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Cap 17

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pressed, smooth in outline except for two promi-
nent anterior spines and one posterior spine ; 
free-swimming; somatic ciliature, sparse and frag-
mented into several cirrus-like clusters posteriorly; 
a preoral band of cilia on a conspicuous trans-
verse ridge anterior to the oral cavity ; oral cavity 
in posterior half with several oral polykinetids and 
a paroral; macronucleus, globular; micronucleus 
(?); contractile vacuole, present; cytoproct (?); 
feeding (?); in freshwater anaerobic habitats; one 
 – Discomorphella Corliss, 1960 
 Family EPALXELLIDAE Corliss, 1960 
 (for Epalcidae and Epalxidae ) 
 Size, small; shape, box-like, generally with short 
posterior spines, and some species with well-devel-
oped spine overhanging hidden oral cavity; free-
swimming; somatic ciliature, relatively dense in 
its short anterior and posterior linear kinetof-
ragments, with those at the anterior end parallel 
to and anterior of the oral opening on both left 
and right sides of the body ; oral cavity, roughly 
equatorial, with several oral polykinetids; paroral, 
may be absent; macronucleus, globular to ellipsoid; 
micronucleus, present; contractile vacuole, present; 
cytoproct (?); feeding (?); in marine and freshwa-
ter anaerobic habitats, principally freshwater, but 
a few Epalxella species also in marine biotopes; 
three genera. 
 – Epalxella Corliss, 1960 
 – Pelodinium Lauterborn, 1908 
 – Saprodinium Lauterborn, 1908 
 Family MYLESTOMATIDAE Kahl in Doflein & 
Reichenow, 1929 
 (syns. Atopodiniidae , Mylestomidae ) 
 Size, small; shape, discoid; free-swimming; 
somatic ciliation very sparse, with anterior 
kinetofragments restricted to the ventral (= oral) 
surface, extending only slightly onto the left and 
right surface, and with longer cilia at posterior, 
17.3 The Ciliate Taxa to Genus 411
cirrus-like in Myelostoma ; oral cavity, in posterior 
half, with several oral polykinetids; paroral, may 
be absent; macronucleus, globular to ellipsoid; 
micronucleus, present; contractile vacuole, present; 
cytoproct (?); feeding (?); in marine and freshwater 
anaerobic habitats, predominantly in freshwater but 
a few Mylestoma species are marine; two genera. 
 – Atopodinium Kahl, 1932 
 – Mylestoma Kahl, 1928 
et al., 1974 
 (syns. Aspirigera p.p ., Aspirotricha p.p ., Cyrtostomata 
p.p ., Holotricha [ Holotrichasina , Holotrichia ] p.p ., 
 Homoiotricha p.p ., Kinetodesmatophora p.p ., 
 Membranellophora [ Membranellata ] p.p ., Stomatea 
p.p ., Axotrichidea + Peritrichidea ; Hymenotricha 
(sensu Raabe) + Peritricha; Tetrahymenophora + 
 Cyclohymenophora ) 
 Size, small to medium, rarely large; shape, typi-
cally ovoid to elongate ovoid; free-swimming, but 
sessile and sedentary in Subclass Peritrichia ; alve-
oli, well-developed; somatic ciliation, holotrichous; 
somatic monokinetids with anteriorly directed, dis-
tinct, overlapping kinetodesmal fibrils, divergent 
postciliary ribbons, and radial transverse ribbons 
(except in Subclass Peniculia , which has tangential 
transverse ribbons); posterior kinetosome of somatic 
dikinetids similar to that of a monokinetid unit 
while anterior kinetosome bears only a tangential 
transverse ribbon; parasomal sacs, typically to left 
or anterior of kinetosomes; somatic extrusomes as 
mucocysts, but trichocysts common in Subclass 
 Peniculia in which mucocysts are rare; oral appara-
tus with a distinct right paroral of dikinetids (i.e. 
stichodyad) and typically three left oral polyki-
netids, but oral apparatus absent in Subclass
Astomatia, and highly modified in the Subclass
Apostomatia ; stomatogenesis varies with subclass, 
of buccokinetal or parakinetal types; division while 
free-swimming, but typically in cyst in parasitic 
forms; macronucleus, homomerous, typically sin-
gle; micronucleus, one to many; conjugation, usu-
ally temporary, but total in Subclass Peritrichia ; 
cytoproct, typically located in the director meridian; 
feeding on bacteria and microalgae, but occasionally 
carnivorous in larger forms with the endocommensal 
 astomes entirely osmotrophic; in marine, freshwa-
ter, and terrestrial habitats, distributed widely as 
free-living forms with many species of the Subclass 
 Peritrichia as symphorionts and the entire Subclass 
 Astomatia endocommensalistic; six subclasses. 
