Ultrastructure of Prorodon (Ciliophora, Prostomatida) I. Somatic Cortex and Some Implications Concerning Kinetid Evolution In Prostomatid and Colpodid Ciliates

ABSTRACT. This study describes the ultrastructure of the somatic cortex of Prorodon aklitolophon and Prorodon teres. the meridionally arranged somatic kineties of both species can be separated into two parts: a short anterior part, which consists of a few somatic dikinetids (in which both kinetosomes are ciliated), and a longer posterior consisting of monokinetids. the somatic monokinetids are associated with a convergent postciliary microtubular ribbon, a transverse microtubular ribbon flatly inserted in front of the kinetosome, a short and steeply extending kinetodesmal fibre attached to kinetosomal triplet 5 and 7, and a desmose anterior to triplet 3. From this desmose, two to five prekinetosomal microtubules originate and extend anteriorly. the posterior kinetosome of the somatic dikinetids is associated with the same microfibrillar and microtubular structures as the somatic monokinetid, except that no prekinetosomal microtubules originate from the desmose. the anterior kinetosome has a single postciliary microtubule and a tangentially oriented transverse microtubular ribbon. the permanent collecting canals of the unique contractile vacuole system extend parallel and adjacent to the somatic kinetics of Prorodon . the collecting canals are supported by the prekinetosomal microtubules. A similarly organized contractile vacuole system is not yet known from any other ciliate group. One of the most surprising results of this investigation was finding a significant similarity between the somatic dikinetid pattern of Prorodon and the colpodid dikinetid pattern. A hypothesis is presented to illustrate the evolution of the somatic kinetid patterns in colpodid and prostomatid ciliates.     

Somatic Infraciliature in the Haptorid Ciliate Homalozoon vermiculare (Kinetophragminophora, Gymnostomata) Ditransversalia N. Subcl. and Phylogenetic Implications

The ultrastructure of the cortex of Homalozoon vermiculare is described. The ventral side bears 13–15 iongitudinal kineties composed of monokinetids. On the dorsal surface, there are 3 kineties, 2 of which are composed of dikinetids in the anteriormost part of the cell. Consequently there exist 3 different kinds of kinetids within the somatic cortex: 1) The monokinetids on the ventral side are associated with a kinctodesmal fibril, 2 transverse microtubular ribbons and 7 postciliary microtubules in a double-row configuration; 2) The monokinetids on the dorsal side are very similar but they are associated with just 3 very 'short postciliary microtubules; 3) The posterior kinetosome of the dorsal dikinetids bears the same fibrillar associates as the dorsal monokinetid, but it lacks the second transverse ribbon. The anterior kinetosome of each pair is associated with a single postciliary' microtubule. The kinetid organization of Homalozoon is compared to that of other members of the Haptorida. Their phylogeny is discussed. A monophyleiic taxon within the litostomate ciliates is characterized by data on the somatic kinetids, and the new subclass Ditransversalia n. subcl. is constituted. The new subclass comprises the genera Balantidium, Bryophyllum, Enchelydium, Homalozoon, Isotricha, Lacrymaria, Lepidolrachelophyllum, Spathidium and Vestibulongum .     

Ultrastructure of Prorodon (Ciliophora, Prostomatida) Ii. Oral Cortex and Phylogenetic Conclusions

ABSTRACT. The ultrastructure of the oral region and the ultrastructural architecture of the basket of Prorodon aklitolophon and Prorodon teres are described. the oral region of Prorodon consists of: 1) A circumoral kinety at the anterior pole of the cell surrounding the typically slit-shaped cytostomial funnel. This kinety is composed of inversely oriented dikinetids in which both kinetosomes are ciliated and are associated with a very short postciliary microtubular ribbon and a few transverse microtubules; 2) Three brush rows aligned in parallel and extended meridionally in the anterior part of the cell. the individual brush rows consist of dikinetids, but in contrast to the dikinetids around the cytopharynx they are not inverted and only the anterior kinetosomes bear specialized short brush cilia and are associated with a divergent-tangential transverse microtubular ribbon. the posterior kinetosome is non-ciliated and bears a prominent convergent postciliary microtubular ribbon. Schematized dikinetid patterns of both oral regions of Prorodon are provided. In addition, a three-dimensional reconstruction of the basket of the genus Prorodon based on serial thin sections is presented. A phylogenetic tree, mainly based on stomatogenic data, is given to show the phylogenetic relationships of some prostomatid genera as well as the hypothesized sistergroup relationship of colpodid and prostomatid ciliates.     

