype of D. elegans in the Smithsonian Institution ( NMNH, 2020) is not suitable for molecular study. However, a microslide with radula of the holotype is

kept separately in the Yale Peabody Museum of Natural History (YPM IZ 010761.GP) and available as online images ( Yale Peabody Museum, 2020), which confirm the presence of massive smooth central teeth. The date (6September1879),thedepth (26fathoms =48 meters) and locations (Stellwagen Bank, off Cape Cod) for collecting data of the holotype of D. elegans exactly match radula YPM IZ 010761.GP, the preserved body USNM 842116 and the original description of D. elegans in Verrill (1880). Additional morphological information of the molecularly investigated specimens of D. elegans of the present study is given in fig. 8. It is evident that specimens from the Atlantic North American coast and from the Arctic Eurasian regions are morphologically similar according to their external and internal features. We therefore synonymize Dendronotus niveus Ekimova et al., 2015 with D. elegans Verrill, 1880 . Another species with smooth central teeth at the adult stage is D. dalli Bergh, 1879 (see above, figs 1, 2), but this one is found predominantly in the North Pacific and differs from D. elegans in habitus morphology (apical parts of dorsolateral appendages with external opaque white pigment vs. with internal or absent white pigment in D. elegans ) and molecular data.

Figures

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