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Abstract Ciliates in the Class NASSOPHOREA 
have played a pivotal role in phylogenetic schemes 
of the evolution of diversity of ciliates. Their 
 simplified oral structures were thought to represent 
the ancestral condition of the more well-developed 
oral polykinetids of oligohymenophoreans, hetero-
trichs, and spirotrichs. They are united by two 
ultrastructural features: alveolocysts are a presumed 
synapomorphy of all representatives, although they 
have not been observed yet in synhymeniids; and 
the nematodesmata of the nasse bear nematodesmal 
or X-lamellae, which are not found in the phyllo-
pharyngean cytopharyngeal basket. The highly 
developed nasse is used to ingest various “algae”, 
typically cyanobacteria such as Anabaena and 
Oscillatoria , whose natural populations in rare 
instances nassophoreans may control. The somatic 
cortex has a highly developed epiplasm. In addition 
to the nasse, there is a set of “oral” polykinetids 
that extends often around the body circumference 
as a linear assemblage called a frange or synhy-
menium. This is why stomatogenesis in these forms 
is considered mixokinetal because both somatic 
and oral kinetal elements are involved. The genetics 
of these ciliates is virtually unexplored so details 
of conjugation, mating type system, and nuclear 
 development remain to be discovered. 
Keywords Cyrtos, articulins, B-cartwheel, pavés, 
blue-green algae 
 The ancestors of Pseudomicrothorax , a ciliate now 
assigned to the Class NASSOPHOREA , were 
argued to have played a pivotal role in the evolu-
tion of the oligohymenophoreans (Corliss, 1958a, 
1958b; Thompson & Corliss, 1958). This was based 
on both the revelation by silver staining of three 
 adoral polykinetids , similar in position to those of 
the Class OLIGOHYMENOPHOREA , and in the 
mode of stomatogenesis. The “oral” ciliature of 
 nassophoreans is typically arranged as a hyposto-
mial “frange” , an extensive ventral band of more 
complex kinetids that courses slightly posterior 
to the cytostome and may extend onto the dorsal 
surface (Fig. 11.1). Fauré-Fremiet (1967a, 1967b) 
analyzed this ciliary “frange” and the adoral struc-
tures of other nassulid -like ciliates, Chilodontopsis , 
Nassulopsis , Nassula , Cyclogramma , Paranassula , 
and Pseudomicrothorax , and argued that, despite 
their diversity, these oral structures could all be 
considered homologues, justifying the recognition 
of a clade of nassulid ciliates. De Puytorac, Grain, 
Legendre, and Devaux (1984) demonstrated that 
cortical ultrastructural features related peniculines 
(e.g., Paramecium , Frontonia ) and nassulids , 
separating them from the hymenostomes (e.g., 
Glaucoma , Tetrahymena ). This analysis expanded 
on the previous, more restricted analysis of Lynn 
(1979a) who had shown that nassulids , peniculines , 
and hymenostomes were all related using phyl-
lopharyngeans as the outgroup taxon: nassulids 
were the basal clade of the three (Lynn, 1979a). 
Sequence analyses of the large and small subunit 
rRNA genes have confirmed a close relationship 
between nassulids , peniculines , and hymenostomes 
(Baroin-Tourancheau, Villalobo, Tsao, Torres, 
& Pearlman, 1998; Bernhard, Leipe, Sogin, & 
Schlegel, 1995; Strüder-Kypke, Wright, Fokin, & 
Lynn, 2000b). Histone gene sequence similarities 
 Chapter 11 
 Subphylum 2. 
INTRAMACRONUCLEATA: Class 5. 
NASSOPHOREA – Diverse, Yet Still 
Possibly Pivotal 
Fig. 11.1. Stylized drawings of representative genera from the orders in the Class NASSOPHOREA . The synhyme-
niids Nassulopsis , Chilodontopsis , and Scaphidiodon . The nassulid Obertrumia
related nassulids and hymenostomes (Bernhard 
& Schlegel, 1998) although the α-tubulin gene 
sequence of Zosterodasys does not support this rela-
tionship (Baroin-Tourancheau et al., 1998). Overall, 
the earlier conception that nassulid -like ciliates 
were ancestors for the oligohymenophoreans still 
seems a reasonable view (see below Division and 
Morphogenesis ). 
