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1979; Lynn, 1980) do not form postcili-
odesmata , while redescriptions of the reichenowel-
lid Balantidioides suggest that it has affinities to the 
 spirotrichs (Foissner et al., 1982). While SSrRNA 
gene sequences support placement of Phacodinium
among the spirotrichs (Shin et al., 2000), these same 
gene sequences confirm the heterotrich affinities 
of Peritromus (Rosati, Modeo, Melai, Petroni, & 
Verni, 2004), Chattonidium , (Modeo et al., 2006), 
and Condylostomides (Schmidt, Foissner, Schlegel, 
& Bernhard, 2007). 
 In conclusion, we now recognize one order within 
the class, the Order Heterotrichida with characters of 
the class, and eight families: Family Blepharismidae 
[but see Aescht & Foissner, 1998], Family 
 Chattonidiidae Family Climacostomidae , Family 
 Condylostomatidae , Family Maristentoridae , 
Family Peritromidae , Family Spirostomidae , and 
Family Stentoridae (see Chapter 17. Ciliate Taxa ). 
6.1 Taxonomic Structure 131
132 6. Subphylum 1. POSTCILIODESMATOPHORA: Class 2. HETEROTRICHEA – Once Close to the Top
They are distinguished primarily by features of the 
oral region and variations in their overall body form. 
 A number of works have treated different genera 
in detail: Spirostomum (Repak & Isquith, 1974); 
Blepharisma (Repak, Isquith, & Nabel, 1977); 
Stentor (Foissner & Wölfl, 1994); and a recent 
report on the rare genus Copemetopus (Al-Rasheid, 
2001). We should not forget the classic works on 
Stentor , the majestic “king of the ciliates”, by Tartar 
(1961) and on Blepharisma , the light-sensitive pro-
tozoon by Giese and collaborators (1973). Hadži 
(1951) is the classic work on the folliculinids . 
 6.2 Life History and Ecology 
 Because of their typically large size, heterotrichs 
can be conspicuous members of microbial 
foodwebs and have a widespread distribution. 
 Heterotrichs have been recorded from freshwater 
lakes in subtropical Florida (Beaver & Crisman, 
1989b), Antarctica (Kepner, Wharton, & Coats, 
1999), Europe (Finlay, 1982), and high altitude 
lakes in South America (Woelfl & Geller, 2002), 
and streams in Europe (Madoni & Ghetti, 1980). 
They are found in a variety of marine habi-
tats, including anaerobic sediments in Europe 
(Fenchel & Finlay, 1990a), the marine sublittoral 
in Europe (Agamaliev, 1971; Azovsky & Mazei, 
2003; Kovaleva & Golemansky, 1979; Mazei & 
Burkovsky, 2003) and even deep marine habitats 
(Fenchel et al., 1995) and hydrothermal vents (Small 
& Gross, 1985; Bergquist et al., 2007). Heterotrichs 
are often dominant members of the low diversity 
ciliate communities of hypersaline habitats across 
the globe – in Europe (Esteban & Finlay, 2004), 
 Africa (Yasindi, Lynn, & Taylor, 2002), Arabia 
(Al-Rasheid, Nilsson, & Larsen, 2001; Elloumi 
et al., 2006), and Australia (Post, Borowitzka, 
Borowitzka, Mackay, & Moulton, 1983). They 
are occasionally found in soils (Buitkamp, 1977; 
Foissner, 1998a; Griffiths, 2002). 
 Most species are free-swimming, but some, 
such as Stentor , have the ability to use a holdfast 
to temporarily attach to the substrate (Fauré-
Fremiet, 1984). A few species of Stentor secrete 
a mucoid sheath and all species of folliculinids 
secrete a lorica in which they can retract to 
avoid predation. The substances for these external 
coverings originate from extrusomes (Bussers, 
1984; Mulisch & Hausmann, 1983), and in the 
 folliculinids may contain chitin fibrils (Mulisch, 
Herth, Zugenmaier, & Hausmann, 1983). Substrates 
to which heterotrichs attach include inorganic 
 substrates and macrophytes. Folliculinids attach to 
the integument of various invertebrates (Matthews, 
1968; Fernández-Leborans & Córdoba, 1997), 
and may cause the skeletal eroding band or brown 
band diseases of scleractinian corals (Antonius, 
1999; Cróquer et al., 2006). Maristentor is found 
on corals, but does not appear to cause disease 
(Lobban et al., 2002). 
