Dendronotus dalli sensu Bergh 1886

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.