Cortical ultrastructure of Coleps bicuspis Noland, 1925 and the phylogeny of the class Prostomatea (Ciliophora)

The ultrastructure of Coleps bicuspis Noland, 1925 is described. The ciliate is a typical prostomate: the somatic kinetid is a monokinetid with a postciliary ribbon at triple 9, a kinetodesmal fibril originating near triplets 5, 6, 7 and an apparently radial transverse ribbon at triplet 4. The oral area is circular and has three brosse kineties associated with it. The brosse kineties are composed of dikinetids whose anterior kinetosome bears a tangential transverse ribbon and whose posterior kinetosome bears the fibrillar associates typical of a somatic monokinetid. The oral dikinetids are oriented parallel to the circumference of the oral cavity, which is surrounded by oral papillae and oral ridges. Pairs of nematodesmata, originating from oral dikinetid kinetosomes, are typically triangular in transection. A phylogeny of rhabdophoran ciliates is presented using the mixed parsimony algorithm and is discussed with reference to the systematic revisions of the phylum Ciliophora.     

The Ultrastructure of Chaenea teres and an Analysis of the Phylogeny of the Haptorid Ciliates

Chaenea teres has typical haptorid ultrastructure. The somatic monokinetid has two transverse microtubular ribbons, an overlapping postciliary microtubular ribbon, and a laterally directed kinetodesmal fiber. The evered cytopharynx forms a dome at the apical end of the cell. The base of the dome is surrounded by oral dikinetids. The left, anterior kinetosome of the oral pair is not ciliated and has a transverse microtubular ribbon, a nematodesmata and a single postciliary microtubule. The right, posterior kinetosome is ciliated and has only postciliary microtubules. The kinetosomes at the anterior ends of the somatic kinetics are close together and their transverse microtubules and nematodesmata contribute to the support of the cytopharynx. The transverse microtubules of these oralized somatic kinetosomes, together with those from the oral dikinetids, line the cytopharynx. Accessory or bulge microtubules arise perpendicular to the transverse microtubules. A dorsal brush of three kineties of clavate cilia is found on the cell surface just posterior to the oral region. Mucocysts and a single type of toxicyst are present. The toxicysts are confined to the oral region. There are multiple ovoid macronuclei that stain weakly. Micronuclei were not observed. Cladistic analysis indicates the Chaenea may be most closely related to Fuscheria and Acropisthium. The cladistic analysis also suggests that existing taxonomies of the subclass Haptoria need to be revised. We propose some modifications to Foissner & Foissner's classification that include transferring Helicoprorodon, Actinobolina, the buetschiliids, and the balantidiids to the order Haptorida and recognizing the close relationship between pleurostomes and spathidiids.     

The fine structure of the paralabial organelle in the rumen ciliate Ophryoscolex purkinjei Stein, 1858

The paralabial organelle of the rumen ciliate Ophryoscolex purkinjei, located on the ventral side of the ciliophor, is a highly specialized part of the somatic cortex. It consists of alternating rows of short modified cilia and thin pellicular folds which form a ridge-like structure. The central "top kinety" is composed of monokinetids which bear cilia with 9 + 2 axonemes and 2 microns in length. The top kinety is accompanied by a comb-shaped fold on its distal side and by a broad wedge-shaped fold on its proximal side. To both sides there follow two or three lateral kineties made of dikinetids. The anterior kinetosome of each pair bears a clavate cilium, only 0.5-0.7 micron in length and with a 9 + 0 axoneme while the cilium of the posterior kinetosome is even shorter. Lateral folds with numerous microtubules cover these lateral kineties and rows of barren basal bodies. The fine structure of this supposed sensory organelle show a basic pattern in four other ophryoscolecids, and its increasing complexity parallels the suggested phylogenetic line of evolution of these ciliates.     