 Ciliates in this class are typically holotrichous. 
Larger nassulids , which can be >200 µm in length, 
are densely ciliated. However, some of the smaller 
 microthoracids , which may be about 10 µm in 
length, can exhibit regions of the cortex that are 
barren of cilia, including the dorsal surface in 
 discotrichids . Scaphidiodon is tentatively placed in 
this class, although it has three features that relate it 
to the cyrtophorian phyllopharyngeans : (1) a non-
ciliated dorsal surface; (2) right somatic kineties 
that arch over the anterior end onto the left ventral 
surface and terminate on the anterior suture; and 
(3) a podite -like appendage at the posterior end 
(Dragesco, 1965). The pattern of the somatic cili-
ation of other nassophoreans is also similar to that 
of cyrtophorians as the right somatic kineties may 
arch over the oral region onto the left ventral surface
(Deroux, 1994b). 
 Small and Lynn (1981) were the first to elevate 
this group to the class level, establishing the Class 
 NASSOPHOREA . The class derives its name from 
the French “nasse” meaning basket and the Greek 
phoros meaning to bear. This refers to the com-
plex cytopharyngeal basket of nematodesmata that 
are used in feeding. Original descriptions of the 
ultrastructure of the nasse (Fauré-Fremiet, 1962a) 
stimulated later research on the structure, function,
and development of this complex microtubular 
apparatus in Nassula (Tucker, 1968, 1970a, 1970b). 
Earlier demonstration of the thick epiplasm in 
Pseudomicrothorax (Fauré-Fremiet & André, 1967) 
has led to the discovery of a novel class of pro-
teins, the articulins , which are found in ciliates and 
 euglenoid flagellates (Huttenlauch & Stick, 2003; 
Huttenlauch, Peck, & Stick, 1998a). Cellular and 
biochemical research has been possible because 
these ciliates can be easily grown on filamentous 
 cyanobacteria (Peck, 1977b; Tucker, 1968). 
Members of the class are united by two synapomor-
phies: (1) the presence of alveolocysts , extensions 
of the cortical alveoli into the cytoplasm; and (2) the 
presence of nematodesmal or X lamellae , accompa-
nying the nematodesmata of the nasse (Eisler, 1989; 
Eisler & Bardele, 1983). These two features are 
presumed to be present in synhymeniids , although 
ultrastructural analysis of their nasse is needed to 
confirm this (see Taxonomic Structure ). 
 11.1 Taxonomic Structure 
 Corliss (1979) placed nassophorean ciliates 
in the Subclass Hypostomata of the Class 
 KINETOFRAGMINOPHORA based on the pres-
ence of a hypostomial “frange” that extends to 
varying degrees across the ventral surface of the 
cell and that may ultimately be restricted to the oral 
region. Small and Lynn (1981, 1985) were led by 
similarities in the somatic kinetids and extrusomes 
to include synhymeniids , nassulids , microthorac-
ids , peniculines , and hypotrichs in their newly 
conceived Class NASSOPHOREA . Gene sequence 
data have now refuted a close relationship of 
 hypotrichs with these taxa and demonstrated that 
 peniculines are a basal clade in the oligohy-
menophorean radiation (e.g., Baroin-Tourancheau, 
Delgado, Perasso, & Adoutte, 1992; Lynn & Sogin, 
1988; Strüder-Kypke et al., 2000b). 
 Fauré-Fremiet (1967a) set the conceptual perspec-
tive for phylogeny within this class by proposing a 
phylogenetic transformation series for the ciliary 
 “frange” , the French for fringe. Some synhymeniids 
are considered to represent its ancestral state: a 
transverse line of dikinetids, not well differentiated 
from the adjacent somatic monokinetids, extend-
ing completely across the ventral surface and onto 
the dorsal surface (Fig. 11.1) (e.g., Zosterodasys , 
formerly Chilodontopsis ). It is imagined that these 
dikinetids became polymerized into the “pavés” ,
French meaning paving-stone or tile, or small 
polykinetids (e.g., some Nassulopsis species). These 
polykinetidsthen gradually decreased in number as 
they became increasingly restricted to the left side 
of the ventral surface (e.g., some Nassula species) 
and then to the left side of the oral region. This ulti-
mately resulted in hymenostome -like ciliates with 
three oral polykinetids (Fig. 11.2) (i.e., Furgasonia , 
Pseudomicrothorax ) – a phylogenetic hypothesis 
that now requires more extensive testing by gene 
sequence data! 
