Dendronotus venustus MacFarland 1966

Dendronotus venustus MacFarland, 1966 Fig. 7 Dendronotusvenustus MacFarland, 1966: 271– 275, Pl. 40, Fig. 2; Pl. 46, Figs 9–12; Pl 47, Figs 1, 2; Pl. 49, Fig. 6; Pl. 50, Fig. 3; Pl. 52; Figs 3–6; Stout et al. 2010: 7. D. frondosus sensu Robilliard, 1970 and auctorum non Ascanius, 1774. Diagnosis. Body narrow. Four to eight pairs of branched dorsolateral appendages. Four to eight appendages of oral veil. Four to six appendages (posterior and medial ones longest) of rhinophoral stalks. Lateral papilla of rhinophoral sheaths present. Rhinophores with 8–14 lamellae. Lip papillae absent or up to eight. Colour forms include white specimens with yellow spots and brownish or reddish specimens with yellow dots and/or tubercles or large amount of white pigment, but with no white-tipped appendages. Dorsal processes of jaws inclined posteriorly at approximately 55–60° to the longitudinal axis of the jaw body and 0.41 of its length. Masticatory processess with ridge-like structures and smaller denticles. Radula with up to 48 rows of teeth. Central tooth with up to 12 small distinct denticles with furrows. Up to eight lateral teeth with up to five denticles. Ampulla voluminous, folded. Bursa copulatrix large, pear-shaped. Seminal receptaculum small placed distally at considerable distance from the vaginal opening. Prostate discoid with few (5–12) alveolar glands. The vas deferens is long, possibly also partly prostatic since thickened on considerable length and then distally narrowed, penis thin, long. Body length upto 42 mm. Distribution. NE Pacific, Canada and USA. Bathymetry. Common in shallow waters, at depths of circa 5– 20 m. Remarks. Despite MacFarland’s (1966) detailed description of D. venustus, it was almost universally considered a synonym of D. frondosus (Robilliard, 1970; McDonald, 1980; Behrens & Hermosillo, 2005) until molecular data showed that it is distinct from D. frondosus (Stout et al., 2010; Korshunovaet al., 2019b). Robilliard (1970) did not doubt the synonymy of D. venustus, although he rarely observed morethan 12 of the prostatic alveolar glands in the NE Pacific specimens, whereas in true D. frondosus their number is usually up to at least 30. There are also minor differences in the radular patterns and some details of colouration between D. frondosus and D. venustus (e.g., common presence of white forms with small yellow spots in D. venustus). Thereis a possibility of the presence of hidden diversity within D. venustus. However, a specimen from Alaska included in our present study (fig. 7) matches the original description of D.venustus verywellbyexternalandinternal features (MacFarland, 1966: 271–275, pl. 40 fig. 2, pl. 46, fig. 9, pl. 50 fig. 3). These characters include the presence of yellow-greenish spots on a greyish to whitish body, a specifically broadened, somewhat cheliform first lateral tooth, and a long, broadened, apparentlypartly prostatic vas deferens in addition to a small discoid alveolar prostate. We therefore surely refer to this specimen as a true D. venustus in our present phylogenetic analysis (fig. 1).

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