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Fig. 7.4. Stylized drawings of representative genera from subclasses in the Class SPIROTRICHEA . Subclass 
 Stichotrichia : Plagiotoma , Stichotricha, Stylonychia , Urostyla , and Halteria , formerly an oligotrich (compare to 
Strombidium and Laboea ). Note that the bristles of Halteria have been shortened to accommodate the space on the page
the oral primordium in an intracellular tube or neo-
formation organelle (Petz & Foissner, 1992) or on 
the cell surface (Song & Wang, 1996). Oligotrichs , 
such as Cyrtostrombidium , Strombidium , Laboea , 
and Tontonia , demonstrate a considerable diversity 
of somatic ciliary patterns. Agatha (2004a) has pro-
vided a detailed analysis of these patterns and used 
this to justify establishment of several new families 
and genera (see Chapter 17 ). 
 Oral anlagen development is epiapokinetal , that 
is it occurs on the cell surface of the halteriids 
Halteria (Petz & Foissner, 1992; Song, 1993) and 
Meseres (Petz & Foissner, 1992), and these two 
“classical oligotrich” genera undergo a complete 
turn-over or replacement of somatic ciliature 
during division (Agatha, 2004b; Petz & Foissner, 
1992; Song, 1993). Consistently, the “classical 
oligotrich” Halteria falls among the stichotrich 
clade, based on the SSUrRNA gene (Foissner et al., 
2004; Snoeyenbos-West et al., 2002; Strüder-Kypke 
et al., 2002), ITS1 and ITS2 , 5.8S rRNA , and the 
 large subunit rRNA gene (Hewitt et al., 2003), 
 DNA polymerase α (Hoffman & Prescott, 1997), 
and actin (Croft et al., 2003). These morphoge-
netic and molecular features support their affinities 
to the stichotrichs . Agatha (2004b) argued that 
 halteriids are related to strombidiids (= oligotrichs ) 
sensu lato on two main synapomorphies: (1) the 
 enantiotropic division mode; and (2) the de novo
origin of the paroral. We suggest that both these 
features are strongly convergent: the enantiotropic 
division mode is found in a form in the distantly-
related prostome Balanion (Foissner, Oleksiv, & 
Müller, 1990), while many taxa may differentiate 
the paroral de novo . Instead, we would emphasize 
the importance of epiapokinetal stomatogenesis , 
the complete turnover of the somatic ciliature, and the
molecular affinities, all of which relate halteriids 
to the stichotrichs . Thus, the proposed oligotrich 
taxo nomies (e.g., Agatha, 2004b; Laval-Peuto, 
Grain, & Deroux, 1994; Lynn & Small, 1997; Petz 
& Foissner) are refuted: the Family Halteriidae
must be transferred to the Subclass Stichotrichia 
(see Chapter 17 ). Halteriids can be considered 
as stichotrichs , highly adapted to the planktonic 
habitat. We only recognize the Order Strombidiida 
in the Subclass Oligotrichia (see Chapter 17 ). 
 The tintinnids deserve special mention because of 
their long-standing independent status as a group, 
their conspicuousness in the marine plankton, and 
the exceedingly large number of described species, 
well over 1,200. Stomatogenetic (Dale & Lynn, 
1998; Petz & Foissner, 1992) and molecular fea-
tures (Strüder-Kypke et al., 2002; Snoeyenbos-West 
et al., 2002) place them in the Subclass Choreotrichia 
alongside their aloricate relatives. In addition to 
the lorica , they are distinguished by a number of 
peculiar features: tentaculoids , a contractile body, 
a lateral cytoplasmic lobe apparently used in lorica 
construction, short somatic cilia arranged in char-
acteristic patterns dependent upon species, and a 
 perilemma surrounding the entire body and cili-
ature. Doubts have been cast on the taxonomic util-
ity of lorica morphology, both since the description 
by Laval-Peuto (1977) of a Favella species making 
a Coxliella -like lorica and by quantitative analyses 
of lorica variation that conclude it is not feasible 
to objectively distinguish many species based on 
lorica form (Davis, 1981). Despite the recent suc-
cess in automatic categorization by lorica form of 
five species of Cymatocylis by an artificial neural 
network (Culverhouse et al., 1994) and linear 
discriminant analysis (Williams, McCall, Pierce, 
& Turner, 1994), we support Laval-Peuto and 
Brownlee (1986) who recommended a systematic 
approach based on cytology as revealed by pro-
targol staining. Only a handful of species have been 
stained so far, but clear somatic kinetid patterns 
are emerging, such as the presence of longer dor-
sal and ventral kineties that separate left and right 
fields of shorter kineties (e.g., Agatha & Riedel-
Lorjé, 2006; Agatha & Strüder-Kypke, 2007; Choi, 
Coats, Brownlee, & Small, 1992; Foissner & 
Wilbert, 1979; Laval-Peuto & Brownlee, 1986). 