 It is clear that there is a significant amount of 
diversity in the “oral” structures of these ciliates, 
and this has led to substantial high level split-
ting of the taxa. The French researchers have 
11.1 Taxonomic Structure 235
236 11. Subphylum 2. INTRAMACRONUCLEATA: Class 5. NASSOPHOREA
recognized this by supporting six orders within a 
Subclass Nassulia (Deroux, 1994b; de Puytorac, 
1994a). Jankowski (1968a) recognized two subor-
ders within his Order Ambihymenida . Given that 
relatively little taxonomic research has focused on 
these ciliates while only two genera have received 
the bulk of research attention, we have remained 
conservative. Following Lynn and Small (2002), 
we include three orders in this class and anxiously 
await data derived from silver staining, electron 
microscopy, and gene sequences on the distinctive-
ness of the aberrant genera included in this class. 
 The Order Synhymeniida includes forms whose 
ciliary fringe or synhymenium is composed of 
dikinetids or small polykinetids, typically of 4–6 
kinetosomes. The synhymenium extends from the 
right postoral body surface sometimes onto the 
left dorsal body surface. We include four families: 
 Nassulopsidae , Orthodonellidae , Scaphidiodont-
idae , and Synhymeniidae . Deroux, Iftode, and Fryd 
(1974) and Deroux (1978) laid the modern ground-
work for this group, based on Jankowski (1968a). 
Sola et al. (1990a) have speculated that Nassulopsis
might be removed from this order and placed in 
the Order Nassulida . We await gene sequence data 
before making this transfer. 
 The Order Nassulida includes taxa whose syn-
hymenium is composed of obvious polykinetids, 
restricted to the left ventral and sometimes dorsal 
surface. In some forms, these polykinetids have been 
reduced to three, which are restricted to the left side 
of the cytostome. Nevertheless, there is considerable 
Fig. 11.2. Stylized drawings of representative genera from the orders in the Class NASSOPHOREA . The microtho-
racids Pseudomicrothorax , Microthorax , and Discotricha
variation from this “typical” tripartite left oral pat-
tern: Enneameron (formerly Nassula brunnea ; see 
Jankowski, 1968a) may have more than five rows 
of monokinetids in an oral atrium (Fauré-Fremiet, 
1962a) while Parafurgasonia appears to have 
a paroral and a single oral polykinetid (Foissner 
& Adam, 1981). These variations have led some 
to elevate included families and genera to ordinal 
rank (e.g., Deroux, 1994b; Grain, Peck, Didier, 
& Rodrigues de Santa Rosa, 1976; de Puytorac, 
1994a). We include conservatively three families: 
 Furgasoniidae , Nassulidae , and Paranassulidae . 
 The third order, the Microthoracida , includes 
typically small ciliates with sparse somatic ciliation
and a cyrtos that is reduced in size. Although three 
 adoral polykinetids are typical, there is consider-
able variation among genera (e.g., Foissner, 1985a). 
 Fibrous trichocysts with anchor-like tips are con-
sidered characteristic of the order. We include 
three families in the order: Leptopharyngidae , 
 Microthoracidae , and Discotrichidae . Members of 
the latter family, which is monotypic, are highly 
aberrant: Discotricha has a non-ciliated dorsal 
surface, ventral somatic polykinetids that are cirrus-
like, and extrusomes that do not have anchor-like 
tips (Foissner, 1997a; Tuffrau, 1954; Wicklow 
& Borror, 1977). Gene sequence data are clearly 
needed here! 
 We place one family incertae sedis in this class. 
We have removed the Colpodidiidae from the 
Order Nassulida , where it was placed by Lynn and 
Small (2002), as these species lack a cyrtos and 
have highly aberrant oral ciliature, and placed it 
incertae sedis in the Class NASSOPHOREA . 
 11.2 Life History and Ecology 
 Nassophoreans are only rarely observed in high 
abundances. Most species are found in freshwaters 
or soils with fewer in brackish and marine habitats. 
