Flashback and foreshadowing—a review of the taxon Opisthobranchia

Opisthobranchia have experienced an unsettled taxonomic history. At the moment their taxonomy is in state of dramatic flux as recent phylogenetic studies have revealed traditional Opisthobranchia to be paraphyletic or even polyphyletic, allocating some traditional opisthobranch taxa to other groups of Heterobranchia, e.g. Pulmonata. Here we review the history of Opisthobranchia and their subgroups, explain their traditionally proposed...