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The Prototeuthidina is a well-known group of gladius-bearing coleoids that probably appeared at the end of the Triassic period and disappeared during the latest Cretaceous. Its gladius and hence its mantle is very slender when compared with the other two subgroups. The prototeuthidid gladius is furthermore characterized by a ventrally close (funnel-like) conus.
Figure: Plesioteuthis prisca, Tithonian (late Jurassic), Solnhofen area (Germany). A) specimen in dorsal view preserved with gladius, mantle and fins, B) reconstruction of the gladius, C) imprints of an arm crown consisting of 8 arms, D) star-like arm imprints produced when the dead animal landed on the sea floor in an oral-end-down position. © Dirk Fuchs
Particularly late Jurassic Plesioteuthis prisca is in the focus of debates as its gladius superficially resembles an ommastrephid gladius. Since Plesioteuthis prisca and other prototeuthidids such as late Jurassic Senefelderiteuthis tricarinata or late Cretaceous Dorateuthis syriaca never show more than eight arms, Fuchs (2006a, b) and Fuchs et al. (2007b) regarded the Prototeuthidina as an extinct side branch of early Octopodiformes.
Figure: Head and arm crown of Dorateuthis syriaca from the Cenomanian (late Cretaceous) of Hakel (Lebanon). © Dirk Fuchs