However, they have been found on all continents. 
 Microthoracids are typical of soils in Europe 
(Foissner, 1981a, 1998a) and Africa (Buitkamp, 
1977; Foissner, 1998a, 1999a). Nassulids and 
 synhymeniids have been described from marine 
and freshwaters in Europe (Agamaliev, 1967; 
Alekperov, 1984; Burkovsky, 1970; Czapik & 
Jordan, 1976; Finlay & Maberly, 2000), Africa 
(Dragesco, 1965; Njiné, 1979), Asia (Ozaki & 
Yagiu, 1941; Song & Wei, 1998), North America 
(Borror, 1972; Bullington, 1940), and Antarctica 
(Thompson, 1972). 
 The larger nassulids and microthoracids 
appear to feed preferentially on cyanobacteria , 
such as Anabaena , Aphanizomenon , Oscillatoria , 
Phormidium , and Synechococcus (Canter, Heaney, 
& Lund, 1990; Peck, 1985; Tucker, 1978). They 
do show some feeding preferences : Nassula aurea
was reported never to graze Gomphosphaeria
and Microcystis (Canter et al., 1990) while 
Pseudomicrothorax dubius rarely ingested some 
Anabaena species (Peck, 1985). Both surface 
charges and phagocytosis-specific molecules on 
the cyanobacterial filaments are necessary to 
explain these feeding preferences (Kiersnowska, 
Peck, & de Haller, 1988). Feeding behavior of 
Pseudomicrothorax has been divided into two 
phases: (1) a contact swimming phase during 
which the ciliate guides itself along the cyano-
bacterial filament , typically finding an end to 
begin ingestion; and (2) a phagocytosis phase that 
involves first attachment and then ingestion. Ca 2+
influx is probably essential for both the attach-
ment phase of phagocytosis and for the exocytosis 
of lysosomes during the initial ingestion of the 
filaments (Peck & Duborgel, 1985). Some slightly 
starved Nassula species show a negative photo-
taxis to light when they also possess a conspicuous 
stigma-like structure. How this phototaxis is medi-
ated has not been determined although its function 
is presumed to lead these ciliates towards slightly 
illuminated regions that are preferred by cyano-
bacteria (Kuhlmann & Hemmersbach-Krause, 
1993b). Microthoracids are typically bacteri vorous 
(Foissner, Berger, & Kohmann, 1994) and have 
been reported from the activated sludge biotope 
(Leitner & Foissner, 1997a). 
 Deroux (1994b) remarked that many nassopho-
reans harbor Chlorella symbionts. However, there 
has been little research on this relationship. 
 Nassophoreans are likely eaten by a variety 
of invertebrates, but records of this are scarce. 
Addicot (1974) implied that Leptopharynx might be 
eaten by mosquito larvae while Braband, Faafeng, 
Källqvist, and Nilssen (1983) observed fish fry 
and copepods to feed on Nassula . The suctorians , 
Podophrya (Canter et al., 1990; Fauré-Fremiet, 
1945) and Sphaerophrya (Clément-Iftode, 1967), 
are repeatedly observed as predators of nassulids . 
11.2 Life History and Ecology 237
238 11. Subphylum 2. INTRAMACRONUCLEATA: Class 5. NASSOPHOREA
 Encystment is typical of nassophoreans , which 
are stimulated to do so by the lack of food (Beers, 
1966a; Canter et al., 1990; Mulisch & Hausmann, 
1989). The cyst wall is composed of three layers 
with the mesocyst layer having chitin microfibrils, 
as has also been observed in heterotrichs (Mulisch 
& Hausmann, 1989). 
 11.3 Somatic Structures 
 Synhymeniids and nassulids are typically larger 
ciliates, holotrichously ciliated with cylindrical 
bodies. Microthoracids are smaller, often flattened, 
and with fewer somatic kineties whose kinetosomes 
may be more widely dispersed or even aggregated 
into polykinetid-likeorganellar complexes (e.g., 
Discotricha ) (Figs. 11.1, 11.2). 
