Révision de Cibaster bourgeoisanus (d'Orbigny, 1853) et de la position du genre Cibaster Pomel, 1883 au sein des Holasteroida

The genus Cibaster Pomel, 1883, with its type species Cibaster bourgeoisanus (d'Orbigny, 1853), has poorly diagnostic characters. So, authors comprise this genus as Cardiaster Forbes, 1850, or as Offaster Desor, 1858. The study of numerous specimens of Cibaster bourgeoisanus, from the Coniacian of the “Craie de Villedieu” in the stratotypical region, demonstrates that this species is paedomorphic compared to Cardiaster, with juvenile pore-pairs and a shallow frontal groove. The plastron structure is derived from the pattern found in Pseudholaster Pomel, 1883. A close relationship between Pseudholaster and Cibaster is probable, with Protocardiaster Smith and Wright, 2003 as intermediate. Cibaster is clearly distinct from Offaster, because this last genus have a meridosternal plastron.