Revision of genus Sabrinella (Gastropoda) and a new minute vetigastropod from the Late Triassic Cassian Formation (N Italy)

A tiny (less than 2 mm adult size) trochiform vetigastropod from the Late Triassic Cassian Formation was misidentified as Delphinula doris LAUBE, 1869, type species of the genus Sabrinella BANDEL, 1993. The holotype of Delphinula doris LAUBE, 1869 (also from the Cassian Formation) is studied and illustrated. This species is fixed as type species of Sabrinella. The other species is described as Geigerella minuta n. gen., n. sp. It is characterized by its small size and by its widened circular aperture that is thickened forming a plate-like continuous peristome. It has a vetigastropod-type protoconch and a non-nacreous acicular shell microstructure. The new genus is tentatively placed in the family Sabrinellidae. Besides Sabrinella and Geigerella, the Late Triassic genera Chilocyclus and Microcheilus as well as the Jurassic Fischeriella are also placed in Sabrinellidae based on the presence of similar widened apertures. Despite the lack of nacre, Geigerella n. gen. could also be related to the families Eucyclidae or Eucycloscalidae. Nacre was commonly lost in small-sized members of otherwise nacreous vetigastropod groups.