Composition and ontogeny ofDictyoconites (aulacocerida,cephalopoda)

Dictyoconites from the middle Triassic Cassian Formation is a characteristic representative of the Aulacocerida. Embryonic development and construction of the phragmocone is like that of Jurassic belemnites. The siphuncular tube is double-walled with a long retrochoanitic mineralized septal neck continuing into an organic tube. The extended decoupling zone resembles that ofSpirula. Characteristic ofDictyoconites are the tubular »living chamber« and two layered deposits of the muscular mantle on the phragmocone. The Triassic coleoid was a slender squid with visceral mass and mantle cavity encapsuled in shell and the whole conch covered by muscular mantle extending in two lateral apical fins attached to the aragonitic rostrum.