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: nominal species designated as the 
type of a genus-group taxon; it cannot be removed 
from that genus. 
Type-specimen : single specimen (perhaps whole 
slide of cloned organisms will be acceptable for 
protozoological materials in the future) known as 
the type or type-material of a taxon in the species-
group; major kinds include the holotype (first 
specimen and more important), lectotype (named 
later from the type series if no holotype exists), and 
neotype (if all other type material lost); paratypes 
and syntypes are the extra specimens in a series 
from which a holotype or lectotype has been cho-
sen (refer to the International Code of Zoological 
Nomenclature for detailed definitions). 
Ubiquitous : the worldwide dispersal of individuals 
of a species. 
Undulating Membrane : an older term for the oral 
ciliature on the right side of the oral cavity , implying 
a function that is not always realized, whereas paroral
refers solely to the structure’s location; also widely 
used for a different structure in certain flagellate proto-
zoa; made popular as the UM of the tetrahymenines 
in which its presence is so neatly revealed by silver-
impregnation techniques , its base – on the right side 
of the buccal cavity – standing in bold contrast to the 
three membranelles on the left side; see Paroral and 
Tetrahymenal Buccal Apparatus . 
Undulipodium (pl. Undulipodia ): see Cilium . 
Unit Membrane : the phospholipid-protein layer 
that appears as a trilaminar structure in transmis-
sion electron microscopy; it delimits the bounda-
ries of the cell (i.e. plasma membrane ) and of 
many organelles (e.g. mitochondria, nucleus, 
vesicles ). 
Unit Organelle : subcellular structure (e.g., cilium, 
kinetosome, food vacuole) that is directly involved 
in subsidiary cell functions and that is composed 
of specific aggregations of macromolecules, often 
themselves morphologically recognizable as subor-
ganelles (e.g., microtubules). 
Vacuole : generalized term used for all sorts of siz-
able, fluid-filled, unit membrane -bound cavities or 
sacs in the cytoplasm (e.g., concrement vacuole , 
contractile vacuole , food vacuole ); compare with 
Vesicles . 
Variety : used as a synonym for the preferred term 
syngen ; also, in a second and inaccurate mean-
ing, considered as a formal taxonomic rank at an 
infraspecific level; but, along with forma, which 
is used by specialists of some groups, such as the 
 entodiniomorphids , should not be so used in cili-
atology; culture, deme , ecophenotype, population, 
stock , strain , and race are preferable terms. 
Vegetative Nucleus : see Macronucleus . 
Vegetative Reproduction : synonym for asexual
reproduction or binary fission . 
Veloid : see Velum . 
Velum : variously used for the paroral membrane 
of some scuticociliates , sometimes termed a veloid; 
the extensor membrane of peritrichs ; the flange ; the 
skirt-like pellicular fold covering the marginal cilia
in mobiline peritrichs . 
60 2. Glossary of Terms and Concepts Useful in Ciliate Systematics
Ventralization : presumed evolutionary process 
whereby the oral region comes to be located on the 
anterior ventral surface rather than in a wholly apical 
or near-apical position; position of cytostome funda-
mentally ventral, with no shift during fission. 
Vesicle : unit membrane -bound cavity or sac in the 
cytoplasm of a size usually much less than that of 
a typical vacuole (e.g., discoidal vesicles , parts of 
the Golgi apparatus and endoplasmic reticulum , 
the pellicular alveolus , and pinocytotic vesicle); 
water expulsion “vesicle” is a misnomer for the 
contractile vacuole . 
Vestibular Ciliature : rows or files of oral cilia
only slightly modified from and sometimes only 
extensions of somatic kineties; characteristically 
located in a cavity or depression, the vestibulum ; 
vestibular kinetids may have cilia longer or closer 
together, and may show minor differences in the 
organization of the kinetids compared to kinetids 
of the somatic region ; compare to Ophryokinety
and Prebuccal Ciliature . 
Vestibular Kinety (pl. Kineties ) : see Vestibular 
Ciliature . 