 The cell surface of these ciliates is undoubt-
edly covered by a glycocalyx , although it has only 
been clearly demonstrated in Pseudomicrothorax
(Hausmann, 1979). Underlying the plasma membrane 
is a typical alveolar layer with the unusual feature that 
the alveoli may send invaginations through the epi-
plasm into the cortex of the ciliate. These alveolocysts 
are typically paired and on either side of the somatic 
kinetids (Eisler, 1989; Eisler & Bardele, 1983). We 
recognize these structures as a synapomorphy for the 
class NASSOPHOREA although they remain to be 
demonstrated in synhymeniids . 
 Some nassophoreans have a conspicuous epi-
plasm (e.g., Pseudomicrothorax – Peck, 1977b; 
Furgasonia – Eisler, 1988; Nassula – de Puytorac 
& Njiné, 1980; Tucker, 1971a). Pseudomicrothorax
can be prepared as an “epiplasmic” ghost , retaining 
its cell shape without any of the cell membranes or 
cortical microtubular structures – a clear demon-
stration of the shape-maintaining function of the 
 epiplasm (Peck, 1977b; Peck, Duborgel, Huttenlauch, 
& Haller, 1991). Immunocytochemistry has demon-
strated that proteins from the ciliate epiplasm share 
common epitopes with those proteins from the 
pellicles of euglenoids and dinoflagellates (Vigues, 
Bricheux, Metivier, Brugerolle, & Peck, 1987). 
The epiplasm , especially adjacent to the inner alve-
olar membrane, has higher concentrations of glyco-
proteins (Curtenaz & Peck, 1992; Huttenlauch 
& Peck, 1991). The middle layer is composed 
of articulins , a novel kind of cytoskeletal protein 
found also in euglenoids , which is characterized 
by unique repeating valine-proline-valine (VPV) 
motif, presumed to provide stability to this layer 
(Huttenlauch, Geisler, Plessmann, Peck, Weber, & 
Stick, 1995; Huttenlauch, Peck, Plessmann, Weber, 
& Stick, 1998b). In addition, another class of pro-
teins, the epiplasmins , are also found in the micro-
thoracid epiplasm and related to epiplasmins in the 
 peniculine epiplasm . Epiplasmins , although rich in 
valine and proline, do not show the VPV-motif of 
the articulins (Coffe, Le Caer, Lima, & Adoutte, 
1996; Huttenlauch et al., 1998a). 
 The somatic kinetid of the nassophoreans has 
been resummarized by Eisler (1988). Monokinetids 
can now be characterized as follows: a divergent 
postciliary ribbon at triplet 9; an anterior and 
laterally-directed kinetodesmal fibril at triplets 
5 and 6; and a small tangential transverse ribbon 
at triplets 3 and 4, arising from some dense material
(Figs. 11.3, 11.4) (Lynn, 1991). Dikinetids can 
occur: a posterior ciliated kinetosome with the 
typical fibrillar pattern is connected to an ante-
rior ciliated kinetosome with a single postciliary 
 microtubule and sometimes a transverse ribbon 
(Fig. 11.3) (Eisler, 1988). The kinetosomes of nas-
sulids have a distal B-cartwheel and may also have 
a proximal and standard A-cartwheel , while micro-
thoracids may lack both cartwheels (Eisler; Njiné 
& Didier, 1980; Peck, 1977b; Tucker, 1971a). 
 The contractile vacuole system of nassophore-
ans is a Type A system (Patterson, 1980) with the 
 contractile vacuole surrounded by a spongiome of 
irregularly arranged tubules, 20–80 nm in diameter 
(Hausmann, 1983; Prelle, 1966). Microthoracids 
may have an elongated contractile vacuole pore 
canal that extends into the cytoplasm. 
