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features of the somatic cortex (Grain, 1984; Lynn, 1981, 1991) and by recent molecular phylogenetic analyses (Baroin-Tourancheau, Delgado, Perasso, & Adoutte, 1992; Bernhard et al., 2001; Hirt et al., 1995; Shin et al., 2000), which have built on earlier work (Elwood, Olsen, & Sogin, 1985). Spirotrichs appear to have diverged early in the evolution of the Subphylum Intramacronucleata , possibly from a Protocruzia - or Phacodinium -like ancestor, which had multiple adoral polykinetids along the left side of the oral cavity and somatic dikinetids or simple linear somatic polykinetids (Da Silva Neto, 1993a; Didier & Dragesco, 1979; Grolière, de Puytorac, & Detcheva, 1980a). It is thought that polymerization of the adoral polykinetids and their extension over the anterior body surface, accompanied by a reduc- tion in the somatic ciliature, gave rise to the body forms exemplified by the more speciose subclasses in the class, such as the stichotrichs and tintinnid choreotrichs . There is no strong synapomorphy uniting the ciliates assigned to this class, although they repeat- edly form a robust cluster based on SSUrRNA sequences (Bernhard et al., 2001; Hammerschmidt et al., 1996; Shin et al., 2000). Three features typify the group. First, the adoral zone of mem- branelles is a prominent feature of the oral region, typically extending out onto the anterior end in a counter-clockwise spiral. Yet, this is also a feature of members of the Class HETEROTRICHEA (see Chapter 6 ) and of some colpodeans (see Chapter 12 ). Second, macronuclear DNA is replicated in a single replication band that passes from one end of smaller macronuclei to the other end of the nucleus or by two replication bands proceeding from the ends to the middle in more elongate macronuclei (Fig. 7.1) (Raikov, 1982). Nevertheless, members of the Class PHYLLOPHARYNGEA have been reported to have a type of \u201creplication band\u201d although DNA synthesis has not yet been demon- strated in it and its morphological substructure is not similar to that of the spirotrichs (Raikov, 1982). On the other hand, replication bands have not been observed in Protocruzia (Ammermann, 1968; Ruthmann & Hauser, 1974) and Phacodinium (Fernández-Galiano & Calvo, 1992; Da Silva Neto, 1993a), which are both members of the \u201cmolecular spirotrich clade\u201d (Fig. 7.2). Thirdly, somatic cili- ation tends to be reduced in all species but those assumed to represent an ancestral type, which include, as examples, the holotrichously ciliated Protocruzia (Subclass Protocruziidia ), Phacodinium (Subclass Phacodiniidia ), Plagiotoma (Subclass Sticho trichia ), Kiitricha (Subclass Hypotrichia ), and Strombidinopsis (Subclass Choreotrichia ). A molecular or cell biological trait may ultimately be found as a synapomorphy for this clade, but we currently still seek a strong synapomorphy for the class. 7.1 Taxonomic Structure Corliss (1979) placed the spirotrichs as the Subclass Spirotricha in the Class POLYHYMENOPHORA because of their adoral zone of multiple mem- branelles. He recognized four orders within the class: (1) Order Heterotrichida ; (2) Order Odonto- stoma tida ; (3) Order Hypotrichida ; and (4) Order Oligotrichida . We have discussed above (see Chapter 6 ) the reasons for removal of the heterot- richs from this assemblage, based on the structure of the somatic kinetid and its postciliodesma (Lynn, 1981, 1991), the absence of replication bands in the macronuclei, and the use of extramacronuclear microtubules during macronuclear division (Lynn, 1996a). Schrenk and Bardele (1991) compared the somatic kinetid of the odontostomatid Saprodinium to that of the armophorid Metopus . Although the kinetid similarities between these two major groups are not strong, their kinetids differ from those of the hypotrichs , stichotrichs , oligotrichs , Protocruzia , and Phacodinium . We now know that at least one odontostomatid , Epalxella , has affinities at the molecular level with plagiopylids (Stoeck, Foissner, & Lynn, 2007), and so we trans- fer the odontostomatids out of the spirotrichs and place them with the plagiopylids (see Chapter 14 ). Lynn and Strüder-Kypke (2002) have confirmed that Licnophora is a spirotrich , and this genus now establishes the type of a new spirotrich subclass. Fig. 7.1. Replication bands move from one end of the macronucleus (arrow) and are the structures responsible for macronuclear DNA synthesis in spirotrichs . These bands are characteristic of the majority of spirotrichs , such as the hypotrich Euplotes (left) and the oligotrich Strombidium (right). (Redrawn from Salvano, 1975.) 7.1 Taxonomic Structure 143 144 7. Subphylum 2. INTRAMACRONUCLEATA: Class 1. SPIROTRICHEA We have elevated the Orders Oligotrichida and Hypotrichida to Subclass rank, following Lynn and Small (1997) and now recognize seven sub- classes: (1) Subclass Protocruziidia ; (2) Subclass Phacodiniidia ; (3) Subclass Licnophoria : (4) Subclass Hypotrichia ; (5) Subclass Oligotrichia ; Fig. 7.2. Stylized drawings of representative genera from subclasses in the Class SPIROTRICHEA . Subclass Protocruziidia : Protocruzia . Subclass Licnophoria : Licnophora . Subclass Phacodiniidia , Phacodinium . Subclass Hypotrichia : Euplotes ; Diophrys (6) Subclass Choreotrichia ; and (7) Subclass Stichotrichia . Corliss (1979) removed Protocruzia from the Family Spirostomidae and placed it incer- tae sedis in the Suborder Philasterina (Fig. 7.2). Small and Lynn (1985) recognized the Family Protocruziidae Jankowski in Small and Lynn, 1985 and established this as the type family for the Order Protocruziida Jankowski in Small and Lynn, 1985. De Puytorac, Grain, and Mignot (1987) established the Subclass Protocruziidia , which we recognize herein (see Chapter 17 ). As noted above, SSUrRNA gene sequences clearly relate Protocruzia to the spirotrichs , although the levels of statistical support are often not strong (Hammerschmidt et al., 1996; Shin et al., 2000). Should it be recognized as type for a new monotypic class? Corliss (1979) established the Family Phacodini- idae , placing the genera Phacodinium and Transitella in it (Fig. 7.2). As noted above, SSUrRNA gene sequences clearly relate Phacodinium to the spiro- trichs (Bernhard et al., 2001; Shin et al., 2000). Fernández-Galiano and Calvo (1992) noted that Phacodinium can be related to the hypotrichs by the following: its dorsoventral differentiation; some somatic poly kinetids with two rows of kine- tosomes, which they called pseudocirri ; and the polykinetid-like nature of its paroral. Small and Lynn (1985) established the Order Phacodiniida with the type family Phacodiniidae . Following the recommendation of Shin et al. (2000), we elevate the order to subclass rank, attributing authorship to Small and Lynn. As noted above, Corliss (1979) also placed Transitella in the Family Phacodiniidae . However, Iftode, Fryd-Versavel, Wicklow, and Tuffrau (1983) drew attention to the structural differ- ences in the somatic polykinetids, the develop- ment of oral nematodesmata forming a basket-like cytopharyngeal structure, and the presence of a paroral composed of two parallel files of kineto- somes to substantiate their establishment of the Family Transitellidae (Fryd-Versavel & Tuffrau, 1978). However, here we follow Foissner, Adam, and Foissner (1982) who argued that the genus Transitella did not differ substantially from the genus Balantidioides . They placed Transitella as a junior synonym to Balantidioides , and placed the Family Transitellidae as a junior synonym of the Family Reichenowellidae , in which they included Reichenowella and Balantidioides . We place the Family Reichenowellidae incertae sedis in the Subclass Hypotrichia and await molecular evidence