Dendronotusnanus Marcus & Marcus, 1967: 210–214 Farmer, 1980: 72 Robilliard, 1972: 428–430 A synoptic review of the family Dendronotidae (Mollusca: Nudibranchia): a multilevel organismal diversity approach Korshunova, Tatiana Bakken, Torkild GrØtan, Viktor V. Johnson, Kjetil B. Lundin, Kennet Martynov, Alexander Contributions to Zoology 2021 2020-08-28 90 1 93 153 7R2BW Marcus & Marcus, 1967 , Marcus and Marcus 1967 [129,622,925,952] Gastropoda Dendronotidae Dendronotus Animalia Nudibranchia 32 125 Mollusca species nanus      Dendronotusnanus Marcus & Marcus, 1967: 210–214, Figs 64–65;  Farmer, 1980: 72;  Robilliard, 1972: 428–430.   Diagnosis(original description). Body narrow. Six pairs of branched dorsolateral appendages. Circa six oral veil appendages. Fiveappendages (posterior onesthe longest) of rhinophoral stalks. Lateral papilla of rhinophoral sheaths present. Rhinophores with about 15 lamellae. Circa 20 lip papillae. Basal colour semitransparent grayish with a slight reddish hue and a little brown pigment, with white line bordered foot edge, white tipped dorsolateral appendages with blackish brown subapical rings and an orange base. Masticatory processeses with crested pointed denticles. Radula with up to 26 rows of teeth. Central tooth quite narrow, with deep furrows and with up to 10 distinct denticles. Up to 14 lateral teeth commonly smooth, occasionally with up to 12 denticles. Ampulla was not described in the original description. Bursa copulatrix large, rounded to oval. Seminal receptaculum small placed distally at considerable distance from the vaginal opening. Glandular part of prostate was reported in the original description as in early development of differentiation. The vas deferens is extremely long, with numerous loops, penis moderately short, straight, with blunt tip. Body length up to 13 mm.   Distribution. NE Pacific, Baja California, Puerto Peñasco, Sonora, Mexico.   Bathymetry. Floating on seawater surface.   Remarks.  Dendronotus nanuswas considered a synonym of  D. irisby Stout et al. (2010), but in the absence of molecular data we prefer to keepthem separate. Furthermore, despitethe fact that Stout et al. (2010)mentioned only minor morphological differences between  D. irisand  D. nanus, Marcus and Marcus (1967)in their original description specially highlighted that  D. nanusdiffers from  D. irisby a considerably longer vas deferens in animals of only 13 mmlength (an considered to be not fully mature), whereas  D. iristhat was studied anatomically by Robilliard (1970)had a considerablylarger average body length 65–120 mmbut a significantly shorter vas deferens. In the BOLD database there is a sequence of  D. nanus(in GenBank identified as  D. iris), but from a very remote location in British Columbia whereas the typelocality of  D. nanusis Baja California, Sonora, thus this available sequence does not represent a true  D. nanus. Even if taken into account that the glandular part of vas deferens likely is underdeveloped in  D. nanus(see Marcus & Marcus, 1967), the non-glandular muscular part of vas deference of  D. nanusis considerably longer than in  D. iris. Robilliard (1972)compared  D. irisand  D. nanusin detail and mentioned similarity of both species but did not synonymize them. All these characters need to be re-analysed before any further attempts at synonymizing these species should be done.