A long-lasting debate is held about the how and why of gastropod torsion. The term describes a phylogenetic and ontogenetic 180° rotation of the visceral sac and contained organs relative to head and foot region. Effects of this rotation are said to be a gut bent to open up anteriorly, gills (ctenidia) that lie in an anterior mantle cavity and nerve cords between the pleural and visceral ganglia that are arranged in a crossing, figure-of-eight-like form, while one connection traverses above and one below the intestinal tract. This is called streptoneury. By arresting torsion during ontogeny we are able to analyse the formation, arrangement and position of organs such as gut, mantle, shell and the nervous system. A particular focus is on the role of torsion for streptoneury, challenging century-old ideas about relationships.
Turning snails into slugs