Revision of the genera Parviturbo and Pseudorbis (Gastropoda, Skeneidae)

A revision of the genus Parviturbo Pilsbry & McGinty, 1945, distributed in the Atlantic Ocean, the American Pacific, and the Tropical South Pacific, is presented for the first time. In total 33 species were studied, of which 12 were already known (5 in the Eastern Atlantic, 5 in the Western Atlantic, and 2 in the American Pacific); 20 more are described as new species (4 in the Eastern Atlantic, 12 in the Western Atlantic, and 4 in the Tropical South Pacific) and one more from the Mediterranean is presented without a name. We provide new data on the radula for Parviturbo insularis, and the morphology of the shell is described and illustrated for all the species using scanning electron microscopy. Data on their distribution and habitat are also provided, and their generic allocation is discussed. The presence of species Parviturbo in the Tropical Pacific is confirmed. The type material of several species (Parviturbo rehderi Pilsbry & McGinty, 1945, Cyclostrema granulum Dall, 1899 and Delphinula tuberculosa d’Orbigny, 1842 is illustrated and a lectotype is designated for the latter species. Parviturbo dibellai Buzzurro & Cecalupo, 2007 is excluded from the genus, and considered a junior synonym of Fossarus eutorniscus Melvill, 1918; the species is transferred to Vitrinellinae but without a definite generic assignment. The two known Recent species of Pseudorbis, a genus close to Parviturbo, are studied for comparison and the differences and similarities between these two genera are discussed.