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forms, such as peritrichs , suctorians , and chonotrichs . Using similarities in division mor- phogenesis and an imagined evolutionary trans- formation from hymenostome to thigmotrich to peritrich, Fauré-Fremiet (1950a) made the case for the \u201c hymenostome \u201d affinities of the peritrichs (Fig. 1.1). His student, Guilcher (1951), argued that suctorians and chonotrichs ought not to be 1.2 The Age of the Infraciliature (1950\u20131970) 3 Fig. 1.1. A Schematic drawings of the hymenostome Tetrahymena, the thigmotrich Boveria, and the peritrich Vorticella. Fauré-Fremiet (1950a) related these three groups in a transformation series, imagining that evolution of the peritrich form proceeded through a thigmotrich-like intermediate from an ancestral Tetrahymena-like hymenos- tome. B Schematic drawings of the cyrtophorine Chilodonella and of the mature form and the bud of the chonotrich Spirochona. Guilcher (1951) argued that the similarities in pattern between the chonotrich bud and the free-living cyrtophorine suggested a much closer phylogenetic relationship between these two groups although the classification scheme of Kahl suggested otherwise (see Table 1.1) 4 1. Introduction and Progress in the Last Half Century greatly separated from other ciliate groups, and she claimed that chonotrichs might in fact be highly derived cyrtophorine gymnostomes (Fig. 1.1). Furgason (1940) in his studies of Tetrahymena had imagined a more global evolutionary transfor- mation of the oral apparatus of ciliates, premissed on the assumption that the three membranelles or oral polykinetids of Tetrahymena and the hymenos- tomes preceded the evolution of the many mem- branelles of the heterotrichs , like Stentor (Fig. 1.2). This view was supported by Fauré-Fremiet (1950a) and Corliss (1956, 1961) who envisioned the hymenostomes as a pivotal group in the evo- lutionary diversification of the phylum. Corliss (1958a) used this concept of transformation of oral structures from simpler to more complex to argue that the hymenostomes , in their turn, had their ancestry in \u201c gymnostome \u201d-like forms, such as the nassophorean Pseudomicrothorax , which itself became another pivotal ancestral type. This led to the rearrangement of higher taxa and the proposal of a \u201cFaurean\u201d classification system by Corliss (1961) (Table 1.2). This new view still maintained the Holotricha and Spirotricha , but the opalinids had now been removed based on the recognition that they shared many significant features with flagellate groups (Corliss, 1955, 1960a). Considering the work of the French ciliatologists, Corliss (1961) transferred the peritrichs , suctorians , and chonotrichs into the Holotricha , recognizing their probable ancestry from groups placed in this subclass. Oral structures continued to play a dominant role in characterizing orders as indicated by the common suffix \u201c-stomatida\u201d (Table 1.2). Of course, the underlying assumption of the transformation of oral structures proposed by Fauré- Fremiet, Furgason, Corliss, and others was that the oral polykinetids or membranelles of these differ- ent ciliates \u2013 Pseudomicrothorax , Tetrahymena , and Stentor \u2013 were homologous. It was the inven- tion of the electron microscope, which was just beginning to demonstrate its applicability during the latter part of this period, that was to provide the evidence to refute this assumption and therefore undercut the general application of this concept. Fig. 1.2. Schematic drawings of three ciliates that have multiple oral polykinetids. The hymenostome Tetrahymena has three oral polykinetids and a paroral while the spirotrich Protocruzia and the heterotrich Stentor have many more than three. Furgason (1940) imagined that evolution proceeded by proliferation of oral polykinetids or membranelles and so the major groups of ciliates could be ordered by this conceptual view into more ancestral-like and more derived 1.3 The Age of Ultrastructure (1970\u20131990) As with other ages, the technological roots of the Age of Ultrastructure began in the 1950s and 1960s. The silver proteinate staining technique of Bodian or protargol staining became established as the light microscopic stain of choice during this period, although it had its technological innova- tors in the previous age (Kozloff, 1946; Kirby, 1950; Tuffrau, 1967). However, it was electron microscopy, promoted by Pitelka (1969), that gained preference in resolving questions in both the systematics and cell biology of ciliates. These early results, coupled with two seminal papers by 1.3 The Age of Ultrastructure (1970\u20131990) 5 Table 1.2. Faurean classification and post-Faurean system adopted by Corliss (1979).a Faurean Era (1950\u20131970) Post-Faurean Era (1970\u20131981) Subphylum Ciliophora Phylum Ciliophora CILIATA KINETOFRAGMINOPHORA OLIGOHYMENOPHORA Holotricha Gymnostomata Hymenostomata Gymnostomatida Primociliatida Hymenostomatida Rhabdophorina Karyorelictida Tetrahymenina Cyrtophorina Prostomatida Ophryoglenina Suctorida Archistomatina Peniculina Chonotrichida Prostomatina Scuticociliatida Trichostomatida Prorodontina Philasterina Hymenostomatida Haptorida Pleuronematina Tetrahymenina Pleurostomatida Thigmotrichina Peniculina Vestibulifera Astomatida Pleuronematina Trichostomatida Peritricha Astomatida Trichostomatina Peritrichida Apostomatida Blepharocorythina Sessilina Thigmotrichida Entodiniomorphida Mobilina Arhynchodina Colpodida POLYHYMENOPHORA Rhynchodina Hypostomata Spirotricha Peritrichida Synhymeniida Heterotrichida Sessilina Nassulida Heterotrichina Mobilina Nassulina Clevelandellina Spirotricha Microthoracina Armophorina Heterotrichida Cyrtophorida Coliphorina Heterotrichina Chlamydodontina Plagiotomina Licnophorina Dysteriina Licnophorina Oligotrichida Hypocomatina Odontostomatida Tintinnida Chonotrichida Oligotrichida Entodiniomorphida Exogemmina Oligotrichina Odontostomatida Cryptogemmina Tintinnina Hypotrichida Rhynchodida Hypotrichida Stichotrichina Apostomatida Stichotrichina Sporadotrichina Apostomatina Sporadotrichina Astomatophorina Pilisuctorina Suctoria Suctorida Exogenina Endogenina Evaginogenina a Classes are indicated in bold capital letters; subclasses, in italics; orders, in bold with the ending \u201c\u2212ida\u201d; suborders, further indented with the ending \u201c\u2212ina\u201d. 6 1. Introduction and Progress in the Last Half Century Jankowski (1967a, 1973c), prompted the French group of de Puytorac, Batisse, Bohatier, Corliss, Deroux, Didier, et al. (1974b) and, both with his French colleagues and independently, Corliss (1974a, 1974b) to propose revised classifications. Corliss (1979) used a slightly modified version in his third edition to \u201cThe Ciliated Protozoa\u201d (Table 1.2). About this time, Jankowski (1980) proposed a new system, which still placed major emphasis on oral features as indicated by the names of some of his classes \u2013 Apicostomata , Pleurostomata , Rimostomata , Synciliostomata , Cyrtostomata , and Hymenostomata . The major feature of these post-Faurean schemes was the prominent elevation of oral features. The three classes in the phylum were now character- ized by the nature of the oral apparatus: small, simple kinetal fragments characterized the Class Kinetofragminophora ; typically three oral poly- kinetids or membranelles characterized the Class Oligohymenophora ; and many more than three mem- branelles characterized the Class Polyhymenophora (Table 1.2). All three names derived from the conceptual vision of Jankowski (1967a, 1973c, 1975), which shared the same assumption as Furgason\u2019s: homology was assumed among \u201coligo\u201d- membranelles and \u201cpoly\u201d-membranelles. Before we return to a refutation of this assump- tion, it is