Nacella, SCHUMACHER, 1817

González-Wevar, Claudio A., Hüne, Mathias, Rosenfeld, Sebastián, Nakano, Tomoyuki, Saucède, Thomas, Spencer, Hamish & Poulin, Elie, 2019, Systematic revision of Nacella (Patellogastropoda: Nacellidae) based on a complete phylogeny of the genus, with the description of a new species from the southern tip of South America, Zoological Journal of the Linnean Society 186, pp. 303-336 : 307

GENUS NACELLA SCHUMACHER, 1817

Nacella Schumacher, 1817: 179 . Type species (by monotypy) Nacella mytiloides Schumacher, 1817 (= Patella mytilina Helbling, 1779 ).

Patinigera Dall, 1905: 53 . Type species (by original designation) Patella magellanica Gmelin, 1791 . New Synonymy.

Revised diagnosis: The shell is of medium to moderately large size and the thickness varies from hard and robust in some species ( N. magellanica , N. deaurata , N. delesserti , N. terroris , N. concinna and N. clypeater ) to thin and fragile in others ( N. kerguelenensis , N. flammea , N. edgari , N. yaghana sp. nov. and N. mytilina ). The shell morphology is typically elliptical, high-arched, with the apex strongly curved forward and downward, sometimes almost at the anterior end. The surface of the shell varies from very smooth (e.g. N. mytilina ) to strongly radially ridged (e.g. N. magellanica ). The external shell colour is pale-olive to brownish, the apex coppery; the inside is silvery iridescent to reddish bronze.

Remarks: Based on shell morphology, the genus Nacella has traditionally been divided into Nacella s. str. and the subgenus Patinigera ( Powell, 1973) . Members of Nacella s. str. are characterized by a thin and fragile shell, they inhabit seaweeds and are restricted to southern South America ( N. mytilina ) and the Kerguelen Islands ( N. kerguelenensis ), whereas the remaining species were included in Patinigera and exhibit solid shells, are typical inter- and subtidal rocky dwellers, grazers and are broadly distributed in the Southern Ocean. Nevertheless, the distinction between Nacella and Patinigera was not corroborated by molecular analyses; indeed, the respective type species are very closely related ( González-Wevar et al., 2010, 2011a, 2017; this study).

NACELLA YAGHANA GONZÁLEZ- WEVAR & NAKANO