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Oldest representatives of the superfamily Cirroidea (Vetigastropoda) with notes on early phylogeny

Two new genera, Barrandecirrus (Porcelliinae) and Pernericirrus (Agnesiinae), from Upper Silurian marine sediments of the Prague Basin (Barrandian area, central Bohemia) are described. Both these genera belong to the family Porcelliidae and represent the oldest representatives of the superfamily Cirroidea (Vetigastropoda). The sinistrally coiled teleoconch of Barrandecirrus filiformis (Perner) suggests that the pseudobilaterally symmetrical teleoconch of the younger genera of Porcelliinae (Porcellia and Coloniacirrus) is a secondary shell character that originated during post-Silurian evolution of this group. In addition, the sinistral, low trochospiral teleoconch of early Agnesiinae [Pernericirrus sinistorsus (Perner) and Agnesia costata (Goldfuss)] as well as the asymmetrical position of the selenizone and the sinistral teleoconch in early Porcelliinae (Barrandecirrus filiformis) support the opinion that both Porcelliinae and Agnesiinae arose from the same stock. Data presented also suggest that the superfamily Cirroidea evolved during the Silurian or earlier, and it has developed parallel to and independently of other larger groups of the Vetigastropoda such as the Pleurotomarioidea and the Trochoidea.