Resumen de Gibbula saeniensis dal Pliocene toscano.: (Gastropoda: Trochidae)
- italiano
Viene descritta Gibbula saeniensis n. sp. da depositi infralitorali di sabbie-argillose grigie o sabbie gialle del Pliocene medio-inferiore senese.
- English
The Authors describe Gibbula saeniensis n. sp. from infralittoral grey silty-sand bed outcropping at "Podere Melograni" (S. Gimignano, Siena, Italy). The outcrop is attributed to middle-lower Pliocene. The new species has been found in some other nearby deposits: Pietrafitta, Terre Rosse, Castel S. Gimignano and Bibbiano. These deposits are grey silty-sand or yellow sand, their age ranges between middle-lower Pliocene and middle Pliocene. Gibbula saeniensis is not rare in this area but as far as we know its distribution is restricted to this area of Tuscan. Gibbula saeniensis is characterised by the large size (max. height about 23 mm) and the strong spiral ribs, separated by deep interspaces, covering the whorls and the base. There are six spiral ribs on the last whorl and about seven on the base. Sometime the spiral ribs have a central or subcentral longitudinal superficial sulcus. This species was possibly found by Pantanelli that listed (Pantanelli, 1880) for “Poggio della Staffa” (a locality near Pietrafitta) a Trochus succinctus Monterosato, 1880, that is a recent species, considered a form of Gibbula ardens (von Salis, 1793) showing some similitaries with G.saeniensis, but it is mach smaller, with light and thin spiral ribs. Authors suppose that G. saeniensis might be a descendant of the Miocenic Trochus quadristriatus Dubois, 1831, survived up to middle Pliocene this restricted area. Another endemism of this area seems to be Chiton saeniensis Laghi, 1984.