The Fine Structure of the Paralabial Organelle in the Rumen Ciliate Ophryoscolex purkinjei Stein, 1858

The paralabial organelle of the rumen ciliate Ophryoscolex purkinjei , located on the ventral side of the ciliophor, is a highly specialized part of the somatic cortex. It consists of alternating rows of short modified cilia and thin pellicular folds which form a ridge-like structure. The central "top kinety" is composed of monokinetids which bear cilia with 9 + 2 axonemes and 2 μm in length. The top kinety is accompanied by a comb-shaped fold on its distal side and by a broad wedge-shaped fold on its proximal side. To both sides there follow two or three lateral kineties made of dikinetids. The anterior kinetosome of each pair bears a clavate cilium, only 0.5–0.7 μm in length and with a 9 + 0 axoneme while the cilium of the posterior kinetosome is even shorter. Lateral folds with numerous microtubules cover these lateral kineties and rows of barren basal bodies. The fine structure of this supposed sensory organelle show a basic pattern in four other ophryoscolecids, and its increasing complexity parallels the suggested phylogenetic line of evolution of these ciliates.     

Ultrastructure of the cytoplasm of the lower holotrichous infusorian Tracheloraphis prenanti]

The ciliature of T. prenanti Dragesco 1960 (forma oligocineta Raikov et Kovaleva, 1968) consists of 14-18 ventral and lateral longitudinal kineties with paired kinetosomes, carrying either two cilia or one cilium per kinetosome pair (in the latter case, the nonciliated kinetosome is always the posterior one). The ectoplasmic fibrillar system belongs to the postciliary type. A pair of kinetosomes shares a common basal plate. The anterior kinetosome gives rise to a short ribbon of transverse microtubules, the posterior one, to a poorly developed kinetodesmal filament and to a strong ribbon of postciliary microtubules. The latter proceeds backwards along 8 to 12 kinetosome pairs, being incorporated into a laminated postciliodesma which accompanies each kinety on its right side. Rows of Golgi elements, sending secretory vesicles and channels towards the body surface, exist beneath the kinetosome bases. Each kinety is accompanied on its left by a microfibrillar myoneme, surrounded by perimyary vesicles and underlain by a row of mitochondria. The median part of the dorsal surface is nonciliated; the cytoplasm here is rich of membrane systems, contains peripheral, electron-dense, extrusible inclusions and sometimes also bacteria. The electron-dense inclusions develop in the endoplasm, in close contact with mitochondria. The endoplasm contains also large microfibrillar spheres of unknown nature.     

Light and Electron Microscopical Observations on the Stomatogenesis of the Ciliate Coleps amphacanthus Ehrenberg, 1833

Light and electron microscopical observations on the stomatogenesis of Coleps amphacanthus Ehrenberg, 1833, show that this "gymno"-stome ciliate has a well developed oral ciliature made of 19–23 "paroral dikinetids" and three "adoral organelles." These structures were previously known as "circumoral ciliature" and "dorsal brosse," and it was thought that they originated from the distal ends of all the 22–26 somatic kineties. Contrary to this view, only four stomatogenic kineties (K1, Kn, Kn-1, and Kn-2) are involved in stomatogenesis of the opisthe. All paroral dikinetids arise from one single kinetofragment (KF1) to the right of the oral anlage while the adoral organelles originate from the three left kinetofragments (KFn, KFn-1, and KFn-2). In particular, the future paroral dikinetids perform a complex morphogenetic movement that leads to a situation where the postciliary microtubules of the once posterior kinetosome of each oral dikinetid give rise to the cytopharyngeal microtubular ribbons. The postciliary origin of the cytopharyngeal ribbons which could only be detected by an EM study of stomatogenesis shows that the basket of Coleps belongs to the cyrtos-type and not to the rhabdos-type basket, where transverse microtubules accompany the basket-forming nematodesmata. The taxonomic implications of these observations, which may lead to a revision of the systematic position of the genus Coleps , are discussed.     

