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and the 
tentacle primordia are in the “posterior” of the cell, 
defined by its direction of swimming! Curry and 
Butler (1982) described the early proliferation of 
non-ciliated kinetosomes in the shallow embryonic 
cavity of Discophrya to form the kineties of the 
 swarmer . Budding in Tokophrya has also been studied
by electron microscopy. Its bud is distinguished by 
kineties that encircle the ovoid cell body. A so-called
“ divergent kinety ” remains isolated in the “posterior”
half of the cell (Fig. 10.6) (Guilcher, 1951; Noble, 
1932; Suárez, Guinea, & Fernández-Galiano, 
1987b). Could this “ divergent kinety ” in fact be 
the homologue of the external right kinety of cyrto-
phorians ? The primordial field of kinetosomes also 
occurs near the contractile vacuole pore in Acineta
and Tokophrya . As replication proceeds, the brood 
pouch enlarges by internal growth of the parental 
pellicle, which also forms the birth pore (Bardele, 
1970; Millecchia & Rudzinska, 1970). 
 The life span of a swarmer lasts from minutes to 
hours prior to settling. It does not feed during this 
period and is presumably stimulated to settle in a par-
ticular place by chemical cues. Walker and Roberts 
(1988) noted that swarmers of Dendrocometes are 
probably triggered to settle near conspecifics on 
the gills of the amphipod Gammarus . Upon settling 
metamorphic changes are quite rapid: a basal disc 
is secreted, a stalk is formed; cilia are resorbed; and 
 tentacles begin to grow and extend (Bardele, 1970; 
Fernàndez-Leborans & Tato-Porto, 2002; Hascall 
& Rudzinska, 1970; Henk & Paulin, 1977). After 
formation of the basal disc , the Acineta swarmer 
can produce a 70 µm long stalk in 5–10 min by 
secretion of material from scopuloid vesicles into 
a canal-like invagination of the body (Bardele, 
1970). After the stalk reaches its mature length, 
the cell body of the adult Acineta is enclosed in 
a lorica , which is formed by the migration of the 
perimeter of the scopuloid up over the surface of 
the cell body, accompanied by continued secretion 
of material (Bardele, 1970). 
10.5 Division and Morphogenesis 229
230 10. Subphylum 2. INTRAMACRONUCLEATA: Class 4. PHYLLOPHARYNGEA
 10.6 Nuclei, Sexuality and Life 
Cycle
 Phyllopharyngeans exhibit nuclear dimorphism, 
but the four subclasses are separated into two 
groups on the basis of a macronuclear feature. Like 
all other ciliates, rhynchodians and suctorians have 
 homomerous macronuclei – a potential indicator of 
their ancestral nature? Cyrtophorians and chonot-
richs have heteromerous macronuclei (Karadzhan, 
1976; Lom & Corliss, 1971). Heteromerous macro-
nuclei have two basic parts: the orthomere (orthos, 
Greek – right, proper; meros, Greek – part) is a 
“proper” part because it is DNA-rich and contains 
nucleoli; and the paramere (para, Greek – beside) 
is DNA-poor (Raikov, 1982). The typical arrange-
ment is called juxtaposed in which the orthomere 
is beside the paramere (Figs. 10.1, 10.2). However, 
in some species, the arrangement is concentric 
with the orthomere surrounding the paramere (Fig. 
10.1) (Fauré-Fremiet, 1957; Radzikowski, 1985). 
Macronuclear shape is most typically globular 
or ellipsoid (Figs. 10.1–10.6). However, some 
large suctorians , like some Ephelota species, can 
have complex ramified or ribbon-like macronuclei. 
There is usually one ellipsoid micronucleus. Both 
 macronuclear and micronuclear division are accom-
plished by intranuclear microtubules (Millecchia & 
Rudzinska, 1971). 
