ABSTRACT
In most molecular and morphological studies of flatworms, the Macrostomorpha are interpreted as the plesiomorphic sister group to all higher rhabditophoran platyhelminth taxa (Tyler 2001, this volume; Littlewood and Olson 2001, this volume). The taxon was established by Doe (1986a) to encompass the Haplopharyngida and the Macrostomida sensu Karling (1974). Doe used three synapomorphies to characterize this group: the duo-gland adhesive organs (Tyler 1976, 1977); the pharynx simplex coronatus (Doe 1981); and the aciliary spermatozoa (Ehlers 1984). The Macrostomorpha are therefore a very well-defined monophyletic group in the lower platyhelminths.
