Historical museum specimens
A total of 117 specimens of the Dendronotus robustus species complex (Table 1) from the Gothenburg Natural History Museum (GNM), the Swedish Museum of Natural History, and the Oslo Natural History Museum (NHM-UIO) were investigated, including a study of both external and internal features. The majority of the specimens had been examined and determined as Dendronotus robustus by the nudibranch specialist Nils Odhner between the 1910s to the 1930s. Five of the specimens from the Gothenburg Natural History Museum were sent as loan to the Zoological Museum in Moscow for morphological investigation. Two specimens (GNM 3026 and 3027) were dissected and SEM-studies of their radula were performed (Figure 1, Table 1). Additionally, AM checked all previously identified as D. robustus specimens while he visited GNM in August 2017.
Table 1. Historical specimens of Dendronotus velifer G.O. Sars, 1878 from Swedish and Norwegian museums.