 Reminiscent of the spirotrichs , chromosomes 
are fragmented in the macronuclei of phyllopha-
ryngeans . This has been demonstrated at least in 
the Subclasses Cyrtophoria and Suctoria (Lahlafi 
& Metenier, 1991; Riley & Katz, 2001). The gene-
sized pieces , ranging from 2–70 kb in size, includ-
ing ribosomal DNA, are located in the orthomere
(Radzikowski & Steinbrück, 1990; Steinbrück, 
Radzikowski, Golembiewska-Skoczylas, & 
Sapetto-Rebow, 1995). Raikov (1982) reported that 
 cyrtophorians and chonotrichs also show a “ repli-
cation-like band ” in the macronucleus , reminiscent 
of that of the spirotrichs , but it has not yet been 
substantiated by autoradiography that DNA repli-
cation occurs in this region. As in the spirotrichs , 
development of the fragmented condition occurs 
as the macronuclear anlage differentiates after 
 conjugation . A polytene chromosome stage has 
been observed in Chilodonella (= Trithigmostoma ) 
cucullulus between 50–75 h after conjugation 
(Radzikowski, 1973). In a related Chilodonella
species, polytene chromosomes have not been 
seen by light microscopy presumably because 
of a higher degree of chromosome despiraliza-
tion that is only visible by electron microscopy 
(Pyne, 1978; Pyne, Ruch, Leeman, & Schneider, 
1974). Although there is no apparent DNA-
diminution stage during anlage development, as 
in the spirotrichs , over 30% of the macronuclear 
DNA is eliminated during the first cell division of 
the exconjugants (Radzikowski, 1979). In a further 
molecular similarity to the spirotrichs and oligot-
richs , cyrtophorians have internally eliminated 
sequences (IESs) that are located in the coding 
region of micronuclear genes, but flanked by a dif-
ferent direct repeat – YGATTSWS (Katz, Lasek-
Nesselquist, & Snoeyenbos-West, 2003). 
 Conjugation has been reported in members from 
all four subclasses of phyllopharyngeans . The 
micronucleus typically undergoes three matura-
tion divisions and there is typically one division 
of the synkaryon following conjugation (Raikov, 
1972). Conjugation can be between conjugants 
equal in size (i.e., isogamontic in Chilodonella
– MacDougall, 1935; Tokophrya – Noble, 1932; 
Colgin-Bukovsan, 1977) or unequal in size (i.e., 
 anisogamontic in Spirochona – Tuffrau, 1953). 
 Anisogamontic conjugation occurs often in chonot-
richs and suctorians , and is usually accompanied 
by total fusion of the conjugants rather than tempo-
rary fusion. Temporary, total isogamontic , and total 
 anisogamontic conjugation can occur within one 
family of suctorians (i.e., Discophryidae) (Raikov, 
1972). Fusion of cells typically occurs in the oral 
region, when it can be identified (e.g., see Dobrza
ska, 1961; MacDougall, 1935; Tuffrau, 1953). 
However, some rhynchodians fuse in the posterior 
region (de Puytorac, 1994b). 
 As sessile organisms, suctorians prepare to con-
jugate by touching tentacles. Stalked species then 
approach each other by changes in the cell shape, 
often involving extension of a pseudopodium-like 
process. The two conjugants of Tokophrya only 
temporarily fuse (Noble, 1932), while the smaller 
conjugant or microgamont of Ephelota leaves its 
stalk and totally fuses with the macrogamont (Grell 
& Meister, 1984). Stalkless species can produce a 
special conjugation bridge into which the micro-
nuclei migrate (e.g., Heliophrya – Lanners, 1973). 
The conjugation bridge between cells is formed by 
the fusion of the epiplasmic layers of the two cells 
(Grell & Meister, 1984; Lanners, 1978). Similar 
to what has been described for Tetrahymena
(Orias, Hamilton, & Orias, 1983), positioning and 
exchange of gametic micronuclei is facilitated by a 
cytoskeletal meshwork composed of microtubules 
and microfilaments (Lanners & Rudzinska, 1986; 
Hanke-Bucker, Lanners, & Hauser, 2000). 
 Relatively few studies have been done on the fac-
tors influencing conjugation in phyllopharyngeans 
and on the genetics of this process. It is likely that 
host-mediated factors may influence conjugation 
in symbiotic forms, but no definitive experiments 
have yet demonstrated this. Exhaustive searching 
has not revealed stable opposite mating types in 
Chilodonella : all isolates so far undergo intraclonal 
conjugation . Often this leads to abortive conju-
gation and retention of the old macronucleus in

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