Dendronotus lacteus

Dendronotus lacteus (Thompson, 1840)

Fig. 7

Tritonia lactea Thompson, 1840: 88–89, Pl. 2, Fig. 3.

Dendronotus lacteus Eliot, 1910: 161; Nordsieck, 1972: 68; Pruvot-Fol, 1954: 356; Thollesson, 1998: 191–193, Figs 1–3; Evertsen and Bakken, 2005: 18; Korshunovaet al., 2017: 2–7, Figs 1, 2.

not Becher, 1886: 14.

not Eliot, 1910:112 (= D. dalli).

= D. frondosus auct. non Ascanius, 1774.

Extended diagnosis. Body relatively narrow. Four to eight pairs of branched dorsolateral appendages which in adults commonly show specific “curly” patternthoughotherspecimens with more “typical” for genus Dendronotus elongated appendages may occur. Four to ten oral veil appendages. Four to six appendages (inetrnal middle and posterior ones longest) of rhinophoral stalks. Lateral papilla of rhinophoral sheaths present. Rhinophores with 10–14 lamellae. At least more than 15 lip papillae.Basalcolourfromuniformlydarkredto uniform white, often with small brownish dots. Redddish and brownish specimens may have white stripes between cerata, white specimens milky, non-transparent in appearance. Dorsal processes of jaws inclined posteriorly at approximately 55–60° to the longitudinal axis of the jaw body and 0.52 of its length. Masticatory processes possibly bear denticles and ridge-like structures. Radula with up to 43 rows of teeth. Central tooth with up to 40–50 small denticles (commonly smaller), often with peculiar ribs, never completely smooth. Up to 16 lateral teeth with up to five denticles. Ampulla moderately narrow with several windings or folded loops. Bursa copulatrix large, rounded to oval. Seminal receptaculum small placed distally at considerable distance from the vaginal opening. Prostate discoidwith a range from 12 to morethan 30 alveolar glands. The vas deferens is relatively long in length, penis relatively long, bent. Body length up to 150 mm.

Distribution. North Atlantic and Arctic (eastern limit at least Laptev Sea, Russia).

Bathymetry. From circa 5 to 427 m depth; commonat shallow, subtidal depthsat around 10– 20 m.

Remarks. Dendronotus lacteus together with D. frondosus and D. europaeus form a species complex that is difficult to distinguish based on external characteristics, but in which it is still possible to find fine-scale morphological differences. In contrast, the radulae of these three species demonstrate distinctly different patterns (Korshunova et al., 2017b).