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and somatic kinetids with postcilio-
desmata (Fig. 4.7) in which the postciliary micro-
tubular ribbons are separated by only a single 
microtubule (see Chapter 6 ). Oral structures in 
the karyorelicteans are quite variable, ranging 
from prostomial with simple circumoral ciliature 
to ventrostomial with developed paroral and adoral 
 ciliature . Heterotricheans , like Stentor , are virtually 
all bearers of a paroral and an elaborately developed 
adoral zone of polykinetids (Figs. 4.3, 4.4). 
 The Subphylum Intramacronucleata includes 
the remaining nine classes, each of which will 
Fig. 4.3. Stylized drawings of genera representative of each class in the Phylum Ciliophora: Loxodes – Class 
 KARYORELICTEA ; Stentor – Class HETEROTRICHEA ; Protocruzia , Euplotes – Class SPIROTRICHEA ; Metopus
– Class ARMOPHOREA ; Didinium – Class LITOSTOMATEA ; Chilodonella – Class PHYLLOPHARYNGEA ;
Obertrumia – Class NASSOPHOREA ; Colpoda – Class COLPODEA ; Plagiopyla – Class PLAGIOPYLEA ; 
Holophrya – Class PROSTOMATEA ; and Tetrahymena – Class OLIGOHYMENOPHOREA 
4.1 Taxonomic Structure 95
96 4. Phylum CILIOPHORA – Conjugating, Ciliated Protists with Nuclear Dualism
Fig. 4.4. Scanning electron micrographs of ciliate diversity. A–C Class HETEROTRICHEA . Blepharisma ( A ), Fabrea
( B ), and Stentor ( C ). D–I Class SPIROTRICHEA . The oligotrich Strombidium ( D ), the tintinnids Dictyocysta ( E ) and 
Tintinnopsis ( F ), the stichotrich Stylonychia ( G ), and the hypotrichs Euplotes ( H ) and Uronychia ( I). (Micrographs 
courtesy of E. B. Small and M. Schlegel.)
be briefly characterized here (Table 4.1). Lynn 
(2004) has noted that four of the classes – the 
strongly supported by both molecular and 
morpholo gical characteristics. The remaining five 
 OLIGOHYMENOPHOREA – have less strong 
support from molecules and morphology. Two 
of these latter five, the ARMOPHOREA and 
 PLAGIOPYLEA , are only supported by molecules,
and hence called “riboclasses” (Lynn, 2004). 
 Spirotricheans , like Protocruzia , Euplotes , 
Strombidium , Dictyocysta , Tintinnopsis , Stylonychia , 
and Uronychia (Figs. 4.3, 4.4, Table 4.1), are a 
diverse group, typically having a paroral and 
a well-developed adoral zone of polykinetids . 
The class is rarely strongly supported as a clade by 
molecular phylogenetics. Most of the taxa exhibit 
somatic dikinetids with a poorly developed kineto-
desmal fibril (Fig. 4.7) and two of the included 
subclasses, the Hypotrichia and Stichotrichia , have 
compound ciliary organellar complexes called cirri 
(Figs. 4.3, 4.4, 4.7). The strongest morphological 
synapomorphy for the class is the replication band 
that occurs during macronuclear DNA S-phase 
(see Chapter 7 ). The replication band has been 
confirmed in members of all subclasses except 
the two monotypic Subclasses Protocruziidia and 
 Phacodiniidia . The phacodiniids are undoubtedly 
 spirotrichs by their placement well within the 
spirotrichean clade using the small subunit rRNA 
( SSUrRNA ) molecule (Shin et al., 2000). The situ-
ation for Protocruzia , also the only member of its 
subclass, is more uncertain as it is typically placed 
as the basal lineage in the spirotrich branch. We 
have placed protocruziids in this class because they 
are tenuously associated with it by SSUrRNA gene 
sequences (see Chapter 16 ). However, they may 
warrant separate class status in the future because 
their histone sequences are divergent from other 
spirotrichs (Bernhard & Schlegel, 1998), and they 
exhibit a unique mode of macronuclear division 
(Ammermann, 1968; Ruthmann & Hauser, 1974). 
 Armophoreans , like the armophorid Metopus
and the related clevelandellid Nyctotherus (Figs. 