 Nassophoreans have rod-shaped extrusomes that 
have been called fibrocysts or fibrous trichocysts 
(Hausmann, 1978). Their structure and devel-
opment have been particularly well studied in 
Pseudomicrothorax . Its trichocysts have anchor-
like tips that splay out upon ejection. The 50-nm 
periodicity of the ejected shaft is very similar 
to that of the ejected trichocysts of Paramecium
(Hausmann, 1978), which also show remarkable 
similarities in their constituent proteins (Eperon 
& Peck, 1993). Fibrocyst development occurs in 
Golgi vesicles and involves the unusual fusion of 
two types of vesicles, one containing shaft precur-
sors and the other containing tip precursors (Peck, 
Swiderski, & Tourmel, 1993a, 1993b). Once devel-
oped, the trichocyst docks in the cortex by local-
ized dissolution of the epiplasm and penetration 
of the alveolar layer before contacting the inner 
surface of the plasma membrane (Eisler & Peck, 
1998). Although classified here as a microthoracid , 
Discotricha does not have anchor-like tips on its 
 extrusomes (Wicklow & Borror, 1977). Does this 
mean that it is truly not a microthoracid although 
its oral structures suggest otherwise (see below)? 
 11.4 Oral Structures 
 Nassophoreans possess some kind of oral basket 
of nematodesmata – “nasse” or cyrtos , which 
can be quite conspicuous and well-developed. 
Ciliary structures may be associated with this 
basket in nassulids and microthoracids . The 
 nassulid Furgasonia has a paroral of stichodyads 
and three adoral polykinetids (Figs. 11.1, 11.2) 
(Eisler, 1988). In Pseudomicrothorax , the paroral 
 dikinetids dissociate during stomatogenesis so that 
“posterior” kinetosomes remain associated with the 
 nematodesmata while a few “anterior” kinetosomes 
that are not resorbed remain as “residual kineto-
somes” posterior to the cytostome (Peck, 1975; 
Thompson & Corliss, 1958). In most Nassula
species, the “oral” polykinetids course on the left 
ventral surface, posterior to the cytostome, and 
may extend onto the dorsal surface. 
 “Oral” structures in the synhymeniids differ 
from that of nassulids in two ways. First, they 
extend across the entire ventral surface, even encir-
cling the entire body as the so-called synhymenium 
(e.g., Nassulopsis ). Second, they are composed of 
dikinetids or polykinetids of typically no more than 
six kinetosomes (Fig. 11.1). However, in scaphidi-
odontids and orthodonellids , the extension of the 
 synhymenium into the anterior suture recalls the 
overall pattern of cyrtophorians (cf. Figs. 10.1, 
11.1) (Deroux, 1994b). There has been no detailed 
ultrastructural description of the synhymenium
kinetids nor of the cytopharyngeal basket of syn-
hymeniids to determine that it shows strong simi-
larities to other nassophoreans (i.e., presence of 
 nematodesmal lamellae ). 
 On the other hand, several studies have detailed 
 nassulid and microthoracid oral ultrastructure. 
Eisler’s (1988) detailed study has demonstrated 
that the kinetosomes of the paroral dikinetids of 
Furgasonia and probably Nassula are oriented 
perpendicular to each other: the right or “anterior” 
kinetosome is oriented in the long axis of the 
paroral while the left or “posterior” kinetosome is 
oriented at right angles to the paroral. The Z or cys-
tostomal lamellae arise from the postciliary ribbons 
of the “posterior” kinetosomes (Eisler, 1988). The 
 oral polykinetids of nassulids are square-packed 
organellar complexes of three rows. Kinetosomes 
of the posterior row bear postciliary ribbons 
and all kinetosomes bear presumably a single 
 transverse microtubule at triplet 4. Parasomal sacs 
are distributed throughout the structure (Eisler, 
1988; de Puytorac & Njiné, 1980). 
 The nassophorean cytopharyngeal basket or 
 cyrtos has received the most detailed analysis by 
cell biologists who were attracted to it as perhaps the 
most complicated microtubular organellar complex 
Fig. 11.3. Schematics of the somatic kinetids of the Class 
 NASSOPHOREA . ( a ) Monokinetid of Pseudomicrothorax . 
(b ) Monokinetid of Furgasonia . c . Dikinetid of Furgasonia . 
(d ) Monokinetid of Nassula . ( e ) Dikinetid of Nassula (from 
Lynn, 1981, 1991) 
11.4 Oral Structures 239
240 11. Subphylum 2. INTRAMACRONUCLEATA: Class 5. NASSOPHOREA
of any cell! Eisler (1988) has noted that nassulids 
and microthoracids have the X or nematodesmal 
 lamellae , which are absent in phyllopharyngeans. 
