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such as Loxodes . Mutualism : kind of symbiotic relationship in which both partners benefit from the association, the host as well as the ecto - or endosymbiont ; veri- fiable cases rare in which ciliates are the symbiont, but there are several in which the ciliate is the host (e.g., Omikron in Euplotes ; zoochlorellae of Paramecium ). Myoneme : fibrillar, ultimately filamentous, organelle with a known or presumed contractile function; in the broadest sense, may include the spasmoneme found in the stalk of many peritrichs, the M-bands or M fibers coursing beneath or beside the kineties in the bodies of certain contractile heterotrichs , retrac- tors and sphincters in various other groups, and still additional (micro)filamentous strands, bands, sheets or bundles active in contraction or retraction of all or part of a ciliate\u2019s body; the fibrils, sometimes running deep in the cytoplasm, may be interconnected to one another, the pellicle, and/or certain kinetosomes . N Naked : see Barren Kinetosome . Nasse : see Cyrtos . Nebenkörper : literally \u201cneighboring body\u201d and used variously in protozoology; in the case of ciliates, it has been applied, formerly but now inappropri- ately, to the parasomal sac , which is so often found in the near vicinity of kinetosomes. Neck : term used variously; the often highly exten- sible region of the body that is immediately pos- terior to the apical cytostome and corona in some haptorians ; the non-extensible, sometimes quite elongate, part beneath the flared apical end of chonotrichs, but better called a collar . Nematocyst : not a preferred term; see Ortho- nematocyst . Nematodesma (pl. Nematodesmata ): birefringent bundle of parallel microtubules , often showing a hexagonal, paracrystalline arrangement in cross- section; typically, kinetosome -associated; plunging into the cytoplasm at right angles to the pellicle, forming with others the major reinforcements of the cytopharyngeal apparatus ( rhabdos and cyrtos ) of haptorians , nassophoreans , and cyrtophorines , but also found in other groups (e.g., in frontoniids); formerly identified with light microscopy as tri- chites, cytopharyngeal rods, or the cytopharyngeal basket (Nd, Figs. 2.5B, 2.7j). Neoformation Organelle : a permanent tube-like invagination of the cell surface in which the oral struc- tures of some oligotrichs (e.g., Pelagostrombidium ) develop; see Intracytoplasmic Pouch . Neoteny : retention of major larval characters in the mature or adult form ; the trophont of mobiline peritrichs is sometimes considered a matured or permanently arrested telotroch (i.e., the larval form in sessiline peritrichs). Neotype : single specimen designated as the name- bearing type of a species; established when it is believed that no holotype , lectotype or syntype(s) exist. Nephridial Apparatus : see Contractile Vacuole . Nephridial Canal : see Afferent Canal . Nephridioplasm : see Spongioplasm . Neritic : pertaining to the region of shallow water along a seacoast; the biotope near the shoreline edge of an ocean; to be contrasted with pelagic . Nesselkapseltrichocyste : see Toxicyst . 40 2. Glossary of Terms and Concepts Useful in Ciliate Systematics Neuroformative System : see Neuromotorium . Neuromotor Apparatus : see Neuromotorium . Neuromotor Concept : see Neuromotorium . Neuromotorium : presumed center or cytobrain or motorium of a ciliate\u2019s entire neuromotor apparatus (associated with the now discarded but once very popular Neuromotor Concept); a chromophilic fibrillar bundle formerly thought to play a con- ductive or active coordinating role in locomotion, feeding, avoidance, and other behaviours; identi- fied as the rest of the \u201cneural\u201d apparatus were various parts of the argyrome and/or structures today known to be microtubular or microfibrillar organelles of diverse sorts. Nomen Conservandum : name to be conserved; with appropriate permission, a name preserved as an exception to some provision of the International Code of Zoological Nomenclature . Nomen Dubium : dubious or doubtful name; a name of uncertain application through lack of suffi- cient information about it or the organism or taxon with which it might be associated. Nomen Novum : new name; a name expressly proposed and published as replacement of another name, usually a junior homonym requiring such action; often abbreviated to \u201cnom. nov.\u201d Nomen Nudum : \u201cnaked\u201d name; a name published without description of its associated taxon; a diag- nosis is necessary to validate both the name and taxon involved. Nomen Oblitum : forgotten name; a name unused as a senior synonym for more than 50 years; a long unused invalid name often literally \u201cforgotten\u201d by taxonomists of the group and generally best left in that condition. Nonciliferous Kinetosome : see Barren Kinetosome . Nonhomologous : the exact opposite of a homolo- gous character ; however, either character may have an analogous function with some other structure. Nuclear Dualism : presence or existence of two different kinds of nuclei; for example, the micro - and macronucleus so characteristic of the great majority of ciliates; exhibition of the heterokaryo- tic condition (Fig. 2.12). Nuclear Envelope : system of membranes or cov- erings of a nucleus; composed of two unit mem- branes , typically continuous with the endoplasmic reticulum and often replete with minute pores. Nuclear Membrane : older term for nuclear enve- lope . Nucleolus (pl. Nucleoli ): typically visible region of the nucleus where assembly of ribosomes is organized around the ribosomal RNA genes; see Endosome (Nuc, Fig. 2.12g, 2.12i). Nucleus (pl. Nuclei ): see Macronucleus and Micronucleus . Numbering Conventions : (1) Kineties are num- bered \u2013 following the method of Chatton and Lwoff \u2013 around the body clockwise when viewed from the apical pole, with Kinety Number 1 , for example, being the rightmost postoral meridian , which, in certain hymenostomes , also bears the cytoproct posteriorly and is normally the stoma- togenic kinety ; no matter the total number, the last one, immediately to the viewer\u2019s right of Kinety Number 1 , is conventionally labelled as \u201cn\u201d (Fig. 2.7a, 2.7b, 2.7e). For counting kineties, the method of von Gelei, but subsequently generally ignored, gives results exactly the opposite from those of the Chatton and Lwoff system: Number 1 is the same, but the suggested direction of count- ing is counter-clockwise, and thus the Number \u201cn\u201d meridian is on the right rather than the left side of the first kinety. (2) Microtubular triplets of a kinetosome are num- bered \u2013 following the convention of Grain (1969) \u2013 clockwise around the proximal end of the basal body, viewed as in cross-section from the inside of the organism looking out, with Number 1 being the triplet lying in the axis of the kinety, but it is often less ambiguous to make use of the location of the postciliary microtubules , which are assumed to be associated with Number 9, the last triplet (Fig. 2.1D). For counting kinetosomal triplets, the convention of Pitelka (1969) considers Numbers 1\u20133 to be on the right anterior margin of the kinetosome, looking at a cross-section from the base outward, and associated with the kine- todesma (of Paramecium ); the counting similarly proceeds clockwise around the base. In the Pitelka convention, the triplet associated with the postcili- ary microtubular ribbon is always number 5. This Glossary 41 equals Number 9 of the Grain convention, the system adopted in this book (Fig. 2.1D). O Occam\u2019s Razor : equivalent to the principle of parsimony, viz ., when faced with two or more hypotheses of equally explanatory value, choose the simplest. Ogival Field : transitory group of kinetosomes, bear- ing thigmotactic cilia , which appear