Etude Ultrastructurale du CiliéKuklikophrya dragescoi gen. n., sp. n.*

SYNOPSIS The cortical infraciliature of Kuklikophrya dragescoi gen. n., sp. n. is composed of double kinetosomes. Each kinetosome has transverse fibers. The anterior transverse fibers are associated with a sheet of dense material and the posterior transverse fibers are directed toward the posterior part of the body. The posterior kinetosome of a pair has only a short protuberance in the position of the kinetosomal fiber. The cortex has a well developed alveolar layer and a thick ecto-endoplasmic boundary. A distinctive characteristic of the buccal ciliature is the circumoral ciliature whose infraciliature is made up of pairs of cilia-bearing kinetosomes. The antero-posterior polarity of the paroral segment is in inverse relationship to that of the remaining ciliature of the organism. The adoral and preoral ciliary organelles consist of 2 rows of kinetosomes, each of which bears postciliary fibers. A frame of nematodesmata surrounds the cytopharynx which is supported by microtubular bands which impart to it a very specific laminated appearance. The “phagoplasm” is formed by “vermicelli”-like vesicles. The micronucleus is found in the perinuclear area of the macronucleus.     

A Reexamination of the Ultrastructure of Didinium nasutum and a Reanalysis of the Phylogeny of the Haptorid Ciliates

ABSTRACT. The cilia of Didinium nasutum are restricted to two girdles encircling the cell. Each row of cilia in both girdles is made up of two to three anterior pairs of kinetosomes followed by several single kinetosomes. Each single kinetosome has two sets of transverse microtubules, an overlapping postciliary microtubular ribbon, and a laterally directed kinetodesmal fiber. The pairs of kinetosomes are homologous to the oral dikinetids of other haptorians: the nonciliated kinetosome of the pair has a transverse microtubular ribbon that extends to line the membrane of the proboscis, a single short postciliary microtubule, and a nematodesma; the ciliated kinetosome has a ribbon of postciliary microtubules and two sets of transverse microtubules. The presence of these characters in Didinium invalidates Leipe & Hausmann's conclusion that the Didiniidae should be removed from the subclass that contains the other haptorians (Leipe, D. D. & Hausumann, K. 1989. Somatic infraciliature of the haptorid ciliate Homalozoon vermiculare (Kinetofragminophora, Gymnostomata) Ditransversalia n. subcl. and phylogenetic implications. J. Protozool. , 36 :280–289). In light of this, the justification for a subclass Ditransversalia is challenged and shown to be unnecessary.     

Fine Structure and Molecular Phylogeny of Parametopidium circumlabens (Ciliophora: Armophorea), Endocommensal of Sea Urchins

Metopid armophoreans are ciliates commonly found in anaerobic environments worldwide; however, very little is known of their fine structure. In this study, the metopid Parametopidium circumlabens (Biggar and Wenrich 1932) Aescht, 1980, a common endocommensal of sea urchins, is investigated for the first time with emphasis on transmission electron microscopy, revealing several previously unknown elements of its morphology. Somatic dikinetids of P. circumlabens have a typical ribbon of transverse microtubules, an isolated microtubule near triplets 4 and 5 of the anterior kinetosome, plus two other microtubules between anterior and posterior kinetosomes, a short kinetodesmal striated fiber and long postciliary microtubules. In the dikinetids of the perizonal stripe, the kinetodesmal fiber is very pronounced, and there is a conspicuous microfibrillar network system associated with the kinetosomes. A new structure, shaped as a dense, roughly cylindrical mass surrounded by microtubules, is found associated with the posterior kinetosome of perizonal dikinetids. The paroral membrane is diplostichomonad and the adoral membranelles are of the “paramembranelle” type. Bayesian inference and maximum‐likelihood analysis of the 18S‐rDNA gene unambiguously placed P. circumlabens as sister group of the cluster formed by ((Atopospira galeata, Atopospira violacea) Metopus laminarius) + Clevelandellida, corroborating its classification within the Metopida.     

