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completely, also similar to many stichotrichs , from primordia that develop beside or in between the parental infraciliature (Fig. 7.8) (Song, 1993; Petz & Foissner, 1992). Finally, brief mention should be made of division morphogenesis in the Family Reichenowellidae . This has been described for Balantidioides (= Transitella ?) (Iftode et al., 1983) and character- ized as pleurotelokinetal by Foissner (1996b) since the oral primordium arises by kinetosomal replica- tion in several right lateral kineties. Replication in somatic kineties apparently occurs throughout the length of the kineties and without replacement of the parental kinetids. These features are more akin to the heterotrichs and some colpodeans (Foissner, 1996b; Iftode et al., 1983), thus justifying our cur- rent placement of this family as incertae sedis in the Subclass Hypotrichia . Hypotrichs and stichotrichs have been model organisms for developmental biologists who are interested in probing the underlying mechanisms of pattern formation (e.g., see Frankel, 1989, 1991; Nanney, 1980). The pattern formed in each spe- cies is undoubtedly under genic control, as has been demonstrated for the ventral ciliature of both groups (Génermont et al., 1992; Jerka-Dziadosz & Czupryn, 1995; Jerka-Dziadosz & Dubielecka, 1985) and for the dorsal ciliature of hypotrichs (Heckmann & Frankel, 1968). These genetic traits in patterns of the infraciliature can be conserved across groups of species, as has been carefully demonstrated for Euplotes species (Gates, 1977, 1978b, 1988; Machelon & Génermont, 1984), suggesting that the positional information systems determining pattern can be conserved while other genetic traits, such as enzyme polymorphisms evolve. Nevertheless, there can be considerable phenotypic variation in the numbers of cirri on the ventral surface of hypotrichs (Walker & Grim, 1973). As occurs in the heterotrichs , this varia- tion can be related to the cell size : smaller cells have proportionately fewer oral polykinetids in the adoral zone (Jerka-Dziadosz, 1976) and propor- tionately fewer kinetosomes in each polykinetid (Bakowska & Jerka-Dziadosz, 1980). These are clearly issues that practising taxonomists need to consider as they decide whether to establish a new morphospecies based on quantitative differences in cirral patterns. Qualitative differences occurring within hypotrich species further confound the tax- onomist\u2019s job: Génermont et al. (1992) reported on a mutant of Euplotes that had disturbed positioning of the ventral cirral pattern compared to that of the wild type! In a now classical series of papers on the ultrastructure of morphogenesis in spirotrichs , Jerka-Dziadosz (1980, 1981a, 1981b, 1982) pro- vided not only a model for future studies but also revealed the basic details of the assembly of the somatic and oral infraciliature during the division morphogenesis of the stichotrich Paraurostyla (Fig. 7.9). The model described below is consistent with the light microscopic observations on the division morphogenesis within the spirotrich subclasses. Specifically, the anarchically arranged dikinetids on the left side of the oral primordium are assembled into rows of dikinetids, and subsequent kinetosomal replication adjacent to the anterior kinetosome of each dikinetid adds additional kinetosomal rows (Fig. 7.9a) (Jerka-Dziadosz, 1981a). Dikinetids on the right side of the oral primordium rotate so that the dikinetid axis is transverse to the cell anterior- posterior axis, forming an anterior-posterior file of kinetosomes as the primordium for the paroral structures, the paroral and endoral \u201cmembranes\u201d develop (Fig. 7.9b) (Jerka-Dziadosz, 1981b). Within the somatic ventral streak primordia, dikinetids align in an anterior-posterior file. Subsequently, these become partitioned in groups by intrastreak microtubules while kinetosomal replication at the structurally \u201canterior\u201d end of each dikinetid adds kinetosomes to complete cirral development (Fig. 7.9c) (Jerka-Dziadosz, 1980). Fleury, Le Guyader, Iftode, Laurent, and Bornens (1993) demonstrated using immunocytochemistry that a protein scaf- 7.5 Division and Morphogenesis 167 168 7. Subphylum 2. INTRAMACRONUCLEATA: Class 1. SPIROTRICHEA Fig. 7.9. Schematic of the development of cortical structures in the stichotrich Paraurostyla weissei . ( a ) Development on the left side of the oral primordium field showing the sequential formation of five oral polykinetids by assembly of kinetosomes and dikinetids in the anarchic region . (from Jerka-Dziadosz, 1981a.) ( b ) Development on the right side of the oral primordium field showing the alignment and then dissociation of dikinetids to form the endoral and paroral structures. (from Jerka-Dziadosz, 1981b.) ( c ) Development of the somatic polykinetids in the marginal cirral files from a linear file of kinetids (bottom) to separate hexagonally-packed polykinetids (top), separated during the process by groups of intrastreak micro tubules (oblique lines). (from Jerka-Dziadosz, 1980.) fold appears transiently and cirral kinetosomes are distributed along this. Replication and devel- opment of dorsal dikinetids begins similarly to that in ventral streaks, but differences exist in the fibrillar associates, kinetosomal connectives, and the ultimate arrest of development at the dikinetid stage (Jerka-Dziadosz, 1982). This is similar to the pattern already described by Grimes and Adler (1976) and markedly different from that of Euplotes (Ruffolo, 1976b). Following cell division , there are relatively few species that elaborate extracellular structures: the loricae of tintinnids and the tubes of Stichotricha being exceptional. In tintinnids , it is the proter that constructs the new lorica while the opisthe is left with the old one (Laval-Peuto, 1994). Typically, construction of the protolorica takes only a few minutes following division and is constructed from the posterior to the anterior. Lorica construction involves the somatic cilia, which manipulate the secreted contents of the formative vesicles. Lorica length can be quite variable while lorica diameter is less so. If the tintinnid becomes separated from the protolorica , it may secrete a new lorica, called the paralorica . The paralorica can appear quite dif- ferent, possibly due to its formation, which takes place over several hours, much more slowly than the few minutes taken for protolorica construction (Laval-Peuto, 1994). 7.6 Nuclei, Sexuality and Life Cycle There is a tremendous diversity in macronuclear shapes among the spirotrichs . Generally, macro- nuclei are globular to ellipsoid and often in pairs, which are joined together by a membranous isthmus that may only be visible by electron microscopy (e.g., Walker & Goode, 1976). In some instances, there can be dozens of smaller macronuclei (e.g., Urostyla , Fig. 7.4) while in other instances, the macronucleus may be an elongate \u201cC-\u201d or \u201cE- \u201dshape as in the hypotrichs where macronuclear shape may even be diagnostic of a species (Fig. 7.2) (Curds, 1975a; Tuffrau, 1960). Micronuclei can be globular to ellipsoid and range from one to many more than ten. A characteristic feature of the macronuclear cycle of spirotrichs is the emergence during the time of cell division of a replication band , formerly called a reorganization band (Fig. 7.1). Stein (1859) was probably the first to observe these in Euplotes , whose replication bands have been the subject of cell biological studies (Bonifaz & Plaut, 1974; Gall, 1959; Olins & Olins, 1994; Olins et al., 1988). Replication bands in Euplotes begin at each end of the elongate macronucleus and proceed towards the middle. The bands themselves are composed of a forward zone in which the chromatin is decondensed