Nacella SCHUMACHER 1817

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