Light and Electron Microscopic Observations on the Heterotrich Ciliate Climacostomum virens

SYNOPSIS. Alveolar membranes and an epiplasm exist under the cell membrane of the noncontractile heterotrich ciliate Climacostomum virens. Postciliary microtubular ribbons join at the right of each somatic kinety to form a Km fiber. Two transverse microtubular fibers occur per kinetosomal pair. A myonemal network interconnects the kinetosomal bases intrakinetally and interkinetally. Ultrastructural comparisons are made between the contractile and noncontractile heterotrichs.
The buccal cortex consists of an adoral zone of membranelles, a peristomal field, a buccal tube, the apical membranelles, and a haplokinety. The kineties of the peristomal field and buccal tube are rows of paired kinetosomes, with a postciliary ribbon of microtubules arising from the posterior kinetosome of each pair, and a transverse ribbon and an oblique ribbon from the anterior kinetosome. No Km fibers exist in this region. The haplokinety is a collar of paired kinetosomes surrounding the cytostome; a postciliary microtubular ribbon descends from each kinetosomal pair into the cytostomal region. Ultrastructural details of the buccal cortex of C. virens and other heterotrichs are compared. The nemadesmata which lie under the membranelles are implicated in the body bending of C. virens.
Algae endosymbiotic in the cytoplasm of C. virens are described.     

Somatic and Oral Cortical Ultrastructure of the Plagiopylid Ciliates Lechriopyla mystax Lynch, 1930 and Plagiopyla minuta Powers, 19331

The somatic and oral cortical ultrastructure of the plagiopylid ciliates Lechriopyla mystax Lynch, 1930 and Plagiopyla minuta Powers, 1933 are described. The somatic kinetids are monokinetids with an anteriorly directed kinetodesmal fibril originating near triplets 5, 6, 7, a divergent postciliary ribbon originating at triplet 9, and an unusual transverse ribbon originating in dense material adjacent to triplets 1, 2, 3. The transverse ribbon extends beneath the right surface of the cortical ridge adjacent to the kinety from which it originated. The oral kinetids are also monokinetids from whose base rootlet fibrils extend inwards beneath the oral kineties and converge on the furcula. The striated band on these ciliates is composed of a series of short ridges orthogonal to the longitudinal axis of the band. The sides of the striated band groove are apparently supported by macrotubules. The cortical ultrastructure of the plagiopylids is discussed with reference both to the optical microscopy of the organisms and to the ultrastructure of other ciliate taxa. The plagiopylids are not clearly related to any other higher taxon and are placed incertae sedis in the Subphylum Cyrtophora Small, 1976.     

Updating the Trachelocercids (Ciliophora, Karyorelictea). I. A Detailed Description of the Infraciliature of Trachelolophos gigas N. G., N. Sp. and T. filum (Dragesco & Dragesco-Kernéis, 1986) N. Comb

ABSTRACT. Trachelolophos gigas n. g., n. sp. and T. filum (Dragesco & Dragesco-Kernéis, 1986) n. comb. (basionym: Tracheloraphis filum) were discovered in the mesopsammon of the French Atlantic coast at Roscoff. Their morphology and infraciliature were studied in live and protargol impregnated specimens. The new genus, Trachelolophos, belongs to the family Trachelocercidae and is unique in having a conspicuous ciliary tuft, which is very likely a highly modified brosse, in the oral cavity. The two species investigated have a very similar infraciliature, differing only in morphometric characteristics and in the nuclear configuration. The entire somatic and oral infraciliature consists of dikinetids which have both basal bodies ciliated or only the anterior or posterior ones, depending on the region of the cell. The right side is densely and uniformly ciliated. Its kineties extend onto the left side to the glabrous stripe, where an anterior and posterior secant system are formed, reducing the number of kineties in the narrowed neck and tail region. The left side bears a narrow glabrous stripe bordered by slightly irregularly arranged dikinetids having rather stiff cilia (bristles), possibly forming an uninterrupted, prolate ellipsoidal (bristle) kinety as indicated by their ciliation. The bristle kinety commences subapically at the right margin of the glabrous stripe, extends posteriorly, then anteriorly at the left, to end up at the right margin again. The dikinetids of the right posterior portion of the bristle kinety have the posterior basal bodies ciliated, whereas the anterior basal bodies are ciliated in its left and right anterior portion. The ends of the bristle kinety meet distinctly subapically at the right margin of the glabrous stripe, as indicated by the diametrically opposed ciliation of the dikinetids. The anterior region (head) of the cell bears a distinct circumoral kinety composed of very regularly arranged dikinetids, associated with nematodesmata forming an oral basket together with the nematodesmal bundles originating from the oralized somatic dikinetids at the anterior end of the somatic kineties. The systematics of trachelocercid ciliates are briefly reviewed and discussed.     

