Foraminifera: did the first canal systems develop in Involutinida?

Canal systems are advanced architectural features enabling the connection of various body regions via a network of passages. In Foraminifera, they enhance protoplasmic flow. Although they are principally observed in benthic representatives of the multilocular calcitic Order Rotaliida, canal systems presumably first appeared in a tubular, morphologically less complex foraminifer: the Bathonian-Cenomanian trochospiral genus <i>Coscinoconus</i> of the Order Involutinida. Based on the high-resolution analysis of a unique set of aragonitic <i>Coscinoconus</i> specimens, we here demonstrate that the porous system observed in the umbilical mass of these trochospiral Involutinida is a temporary feature. During ontogeny, it is at least partially plugged by aragonite directly secreted by the foraminifer, a process which limits its functional importance. A similar but open (unsealed) porous system is observed in another Involutinida genus, the planispiral Albian marker <i>Hensonina</i>, a controversial form that is here formally reinstated with <i>Hensonina canalicula</i> n. sp. as its type-species. The origin and development of these two porous systems are examined and compared with that of other foraminiferal groups, leading us to propose a clearer definition for wall pores and canal systems. Jurassic-Cretaceous Involutinida offer a fascinating example of a change in the role and function of wall pores through evolution.