Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota)

An overview of the controversial proposal for the major eukaryote taxon 'Excavata' is presented. Excavata is predicted to include at least ten distinct groups: jakobids, Malawimonas, Trimastix, Carpediemonas, retortamonads, diplomonads, Heterolobosea, oxymonads, parabasalids and Euglenozoa. These 'excavates' have broadly similar flagellar apparatus organizations, for which a 'universal' terminology is provided. Most, but not all, of these organisms share a distinctive suspension-feeding groove, as well as some or all of a set of seven other proposed cytoskeletal apomorphies. Cladistic analyses of morphological data do not resolve high-level relationships within Excavata. Excavate-rich molecular phylogenies recover some robust clades, but do not support or strongly refute the monophyly of Excavata. A partial classification for excavates is presented, with phylogenetic diagnoses for Excavata and for two novel taxon names, Fornicata (Carpediemonas, retortamonads, diplomonads) and Preaxostyla (Trimastix, oxymonads).