These lamellae develop from the marginal micro-
tubules of the nematodesmata, forming a ribbon 
and eventually gaining dynein-like arms. The cyrtos
of nassulids has both Y or subcytostomal lamellae 
and, as noted above, Z or cytostomal lamellae , 
neither of which are found in the microthoracid 
 cyrtos (Eisler, 1988). 
 The structure and function of the cytopharyngeal 
basket of nassophoreans has been described in detail 
for Nassula (Tucker, 1968) and Pseudomicrothorax
(Hausmann & Peck, 1978). Microfilaments bind 
the nematodesmata at the oral or distal end and 
may extend along much of the length of the cyrtos 
while a denser annulus binds the nematodesmata 
of Nassula at a more proximal level. Displacement 
of the nematodesmata, possibly by contraction of 
the microfilamentous systems facilitates ingestion 
of the cyanobacterial filaments . The arm-bearing 
microtubules of the X or nematodesmal lamel-
lae have been implicated in endocytosis of these 
filaments. Tucker (1978) argued that the arms 
in Nassula act indirectly on a highly gelated 
cytoplasm that is strongly associated with the 
 food vacuole membrane. Hausmann and Peck 
(1979) argued that the arms in Pseudomicrothorax
Fig. 11.4. Somatic cortex of a typical nassophorean interpreted based on the somatic cortex of Pseudomicrothorax . 
(Modified after Peck, 1977b.)
are associated with microfilaments that interact 
directly with the food vacuole membrane, trans-
porting it inwards at up to 15 µm sec −1 . Subsequent 
research on Pseudomicrothorax has confirmed the 
presence of actin , α-actinin , and ATPase in the 
basket, implicating an actin-based motility system 
in feeding (Hauser & Hausmann, 1982; Hauser, 
Hausmann, & Jockusch, 1980). 
 Hundreds of square micrometers of food vacu-
ole membrane must be formed in minutes during 
the ingestion of cyanobacterial filaments in these 
ciliates. Both Tucker (1978) and Hausmann and 
Peck (1979) have observed cytoplasm and vesicles 
entering the cyrtos between the nematodesmata at 
its oral or distal end. Many of these vesicles are 
probably primary lysosomes that serve a double 
function of providing membrane for the expanding 
food vacuole and hydrolases to begin the very rapid 
digestion of their food (Peck & Hausmann, 1980). 
Subsequent folding of the food vacuole mem-
branes and vesiculation of the food vacuole may 
facilitate resorption of nutrients (Hausmann, 1980; 
Hausmann & Rüskens, 1984). Thus, we have now 
detailed knowledge of how oral structures function 
in both nassulids and microthoracids . How similar 
is the process in synhymeniids? 
 11.5 Division and Morphogenesis 
 Nassophoreans typically divide while swimming 
freely. The parental oral structures are almost com-
pletely dedifferentiated and then redifferentiated in 
synchrony with those of the opisthe (e.g., Eisler & 
Bardele, 1986; Tucker, 1970a). Foissner (1996b) 
established mixokinetal stomatogenesis to character-
ize division morphogenesis in these ciliates: both 
the parental oral apparatus and the somatic ciliature 
simultaneously participate in stomato genesis – a mix -
ture of origins. Broadly, the parental paroral gives 
rise to the opisthe paroral while the synhymenium or 
 hypostomial fringe is derived from somatic kineties. 
 Eisler (1989) and Eisler and Bardele (1986) have 
provided the most detailed comparative analysis of 
 stomatogenesis in the nassophoreans (Fig. 11.5). In 
 nassulids , the parental paroral splits longitudinally 
to form a new Kinety 1' from its right kinetosomes 
and a new paroral from the left kinetosomes. The 
kinetosomes of the paroral serve as nucleation sites 
for the development of the oral nematodesmata, 
which subsequently close to form the circular pali-
sade of the differentiated cyrtos (Eisler & Bardele, 
1986; Tucker, 1970a). The microtubule nucleating 
template that develops in association with these 
oral kinetosomes probably controls the shape and 
pattern of the growing nematodesmata (Pearson & 
Tucker, 1977; Tucker, Dunn, & Pattisson, 1975). 
