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RNA genes . Gene sequence 
data now affirm the affinities of cyrtophorians and 
 chonotrichs (Snoeyenbos-West et al., 2004). We 
now need gene sequence data to complete testing 
the hypothesis of Grell and Meister (1982a) that 
the four groups divide into two major clades: (1) the 
 cyrtophorians and chonotrichs with heteromerous 
macronuclei ; and (2) the rhynchodians and suctorians
with tentacle -like oral structures and toxic extru-
somes. We currently recognize these four groups 
as subclasses. 
 The Subclass Cyrtophoria includes typically 
free-swimming forms, often dorsoventrally flat-
tened with somatic ciliature restricted to the 
ventral surface. The oral ciliature is composed typ-
ically of three kinetofragments, a preoral and two 
 circumoral kineties , which are moved into position 
during stomatogenesis by a complex counter-
clockwise rotation during division morphogenesis 
(see Division and Morphogenesis below). We 
have reverted to the older taxonomic name for 
this group because of its familiarity to many and 
here suppress the subclass name Phyllopharyngia . 
We recognize two orders within the subclass. The 
Order Chlamydodontida includes dorsoventrally-
flattened forms with ventral thigmotactic cilia-
ture and no adhesive organelle or podite (Fig. 
10.1). “Classical” families included in this order 
are the Chilodonellidae , Chlamydodontidae , 
 Gastronautidae , and Lynchellidae . Added to these 
four “classical” families are the monotypic Family 
 Chitonellidae including an unusual loricate genus 
(Small & Lynn, 1981) and the monotypic Family 
 Kryoprorodontidae , which includes the former 
 enchelyid Gymnozoum , an unusual planktonic 
 cyrtophorian (Alekperov & Mamajeva, 1992; Petz, 
Song, & Wilbert, 1995). The second order, Order 
 Dysteriida , includes typically laterally compressed 
forms although the body morphology and oral 
structures can be quite bizarre in this group. 
Instead of thigmotactic ciliature , dysteriids typi-
cally use a posterior podite for attachment to the 
substrate (Fig. 10.1). Substrates may range from 
the substrate of marine and freshwater habitats 
for genera such as Plesiotrichopus and Dysteria
(Deroux, 1976a) to the nasal passages of whales 
and dolphins for Kyaroikeus (Sniezek, Coats, & 
Small, 1995). We place four families in the order: 
 Dysteriidae , Hartmannulidae , Plesiotrichopidae , 
and the newest addition, the Kyaroikeidae . Fauré-
Fremiet (1965) provided one of the first modern 
analyses of dysteriid morphology. This was fol-
lowed by the seminal works of Deroux and his 
collaborators, who have essentially set the mod-
ern groundwork for this subclass (Deroux, 1965, 
1970, 1976a, 1976b, 1977; Deroux & Dragesco, 
1968). Deroux (1994a) has revised the taxonomy 
of the group, introducing new orders, several 
Fig. 10.1. Stylized drawings of representatives of the Subclass Cyrtophoria of the Class PHYLLOPHARYNGEA .
The chlamydodontid Chilodonella . The dysteriids Trochilia and Dysteria . Note that the left side of Dysteria has not 
been drawn so that the somatic ciliation in the ventral groove can be revealed
10.1 Taxonomic Structure 211
new suborders, and several new families. He also 
reviewed the tremendous amount of morpho-
logical diversity within the dysteriids , suggest-
ing several phylogenetic trends that bear testing 
by gene sequence data. We have followed Lynn 
and Small (2002), remaining conservative until 
molecular evidence can corroborate these further 
subdivisions proposed by Deroux (1994a) and 
others. Li and Song (2006b) have added the dys-
teriid Hartmannula to the phyllopharyngean small 
subunit rRNA (SSUrRNA) gene database and have 
demonstrated the monophyly of four of these cyr-
tophorian families. 
 The Subclass Chonotrichia includes ectosym-
bionts, typically on the mouthparts and body 
appendages of a variety of marine and freshwater
 crustaceans . First described on a gammarid amphi-
pod by Stein (1851), their taxonomic history 
has had a checkered past (Mohr et al., 1970). 