 Some genera, like Fabrea , are strictly marine or 
brackish water forms, which can attain abundances 
of 10 5 l −1 (Elloumi et al., 2006; García & Niell, 
1993). Stentor species can reach more than 10 3 l −1 in 
some lakes in the southern hemisphere, perhaps due 
to the absence of larger microcrustacean predators 
(James, Burns, & Forsyth, 1995; Laybourn-Parry, 
Perriss, Seaton, & Rohozinski, 1997). Dispersal 
generally occurs by swimming, but cysts may also 
be involved (see below). Kusch (1998) has demon-
strated clear evidence of relatively high gene flow 
among populations of Stentor separated by as much 
as 400 km. Genera in the Family Folliculinidae 
are typically marine although the fresh-water 
 species Folliculina boltoni has been recorded from 
 Europe (Penard, 1919), North America (Hamilton, 
1952), and South America (Dioni, 1972) while 
Ascobius lentus has been recorded recently in 
European freshwaters (Mulisch, Heep, Sturm, & 
Borcherding, 1998). Folliculinids are dispersed in 
part by the movements of their host, but the proter 
or anterior daughter differentiates at cell division 
as a “mouthless swarmer ” stage that is adapted for 
 Heterotrichs are omnivorous, upstream filter feed-
ers (Fenchel, 1980a), showing little preference for 
prey species. Bacteria , autotrophic and heterotrophic 
 flagellates , and ciliates are ingested, with some 
prey species proving more nutritious than others 
(Rapport, Berger, & Reid, 1972; Repak, 1983, 1986). 
Heterotrichs may change the shape of the oral region 
(Liebsch, 1976) and the spacing between the cilia 
of the oral polykinetids (Rickards & Lynn, 1985) 
in response to physiological states and prey types. 
When smaller food items become scarce, heterot-
richs can become cannibalistic (Foissner & Wölfl, 
1994; Giese, 1973; Pierce, Isquith, & Repak, 1978) 
and have also been known to ingest smaller metazoans 
(Foissner & Wölfl; Tartar, 1961). In an unusual 
turn of the tables, it appears that Mirofolliculina 
limnoriae , an epibiont on the wood-boring isopods 
of the genus Limnoria , may outcompete its host for 
food and hinder host dispersal, suggesting it can be 
considered an ectoparasite (Delgery, Cragg, Busch, 
& Morgan, 2006). 
 Heterotrichs harbor a variety of endosymbionts : 
 bacteria can be found in the cytoplasm and in 
the macronucleus (Fokin, Schweikert, Brummer, & 
Görtz, 2005; Görtz, 1983; Görtz & Wiemann, 1987). 
The bacterial endosymbionts do not appear to be 
harmful; in fact, some bacteria may be essential sym-
bionts (Hufschmid, 1984). A variety of Chlorella spe-
cies provide their Stentor and Climacostomum hosts 
with the “by-products” of photosynthesis (Fernández-
Leborans & Zaldumbide, 1983; Kawakami, 1984; 
Reisser, 1984; Woelfl & Geller, 2002), and may com-
pete with bacterial endosymbionts for the host cyto-
plasmic niche (Hufschmid, 1984). Laybourn-Parry et 
al. (1997) determined that Stentor amethystinus could 
contribute almost 70% of the total plankton photosyn-
thesis in some Australian lakes. 
 Heterotrichs themselves are prey for other ciliates 
and metazoans. Stentor has mechanoreceptors dis-
tributed on its cell surface that may enable response 
to predator contact (Wood, 1989). When contact is 
made with toxicyst-bearing litostome ciliates, like 
Dileptus (see Chapter 9 ), Blepharisma (Harumoto 
et al., 1998; Miyake, Harumoto, Salvi, & Rivola, 
1990), Climacostomum (Masaki et al., 1999), and 
Stentor (Miyake, Harumoto, & Iio, 2001) induce a 
massive release of their pigmentocysts , respectively 
containing the pigments blepharismin , climacostol , 
and stentorin , which have proved lethal to this 
predator. However, the pigment does not inhibit 
predation by the heterotrich Climacostomum on 
its heterotrich relative Blepharisma (Terazima & 
Harumoto, 2004). 
 Pigmented heterotrichs also exhibit light-sensitive 
behavior (Giese, 1973). Their photophobic response 
appears as a ciliary