Nevertheless, lorica form has been the major 
diagnostic feature for the only new family of tin-
tinnids established since 1979 (Sniezek, Capriulo, 
Small, & Russo, 1991; Snyder & Brownlee, 1991)! 
Because of the lack of comparative data on kinetid 
patterns , we believe it is premature to redistribute 
 tintinnid genera among families. In the Subclass 
 Choreotrichia , we therefore continue to recognize 
the loricate Order Tintinnida with its classical 
“loricate” families while genera in the aloricate 
Order Choreotrichida are divided into four mono-
typic orders based primarily on variations in 
somatic kinetid patterning (see Chapter 17 ). 
 Finally, researchers continue to explore rela-
tionships within the stichotrichs . The exceedingly 
complex ventral cirral patterns of stichotrichs 
7.1 Taxonomic Structure 149
have lead taxonomists to use features of division 
morphogenesis as a means to resolve relation-
ships among taxa. This approach is premised on 
the conservative nature of developmental pat-
terns as argued by Fauré-Fremiet (1948a) and 
Corliss (1961, 1967, 1968, 1979). There is a rich 
literature using these morphogenetic patterns to 
resolve relationships within the stichotrichs (e.g., 
Berger & Foissner, 1997; Borror, 1979; Borror 
& Hill, 1995; Eigner, 1997, 1999, 2001; Fleury 
et al., 1985a, 1985b, 1986; Martin, 1982; Wicklow, 
1982). Other researchers have primarily used the 
SSUrRNA genes. While the Subclass Stichotrichia 
appears to be monophyletic and now includes the 
 halteriids (see above), it is still quite difficult to rec-
oncile morphological and molecular approaches at 
the family and genus levels, although current molec-
ular evidence at least supports a clade of Stylonychia -
related species (Bernhard et al., 2001; Berger & 
Foissner; Foissner et al., 2004; Hewitt et al., 
2003; Schmidt, Bernhard, Schlegel, & Foissner, 
2007), suggested already in a cladistic analysis of 
morphological traits (Berger & Foissner). We have 
done our best to reconcile these data, but the effort 
is obviously unfinished as there is a considerable 
amount of convergence in morphological traits (see 
Wiackowski, 1988). We have remained conservative 
in our taxonomic treatment of this subclass and rec-
ognize three orders: (1) Order Stichotrichida , includ-
ing genera such as Plagiotoma and Stichotricha , 
whose cirri are arranged, often in many, linear files; 
(2) Order Sporadotrichida , such as Stylonychia , in 
which cirri are distributed “sporadically” in con-
spicuous frontal, ventral, and transverse groupings; 
and (3) Order Urostylida , such as Urostyla , in which 
the frontoventral cirri are arranged in two or more 
zig-zag files on the ventral surface (Fig. 7.4) (see 
Chapter 17 ). 
 In conclusion, we recognize seven subclasses in the 
Class SPIROTRICHEA : (1) Subclass Protocruziidia ; 
(2) Subclass Phacodiniidia ; (3) Subclass Licno-
phoria ; (4) Subclass Hypotrichia ; (5) Subclass 
 Oligotrichia ; (6) Subclass Choreotrichia ; and (7) 
Subclass Stichotrichia . Molecular phylogenetics 
suggests that the taxa are ordered in this manner 
with Protocruzia at the base of the spirotrich 
lineage and various stichotrichs , like Stylonychia
and Sterkiella , at the tip (Bernhard