Guilcher (1951) noticed their striking similarities 
to cyrtophorians in her study of chonotrich divi-
sion morphogenesis (Fig. 10.2). Ultrastructural 
analysis confirmed this common ancestry (Grain 
& Batisse, 1974; Fahrni, 1982). These sessile 
ciliates have a vase- or funnel-shaped apex that 
forms an atrial cavity. This cavity is lined by 
ciliature that we now know is predominantly a 
somatic ciliature (Grain & Batisse, 1974; Fahrni). 
Jankowski (1972b, 1973a, 1973b, 1975) divided 
the group on the basis of the kinds of reproduc-
tive budding . The Order Exogemmida produces 
daughter cells or buds externally and includes 
six families: Chilodochonidae , Filichonidae , 
 Heliochonidae , Lobochonidae , Phyllochonidae , 
and Spirochonidae . The Order Cryptogemmida pro-
duces buds , sometimes up to eight, within a crypt 
or brood pouch. It now also includes six families: 
 Actinichonidae , Echinichonidae , Inversochonidae , 
 Isochonidae , Stylochonidae , and the newest fam-
ily Isochonopsidae , described by Batisse and 
Crumeyrolle (1988). Jankowski (1972b, 1973a, 
1973b) and Mohr et al. have laid the modern 
groundwork for this group. Batisse (1994a) sug-
gested placing the Family Chilodochonidae into a 
monotypic order, but we await a test of this hypoth-
esis by gene sequence data. 
 The Subclass Rhynchodia has now been elevated 
from its ordinal level within the hypostomes . These 
predators of other ciliates and ectosymbionts of mol-
luscs and other invertebrates have a single suctorial 
tube or “ tentacle ”, appearing as a somewhat pointed 
protuberance at the anterior end of the cell (Fig. 
10.3). Ultrastructural study by Lom and Kozloff 
(1968, 1970) clearly established affinities with other 
 phyllopharyngeans : the somatic monokinetids were 
similar and the suctorial tube was lined by phyllae 
and enclosed elongate extrusomes called acmocysts 
or haptotrichocysts . Lynn and Small (2002) recog-
nized two orders, Order Hypocomatida and Order 
 Rhynchodida . Hypocomatids were transferred to 
this order based on the ultrastructural study of 
Hypocoma and the cladistic analysis of Grell and 
Meister (1982a). Hypocomatids , a monotypic order, 
are very similar to cyrtophorians with a dorsoven-
trally-flattened body, posterior adhesive region, and 
an external right kinety (Deroux, 1976b). Members 
of the Order Rhynchodida have considerably 
reduced somatic ciliature that may be divided into 
two fields leaving a large part of the ventral surface 
bare. We recognize two families within the order, 
the Ancistrocomidae and Sphenophryidae , which de 
Puytorac (1994b) and Lynn and Small (2002) recog-
nized as types for two monotypic suborders. Raabe 
(1970b) has provided the modern synthesis of this 
group, following the pioneering research of Chatton 
and Lwoff (1939a, 1939b, 1950) and Kozloff (1946, 
1955, 1961, 1965a). 
 The Subclass Suctoria has been one of the most 
puzzling groups in the phylum. Kahl (1930–1935) 
excluded it entirely from his treatment of the 
 ciliates. These ciliates, like the chonotrichs , are 
dimorphic with a tentacled, non-ciliated feeding 
stage or trophont and a ciliated dispersal stage 
or swarmer . Toxic extrusomes are the peculiar 
 haptocysts or phialocysts . Trophonts are not cili-
ated but have a field of kinetosomes typically near 
the contractile vacuole pore . Studying division 
morphogenesis, Guilcher (1951) confirmed the sug-
gestion of Fauré-Fremiet (1950a) that these ciliates 
are specialized “holotrichs”. Ultrastructural study 
by Batisse (1973) demonstrated that the somatic
monokinetids of the swarmer of Trematosoma were 
similar to those of other phyllopharyngeans . With 
a bewildering diversity of forms, and possibly sig-
nificant phenotypic plasticity,