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sidered without the prefix; many structures and 
organelles that are (micro)fibrillar in composition 
are composed of non-hollow filaments 4–10 nm 
in diameter; the term is most frequently used in its 
adjectival form; fibrillar or microfibrillar constituents 
may include such prominent and organized structures 
as the kinetodesma , myoneme , and spasmoneme , and 
perhaps the karyophore and the filamentous annu-
lus ; “filamentous” may be used to describe the very 
same organelles; see Microfilament . 
Microfilament : generalized term, perhaps better 
considered without the prefix; the finer or finest 
composition ( ca . 5 nm in diameter) of a number of 
important organelles appears to be microfilamen-
tous in nature, often densely so and with or without 
nodes; microfilamentous structures may include 
the epiplasm , the filamentous reticulum , and the 
infraciliary lattice ; if this is the ultimate or lowest 
macromolecular level of organization, then there 
should be a distinction, even in very generalized 
usage, between this term and microfibrils , but this 
has not always been the case in the literature – the 
terms have been used interchangeably by some 
workers; see Microfibril . 
Microgament : see Gamont . 
Micronucleus (pl. Micronuclei ): so-called gen-
erative nucleus, typically much smaller than the 
macronucleus ; may be multiple, generally spheri-
cal or ovoid in shape, and typically diploid in its 
genomic content; without nucleoli and typically 
showing no transcriptional activity; its nuclear
envelope with pores in some species, without them 
in others; divides mitotically or meiotically, play-
ing a major role in sexual phenomena, such as 
autogamy and conjugation ; absent in amicronucleate
strains or races (Mi, Figs. 2.9Af, 2.12). 
Microphagous : feeding on small or very small 
particles of food; a generalized term embracing 
especially bacterivorous and sometimes algivorous
feeding; to be contrasted with carnivorous, histopha-
gous, saprozoic, and especially macrophagous . 
Micropyle : differentiated pore in the wall of a 
resting cyst through which the ciliate emerges on 
excystment; the pore canal is sealed by cyst wall 
material; found in some spirotrichs and colpodeans 
(Mpy, Fig. 2.9Ag). 
Microstome : a stage in the polymorphic life cycle in 
which the oral apparatus undergoes morphogenesis 
to become reduced in size and capable of ingesting 
only small prey items, typically bacteria; see 
Macrostome (Fig. 2.4A). 
38 2. Glossary of Terms and Concepts Useful in Ciliate Systematics
Microstome-Macrostome Transformation : see 
Stomatogenesis . 
Microtoxicyst : used as a synonym of haptocyst , 
but might also refer to some other minute toxicyst . 
Microtubular Ribbons : a set of microtubules
aligned laterally to form a flat “ribbon-like” struc-
ture; the most striking microtubular ribbons include 
the transverse and postciliary microtubules , and 
the microtubular arrays in the suctorial tentacle
(Figs. 2.1, 2.2, 2.10). 
Microtubule : hollow, cylindrical structure of 
indeterminate length, ca . 20–25 nm in diameter, 
composed of subunits of tubulin ; rigid, often cross-
linked with others to form a microtubular ribbon
or nematodesma ; microtubules in the cytoplasm 
are typically associated with the kinetosome (Figs. 
2.1, 2.2, 2.10). 
Microzooid : see Zooid . 
Migratory Form : see Larval Form . 
Missile-like Body : see Haptocyst . 
Mitochondrion (pl. Mitochondria ): generally con-
spicuous organelles in the cytoplasm, composed 
of a complex membrane system with the inner 
membrane appearing to form cristae of several 
types, usually tubular in ciliates, and indispensably 
functioning as the “powerhouse” of the cell; in some 
ciliates, arranged in specific (often linear) patterns or 
formations; in scuticociliates , apparently fused (?) in 
a single interconnected “compound” mitochondrion, 
a giant chondriome located immediately under the 
pellicular alveoli; in some ciliates, independently 
transformed to a hydrogenosome (e.g., armophor-
eans , litostomes , plagiopyleans ). 
Mixokinetal : stomatogenesis in which both paren-
tal somatic kineties and parental oral structures
are simultaneously involved in development of 
the opisthe’s oral anlage ; found in nassophoreans , 
 apostomes , and the spirotrich Protocruzia . 
Mixotrophic : capable of using two or more modes 
of nutrition (e.g., autotrophic and heterotrophic ). 
Monogemmic : production of a single bud (at a time);
a mode of fission . 
Monokinetid : a kinetid composed of one kineto-
some and its fibrillar associates; see Dikinetid , 
Dyad , and Polykinetid (Figs. 2.1E, 2.2). 
Monoparakinetal : parakinetal stomatogenesis in 
which only one somatic kinety is involved in for-
mation of the oral anlage ; found in tetrahymenids 
(Fig. 2.11Dd). 
Monophyletic : condition of a taxon being com-
prised of a common ancestor and descendants all 
presumed to be derived from this common ances-
tor; established by the cladistic approach through 
the sharing of apomorphic or derived characters ; 
see Clade , Paraphyletic , and Polyphyletic . 
Monostomy : condition of having but one cytostome . 
Monotelokinetal : telokinetal stomatogenesis in 
which the oral anlage is derived by proliferation of 
kinetosomes in the somatic portion of oral kineties ; 
found in pleurostome haptorians . 
Monotomic : division of a single individual into 
but two filial products ; the mode of fission typical 
of most ciliates. 
Monotypic : a taxonomic group having only one 
included nominal taxon; for example, a monotypic 
genus includes only one species. 
Monoxenic Culture : literally “one stranger” culture; 
laboratory growth of two kinds or species of living 
organisms with no others present; for example, 
a ciliate plus one “stranger” − a bacterium, an alga, a 
yeast, or another ciliate species; the second organism is 
typically present in the medium to serve as food for 
the ciliate of interest, which is usually being studied 
biochemically or ecologically. 
Morphogenesis : coming-into-being of characteristic
and specific form; the transformation involved in 
growth and differentiation or ontogeny , resulting 
in reproduction of the preexisting form, with the 
same patterned array of cytoarchitectural substruc-
tures; morphogenetic movements are involved in 
the process of fission , but also in cystation , conju-
gation , regeneration , and particularly in stomato-
genesis ; the consistent patterns of such dynamic 
ontogenetic phenomena may be of considerable 
value in both phylogenetic and comparative taxo-
nomic work; see also Biogenetic Law . 
Morphological Species : an assemblage of popula-
tions of organisms that share a strong and stable 
morphological similarity; often assumed by taxono-
mists to represent a biological species , but likely to 
represent a number of different biological entities. 
Glossary 39
Morphospecies : see Morphological Species . 
Motorium : see Neuromotorium . 
Mouth : of value only as a very general term, used 
in reference to the oral region of any mouth-bearing
ciliate; the “true” mouth of a ciliate should be 
called the cytostome . 
Mucigenic Body : see Mucocyst . 
Mucocyst : cortical, membrane-bound, saccular or 
rod-shaped extrusome with a paracrystalline struc-
ture; dischargeable as an amorphous, mucus-like 
mass through an opening in the pellicle; probably 
involved in cyst formation, among other possible 
functions; occurs in regular, longitudinal, interki-
netal rows in many ciliates; formerly known as a 
protrichocyst (especially), a mucous trichocyst, or 
a mucigenic body; an ampullocyst has been consid-
ered a special type of mucocyst (Fig. 2.9Cb). 
Mucous Trichocyst : not a trichocyst ; see 
Mucocyst . 
Müller’s Vesicle : small vacuole containing mineral 
concretions, and functioning as a gravity receptor; 
found in karyorelicteans