The adult shell (teleoconch) of the enigmatic tubular Givetian fossil Trypanopora is comprised of two principal layers: an outer fibrous prismatic layer and an inner micro-lamellar (irregular cross-bladed) layer, with local, closely-spaced disruptive punctation. The fine preservation suggests an original calcite composition. The shell microstructure shows great similarities with that of both vermiform ‘gastropods’ and tentaculitoids, suggesting a close affinity between Trypanopora and these groups. The septa have an irregular micro-lamellar (cross-bladed) microstructure in continuity with the inner wall, and a morphology unlike that of any known mollusc. The class Tentaculitoidea is emended to include two new orders: Microconchida for the vermiform ‘gastropods’ and Trypanoporida for Trypanopora and allied genera. □Trypanopora, microstructure, protoconch, teleoconch, fibrous prismatic layer, micro-lamellar layer, tubulation, septation, vermiform ‘gastropods’, Tentaculitoidea, Microconchida, Trypanoporida.