Transmission Electron Microscopical Observations on Stomatogenesis during Metamorphosis of Eufolliculina uhligi (Ciliophora: Heterotrichida)1

Stomatogenesis during metamorphosis of the marine loricate ciliate, Eufolliculina uhligi, was observed by transmission electron microscopy. Kinetosome proliferation in the stomatogenic territory leads to the formation of an anarchic field. This separates into the left adoral and the right paroral primordia. Both primordia consist of pairs of kinetosomes. One kinetosome of a pair is associated with one transverse and two postciliary microtubules; the other has one transverse microtubule. The postciliary microtubules of the adoral kinetosomes become divergent; those of the paroral kinetosomes become convergent. The adoral kinetosomes arrange in promembranelles. Then a third row of kinetosomes is produced anteriorly to each promembranelle. This third row is short at the peristome but longer in the buccal area. The paroral kinetosomes form a stichodyad. The buccal part of the paroral primordium is resorbed during formation of the buccal cavity. Stomatogenesis ends with the development of a functioning cytostome. During this process, the postciliary microtubules of the buccal adoral membranelles elongate and become associated with cytopharyngeal vesicles. Fusion of these vesicles with the cytostome has been observed some time after the completion of the oral structures.     

The Ultrastructure of Zosterodasys agamalievi (Ciliophora: Synhymeniida)

ABSTRACT. The cell surface of the synhymeniid ciliate, Zosterodasys agamalievi , consists of shallow kinetal grooves separated by low cortical ridges. Numerous electron-opaque bodies are located in the cortical ridges, inside the kinetal grooves, and are distributed in parallel rows between adjacent kineties. Well-developed alveoli are present beneath the cell surface membrane. Zosterodasys agamalievi has a single micronucleus and a homomerous macronucleus. The infraciliature of the somatic monokinetid consists of an anteriorly-directed kinetodesmal fiber, a well-developed divergent postciliary microtubular ribbon, radially-oriented transverse microtubules, and a short striated rootlet, which extends anteriorly from the base of the kinetosome into the cell. Zosterodasys agamalievi has a perioral band of paired cilia, the synhymenium, that winds obliquely across the ventral surface of the body, just posterior to the cytostome. The infraciliature of the anterior kinetosome of the synhymenium consists of two postciliary microtubules; a well-developed, divergent post-ciliary ribbon of microtubules and a short kinetodesmal fiber are associated with the posterior kinetosome. The cytopharynx is supported by 14-16 nematodesmata which are capped distally by a capitulum. The cytopharynx is bound proximally by a fibrous sheath and is lined by radially-arranged microtubular ribbons. No obvious oral ciliature is present.     

THE ORGANIZATION AND EVOLUTION OF MICROTUBULAR ORGANELLES IN CILIATED PROTOZOA

(1) Ciliated protozoa are viewed as unicellular organisms structured in a hierarchy of organizational levels that include the macromolecular, suborganellar, unit organellar, organellar complex, and organellar system. (2) The ciliate cortex is divided into two major functional regions, the somatic region and the oral region. The fundamental component of the cortex is an organellar complex, the kinetid, whose organizing centre is the kinetosome with which are associated three fibrillar associates diagnostic of ciliates. These three fibrillar associates are the periodically striated kinetodesmal fibril and two microtubular ribbons, the transverse and postciliary ribbons. (3) Somatic and oral kinetids are found to be of three major types: monokinetids are composed of one kinetosome and its fibrillar associates; dikinetids are composed of two kinetosomes and their fibrillar associates; polykinetids are composed of more than two kinetosomes and their fibrillar associptes. (4) The mechanisms underlying kinetid function and development remain largely unexplored. Research into the molecular biology and ultrastructure, especially of mutant forms, should provide basic insights in the near future. (5) The conservation of kinetid structure across major phyla of organisms suggests that this subcellular structure should be useful in phylogenetic analysis despite the concepts of ‘chemical identity’ and ‘organic design’. (6) The evolutionary rate of change of oral features is greater than that of somatic features, probably due to developmental and ecological factors. Nevertheless both cortical regions are constrained by the phenomenon of structural conservatism; that is, the conservation of structure through time is inversely related to the level of biological organization. (7) Eight major groupings of ciliate species are recognized, based on ultrastruc-tural features of the cortex. Several examples of differences between these eight groups and the groups presently recognized are discussed.     

