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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 “replication band” 
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 “molecular 
spirotrich clade” (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
 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