 Subclass Peniculia Fauré-Fremiet in Corliss, 1956 
 (syns. Trichohymenostomata and Vestibulata sensu
von Gelei) 
 Size, medium; shape, ovoid; free-swimming; 
alveoli, well-developed; somatic ciliation, holotri-
chous, typically dense, with distinct pre- and post-
oral sutures, but Order Urocentrida with girdle-like 
ciliature; caudal cilia, often conspicuous; somatic
kinetids with tangential, not radial, transverse 
ribbons, but other fibrillar associates as for class ; 
somatic extrusomes as trichocysts, but mucocysts 
in Order Urocentrida ; oral structures, typically 
three left oral polykinetids with the long axis of 
the polykinetid (peniculus) parallel to the long 
axis of the oral cavity, and with alveoli between 
kinetosomal rows of oral polykinetids ; paroral, 
reduced, but present throughout interphase; no 
cyrtos, but nematodesmata may be associated with 
oral and perioral kinetosomes, sometimes loosely 
basket-like; stomatogenesis, ophryobuccoki-
netal ; many species with endosymbiotic algae or 
bacteria; microphagous bacterivores, algivores, and 
some species carnivorous (e.g. Neobursaridium ); 
cysts, rare; distributed widely, predominantly in 
freshwater habitats, but some marine species; two 
NOTE : Lynn and Small (2002) presented a 
single Order Peniculida divided into the Suborders 
 Frontoniina and Parameciina . However, small sub-
unit rRNA gene sequences do not strongly support 
this subdivision (Fokin, Andreoli, Verni, & Petroni, 
2006; Strüder-Kypke, Wright, Fokin, & Lynn, 
2000b), but do provide support, corroborated by 
morphology, for separation of the urocentrids at a 
higher level (Didier & de Puytorac, 1994). 
 Order Peniculida Fauré-Fremiet in Corliss, 1956 
 (syns. Frontoniina ; Frontoniina + Quadrulina p.p .; 
 Lembadionina , Parameciina , Peniculina ) 
 Size, small to large; somatic ciliation, holotri-
chous; somatic kinetids, predominantly dikinetids; 
somatic extrusomes as trichocysts ; seven families. 
412 17. The Ciliate Taxa Including Families and Genera
 (syn. Clathrostomidae ) 
 Size, medium; shape, ovoid; free-swimming; 
somatic ciliation, holotrichous, with preoral and 
postoral sutures; ophryokineties, absent; oral region 
in anterior 1/4 of body; oral apparatus with six 
oral polykinetids, each one a file of dikinetids; 
oral nematodesmata, forming a ring around 
cytopharynx ; macronucleus, elongated ellipsoid; 
micronucleus, present; contractile vacuole, present; 
cytoproct, present; feeding on bacteria and micro-
algae; in freshwater habitats; one genus. 
 – Clathrostoma Penard, 1922 
 Family FRONTONIIDAE Kahl, 1926 
 (for Chiliferidae ) 
 Size, medium to large; shape, ovoid to bluntly 
ovoid; free-swimming; somatic ciliation, holotri-
chous, with postoral suture only; ophryokineties, 
often many, to right of oral region ; oral region, 
subapical, elongate in anterior 1/2–1/3 of body; 
prebuccal area, shallow or absent ; oral appa-
ratus, typically three long, large polykinetids in 
oral cavity with the paroral along its right border; 
cytostome expansible along postoral suture ; 
oral nematodesmata not forming a ring around 
the cytopharynx, but more prominent to its side 
and posterior; macronucleus, ellipsoid to elongate 
ellipsoid, sometimes band-form; micronucleus, 
present; contractile vacuole, single; cytoproct, 
present; often containing zoochlorellae; feeding 
on bacteria and microalgae; in marine, freshwater, 
and terrestrial habitats, typically free-living but 
one species commensal (?) on gills

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