 Eisler and Bardele (1986) interpreted stomato-
genesis in the microthoracids using their model 
for nassulid stomatogenesis . They concluded that 
the paroral and kinetal segments of the opisthe in 
Pseudomicrothorax and Leptopharynx originate 
from the parental paroral and are retained as the 
so-called “residual kinetosomes” at the next cell 
division. Peck (1975) and Njiné (1980) interpreted
their origin to be from somatic Kinety 1. Regardless 
of this difference of opinion, the paroral kinetosomes 
play a key role in formation of the basket while 
the adoral polykinetids assume a highly similar 
relationship with the cytostome, strongly support-
ing the ultrastructural similarities in somatic and 
oral structures discussed above. 
 The stomatogenesis of the highly unusual micro-
thoracid Discotricha may also be mixokinetal 
(Foissner, 1996b). Wicklow and Borror (1977) ten-
tatively concluded that post-buccal Kinety 1 par-
ticipated in stomatogenesis . This kinety itself may 
ultimately be an “oral” kinety, homologous to the 
 “residual kinetosomes” of other microthoracids . 
Further study of the stomatogenesis of this highly 
unusual ciliated is warranted as is investigation of 
 stomatogenesis in the synhymeniids . 
 Cytokinesis , at least in Nassula , coincides with 
the development of a contractile ring of microfila-
ments that presumably constrict against a girdle of 
several thousand longitudinally oriented micro-
tubules, which are embedded in the epiplasm 
(Tucker, 1971b). 
 11.6 Nuclei, Sexuality 
and Life Cycle 
 There has been relatively little research on these 
aspects of the biology of nassophoreans . The 
single macronucleus is homomerous and typi-
cally globular to ellipsoid in shape (Figs. 11.1, 
11.2). Species of smaller cell-size have one 
 micronucleus while larger cells may have multi-
ple micronuclei (e.g., Nassulopsis species – Sola 
11.6 Nuclei, Sexuality and Life Cycle 241
242 11. Subphylum 2. INTRAMACRONUCLEATA: Class 5. NASSOPHOREA
et al., 1990a). Intranuclear microtubules are found 
during division of both the micronucleus and the 
 macronucleus , and membrane bridges link micro- 
and macronuclei during late anaphase and early 
telophase, coordinating karyokinesis of the two 
nuclei (Tucker, 1967). Raikov (1982) character-
ized the nassulid macronucleus as a polyploid 
subnuclear type because the chromatin apparently 
aggregates as diploid sub units in both Nassula and 
Nassulopsis and whole genomes are believed to 
segregate at macronuclear division . These conclu-
sions based on early work need to be verified by 
modern techniques. 
 To our knowledge, the detailed cytology of 
 conjugation has not been described for any nas-
sophorean except for four stages illustrated by 
Raikov (1972) who reported that conjugation in 
Nassula might be seasonal. The pattern of conjuga-
tion appears to be typical of the ciliates. As in the 
 cyrtophorians , the cyrtos detaches from the cortex 
and is resorbed. During meiosis in Nassula , there 
are three maturation divisions, two meiotic and one 
mitotic. The micronucleus at zygotene assumes 
a “parachute stage” , a stage homologous to the 
 “crescent stage” in other ciliates. The conjugation 
 “fusion zone” in Nassula appears as a region of 
homogeneous cytoplasm that encloses the four 
 gametic nuclei . Fertilization occurs in this cyto-
plasmic region without apparent migration of the 
 gametic nuclei (Fig. 34 in Raikov, 1972). In addi-
tion to details on the cytology, we can only assume 
that there is a life cycle and genetics of mating type 
determination as for other ciliates. But what it is 
and how it is determined remain among the many 
questions to be answered for this possibly pivotal 
group of ciliates. 
Fig. 11.5 Division morphogenesisof the nassulids A Furgasonia and B Nassula . Stomatogenesis in both these 
genera is mixokinetal , initially involving kinetosomal proliferation from both somatic and oral kinetosomes ( a ). In 
Furgasonia , assembly of the adoral structures involves proliferation from right to left ( b ), and as the developing oral 
polykinetids rotate ( c ), the differentiation is completed from anterior to posterior and right to left ( d ). In Nassula , pro-
liferation ( b ) and assembly ( c, d ) of the polykinetids also occurs from right to left. (from Eisler & Bardele, 1986.)