Vestibule : see Vestibulum . 
Vestibulum (pl. Vestibula ): a ciliated depression 
or invaginated oral region , at either pole, leading 
directly or indirectly to the oral cavity and adorned 
with vestibular ciliature. 
Vestige : a visible trace or part of a structure or 
organelle persisting, usually as a nonfunctional 
remnant, in one stage (typically the mature adult
form ) as a carry-over from an earlier ontogenetic 
stage in which it was fully developed and func-
tional; curiously enough, the remnant or vestige of 
an ontogenetic structure may serve as the anlage
for production of that same structure in the next 
(repeated) stage in the life cycle (e.g., the scutico-
vestige in the mature form of some scuticociliates 
is apparently a major source of the kinetosomes 
forming the anlage for the scutica proper); see also 
Erratic Kinetosomes . 
Vierermembran : see Quadrulus . 
Vierteilige Membran : see Quadrulus . 
Watchglass Organelle : see Lieberkühn, 
Organelle of . 
Water Expulsion Vesicle : see Contractile Vacuole . 
Xenodeme : see mention under Deme . 
Xenosomes : literally “alien bodies”; a bacterial 
endosymbiont in the cytoplasm of certain marine 
 scuticociliates (e.g., Parauronema ); see also 
Endosymbiont ( of Ciliates ). 
Xeric : pertaining to a terrestrial habitat having a 
very low content of water (e.g., desert sands). 
Xylophagous : literally “wood-eating”; capable of 
digesting cellulose, such as certain trichostomes 
and entodiniomorphids in the digestive tract of 
various mammalian herbivores. 
Zeta Membranoid : see Membranoid , 
Haplokinety , and Paroral . 
Zone of Stripe Contrast : see Locus of Stripe 
Zoochlorella (pl. Zoochlorellae ): endosymbiotic 
green algae, typically chlorophytes, found widely 
in the cytoplasm of ciliates belonging to nearly all 
major taxa; see Endosymbiont ( of Ciliates ). 
Zooid : generally restricted to mean only the 
body proper of an attached sessile form (e.g., 
the bell of many peritrichs ), minus the stalk ; the 
individual members of a free or attached colony, 
but usually only of the arboroid colony so typical 
of peritrichs ; macrozooids and microzooids are 
distinguishable by size and exhibition of certain 
functional differences (e.g., only macrozooids of 
Zoothamnium are capable of starting new colo-
nies) (Z, Fig. 2.8Bb, 2.8Bc). 
Zooplankton : see Plankton . 
Zoopurpurin : see Blepharismin . 
Glossary 61
Zooxanthella (pl. Zooxanthellae ): endosymbiotic 
“non-green” algae, typically mutualistic dinoflag-
ellates , cryptomonads or chrysomonads , found in 
the cytoplasm of ciliates; see Endosymbiont (of
Ciliates) . 
Zweigliedrige Kultur : see Monoxenic Culture . 
Zygopalintomy : see Syndesmogamy . 
Zygotic Nucleus (pl. Nuclei ): fusion product of 
two gametic nuclei ; see Synkaryon . 
Fig. 2.1. Kineties and kinetosomes of the somatic cortex. A Structure of somatic kineties. a . Somatic kineties are files 
of kinetosomes (Ks) linked by kinetodesmata (Kd), which appear on the left side of the kinety, if viewed from the out-
side ( a , bold) or top ( b ) and bottom ( c ), and on the right side of the kinety, if viewed from the inside ( a , not bold). B
Detailed structure of a single kinetosome (Ks) and its cilium at five different levels ( a , b , c , d , e ). The axoneme (Axn) 
is composed of 9 peripheral doublets in the cilium ( a–d ) that transform to triplets in the kinetosome ( e ). The central 
pair of ciliary microtubules arise from the axosome (Axs). A parasomal sac (PS) is adjacent to the cilium, which is 
surrounded by pellicular alveoli (PA) underlying the plasma membrane. The kinetosome, viewed from the inside
Fig. 2.2. Schematic

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