The Fine Structure of Saprodinium dentatum Lauterborn, 1908 as a Representative of the Odontostomatida (Ciliophora)

The fine structure of the sapropelic ciliate Saprodinium dentatum is described based on phase-contrast microscopy, silver-staining techniques, cryo-fracture scanning electron microscopy, and thin sections. The study concentrates on a detailed analysis of the somatic cortex and the oral ciliature of this highly asymmetric, laterally compressed ciliate. The cell shape is dominated by a number of site-specific spines and the curving course of 10 somatic kineties (SK 1–10). The SK, composed of dikinetids, show an intrakinety differentiation that seems characteristic for other odontostomes as well. The anterior segment of the SK is mostly ciliated, followed by a non-ciliated segment in which the kinetosomes lack all typical fiber systems. Except for SK 4–6, the posterior segment is ciliated again, forming the spine kinetics associated with particular caudal spines. The anterior segment of SK 3 through SK 7 form the frontal band, which together with the two frontal kineties constitutes the main locomotory organelle for a ciliate that creeps on the substratum. A short kinety with inverse polarity, not seen in earlier light microscopical studies, was observed near the oral spine. We made particular effort to find a logical explanation for the observed association of the SK with the various caudal spines. The oral ciliature consists of nine adoral organelles located in a tripartite oral cavity. The absence of a paroral ciliature together with the position of the cytostome anterior to the adoral organelles may be the result of rotational movement of the oral apparatus during the evolution of these bizarre ciliates. Results are discussed with special reference to the phylogenetic relationship of the Odontostomatida to the Heterotrichida and no conclusive answer was found in this first electron microscopical study of an odontostomatid ciliate.     

Somatic kinetics or paroral membrane: which came first in ciliate evolution?

The ciliate species which lack a distinctive oral ciliature are considered to represent an ancestral state in ciliate evolution. Consequently, the somatic kineties composed of kinetids (kinetosomes plus cilia and associated fibrillar systems) are thought to be the ancestral ciliature. Results on stomatogenesis in 'gymnostomial ciliates' have shown that these ciliates probably have evolved from ancestors already equipped with an oral ciliature. Thus instead of the somatic, the oral ciliature may be regarded an ancestral. Based on these ideas a hypothesis on the evolution of the ciliate kinetome (assembly of all kinetids covering the body of a given ciliate) is presented. The first step in the evolution of the kinetome was the formation of a paroral membrane, a compound ciliary organelle lying along the right side of the oral area which historically but falsely is termed membrane. It was composed of kinetosomal dyads (dikinetids), derived from the kinetid of a dinoflagellate-like ancestor. From the beginning the paroral membrane was responsible for locomotion, ingestion and for the formation of a cytopharyngeal tube which the first ciliate probably had inherited from its flagellate ancestor. In the second step a first somatic kinety was formed from the right row of kinetosomes of the paroral membrane as a result of a longitudinal splitting of the paroral membrane and a subsequent migration of the forming kinety to the right into the somatic cortex. To increase the number of somatic kineties this process was repeated until the kinety produced first reached the left border of the oral area. By this step the locomotive and the nutritional functions were differentiated between somatic and oral structures. In a third step the adoral organelles were formed from somatic kinetids left of the oral area. The primitive type of stomatogenesis was a buccokinetal one derived from the mode the flagellate ancestor used to distribute its replicated kinetosomes to the offspring cells (buccokinetal means that at least parts of the oral anlage for the posterior offspring cell has its origin in the parental oral apparatus). This hypothesis, based on comparative studies on ciliate morphogenesis, is corroborated by molecular data from other laboratories.