4.3, 4.5, Table 4.1), are strongly supported only 
by SSUrRNA gene sequences (van Hoek et al., 
2000b). The somatic kinetids of the two subclasses 
within this class are quite different (Fig. 4.7; and see 
 Chapter 8 ). However, Villeneuve-Brachon (1940) 
speculated that these ciliates might be related to 
each other, a view later endorsed by Jankowski 
(1968b) and Albaret (1975). Both free-living and 
endosymbiotic armophoreans are found in anoxic or 
close to anoxic environments and all are presumed 
to have hydrogenosomes . Future research on armo-
phorean hydrogenosomes may reveal synapomor-
phies in their anaerobic metabolism that may more 
strongly confirm this class. 
 Litostomateans , like the haptorians Didinium
and Dileptus and the trichostomes Isotricha , 
Entodinium , and Ophryoscolex (Figs. 4.3, 4.5, Table
4.1) are strongly supported by both SSUrRNA 
gene sequences and by features of the somatic 
kinetid , which is a monokinetid with two trans-
verse ribbons (Fig. 4.7; and see Chapter 9 ). The 
two included subclasses may not be mono phyletic: 
it now appears the haptorians may be a para-
phyletic group (Strüder-Kypke, Wright, Foissner, 
Chatzinotas, & Lynn, 2006). 
 Phyllopharyngeans , like the cyrtophorians 
Chilodonella and Trithigmostoma and the suctorian
Podophrya (Figs. 4.3, 4.6, Table 4.1), form a diverse 
group, strongly supported by both SSUrRNA gene 
sequences and by features of the somatic kinetid , 
which is a somatic monokinetid that has a laterally-
directed kinetodesmal fibril and whose kineto-
somes are underlain by subkinetal micro tubules 
(Fig. 4.7; and see Chapter 10 ). A significant 
feature of the phyllopharyngean oral apparatus is a 
set of radial ribbons of microtubules that support the 
cytopharynx, the phyllae . 
 Nassophoreans , like Obertrumia (Fig. 4.3, Table 
4.1), are also strongly supported by both SSUrRNA 
gene sequences and by features of the somatic 
kinetids, which are monokinetids that can be 
linked as dikinetids by filaments near the base of 
the transverse microtubular ribbon (Fig. 4.7; and 
see Chapter 11 ). In addition, the cytopharyngeal 
basket or nasse of these ciliates exhibits a suite of 
characters not found together in any other class. 
 Colpodeans , like Colpoda (Figs. 4.3, 4.5, 
Table 4.1), are typically well supported by both 
SSUrRNA gene sequences and by features of the 
somatic kinetids, which are dikinetids whose pos-
terior kinetosomes have well-developed transverse 
microtubular ribbons extending posteriorly along 
the kinety, forming the transversodesma or LKm 
fibre (Fig. 4.7; and see Chapter 12 ). 
 Prostomateans , like Holophrya and Coleps (Figs. 
4.3, 4.5, Table 4.1), are not strongly supported by 
molecular signals, but this may in part be due to the 
low taxon sampling for this group. Their somatic 
kinetids show similarities to those of the next three 
classes (Fig. 4.7), and it is only in the details of 
their oral structures and stomatogenesis that the 
group may be distinguished (see Chapter 13 ). 
 Plagiopyleans , like Plagiopyla (Fig. 4.3, Table 
4.1), are strongly supported by SSUrRNA gene 
sequences even though the taxon sampling is low. 
Nevertheless, this is the second “ riboclass ” within 
the phylum because there is no strong synapo-
morphy for the group. The somatic kinetids are 
similar to those of the Classes PROSTOMATEA 
and OLIGOHYMENOPHOREA , showing a well-
developed anteriorly-directed kinetodesmal fibril 
and a radially-oriented transverse microtubular 
ribbon (Fig. 4.7). A remarkable recent discovery 
4.1 Taxonomic Structure 97
98 4. Phylum CILIOPHORA – Conjugating, Ciliated Protists with Nuclear Dualism
is the indication that odontostomatids , represented 
by Epalxella , may form a third clade within 
this class (Stoeck, Foissner, & Lynn, 2007) (see 
Chapter 14 ). 
 Oligohymenophoreans , like the peniculines 
Paramecium and Lembadion , the hymenostomes 
Tetrahymena and Glaucoma , and the peritrichs