Notes: [Auszug] It is generally assumed that the first fossil appearance of a group of organisms corresponds to its evolutionary origin. But we have molecular evidence that extant members of the most abundant microfossil-forming group, the Foraminifera, include ‘naked’ amoeboid species, indicating ...

Notes: RESUME. Dans la région antérieure de Spirochona gemmipara, l'emploi combiné de la microscopie à contraste interférentiel (No-marski), des colorations au protargol et de la microscopie électronique à transmission révèle l'existence d'un appareil cytoproctal et d'un système excréteur (“contractile vacuole complex”), lesquels ont souvent été confondus entre eux ou avec le cytopharynx. L'appareil cytoproctal comprend un orifice externe situéà la base de la collerette, un canal cytoproctal long d'environ 20 μm limité par une pellicule alvéolaire, et le cytoprocte proprement dit. Le système excréteur est formé de 6 à 8 canaux sinueux pouvant mesurer jusquà 20 μm de long et s'ouvrant chacun par un pore situé sur la face interne de la collerette, parmi la ciliature. L'ostium, c'est-à-dire l'orifice profond de chaque canal, est en relation avec une vacuole dans laquelle aboutit un spongiome tubulaire bien développé. Bien que profondément enfoncés dans le cytoplasme, le cytoprocte et les ostia du spirochone ne semblent pas fondamentalement diffêrents des organites correspondants décrits chez Paramecium et chez Tetrahymena.

Notes: . Large miliolid foraminifers of the subfamily Soritinae bear symbiotic dinoflagellates morphologically similar to the species of the “Symbiodinium” complex, commonly found in corals and other marine invertebrates. Soritid foraminifers are abundant in coral reefs and it has been proposed that they share their symbionts with other dinoflagellate-bearing reef dwellers. In order to test this hypothesis, we have analysed partial large subunit ribosomal DNA sequences from dinoflagellates symbionts obtained from 28 foraminiferal specimens, and compared them to the corresponding sequences of Symbiodinium-like endosymbionts from various groups of invertebrates. Phylogenetic analysis of our data shows that all soritid symbionts belong to the “Symbiodinium” species complex, within which they form seven different molecular types (Fr1–Fr7). Only one of these types (Fr1) branches within a group of invertebrate symbionts, previously described as type C. The remaining six types form sister groups to coral symbionts previously designed as types B, C, and D. Our data indicate a high genetic diversity and specificity of Symbiodinium-like symbionts in soritids. Except for type C, we have found no evidence for the transmission of symbionts between foraminifers and other symbiont-bearing invertebrates from the same localities. However, exchanges must have occurred frequently between the different species of Soritinae, as suggested by the lack of host specificity and some biogeographical patterns observed in symbiont distribution. Our data suggest that members of the subfamily Soritinae acquired their symbionts at least three times during their history, each acquisition being followed by a rapid diversification and independent radiation of symbionts within the foraminiferal hosts.

Notes: Over the past few years, the use of cultivation-independent techniques to detect eukaryotic diversity has proven to be a powerful approach. Based on small-subunit ribosomal RNA (SSU rRNA) gene analyses, these studies have revealed the existence of an unexpected variety of new phylotypes. Some of them do not seem to be related to any molecularly described lineage, and have been proposed to represent novel eukaryotic kingdoms. In order to critically review the evolutionary importance of this novel high-level eukaryotic diversity and to test the potential technical and analytical pitfalls and limitations of eukaryotic environmental DNA surveys (EES), we analysed 484 environmental SSU rRNA gene sequences, including 81 new sequences from sediments of the river Seymaz (Geneva, Switzerland). Based on a detailed screening of an exhaustive alignment of SSU rRNA gene sequences and the phylogenetic re-analysis of previously published sequences using Bayesian methods, our results suggest that the number of novel higher-level taxa revealed by previous EES was over-estimated. Three main sources of errors are responsible for this situation, namely (1) the presence of undetected chimeric sequences; (2) the misplacement of several fast evolving sequences; and (3) the incomplete sampling of described, but yet unsequenced eukaryotes. EES undoubtedly contribute to unravel many novel eukaryotic lineages, but there is no clear evidence for a spectacular increase of the diversity at a megaevolutionary level. After our re-analysis, we found only five candidate lineages of possible novel high-level eukaryotic taxa. To ascertain their taxonomic status, however, the organisms themselves have to be identified now.

Notes: Molecular sampling of the taxonomic diversity of the living world is nowadays a task of paramount importance. Heliozoa represents one of the major eukaryotic taxa, which remain significantly underrepresented in molecular databases. The term Heliozoa was coined to embrace organisms with a rounded body and stiff pseudopodia. Despite evidences from ultrastructural studies, which conclusively show the polyphyly of selected heliozoan groups, contemporary morphological systems retain Heliozoa as a monophyletic taxon. From the perspective of reconstructing the true phylogeny of Eukaryota, molecular approaches to analyse relationships within this large protist group are evidently necessary. Phylogenetic analysis of our data shows that the four heliozoan taxa branch either independently or within different eukaryotic phyla. The actinophryids (Actinosphaerium, Actinophrys) appear as a lineage of stramenopiles, while the desmothoracids (Clathrulina, Hedriocystis) branch within “core Cercozoa”. The position of both groups is strongly supported in all analyses and is congruent with ultrastructure-based taxonomic revisions. The centrohelids (Chlamydaster, Heterophrys, Pterocystis, and Raphidiophrys) do not seem to be related to any particular eukaryotic phylum, in agreement with a recent molecular study. The taxopodid Sticholonche was found to branch between Polycystinea and Acantharea, two classes of radiolarians. Results obtained in this study suggest that the heliozoan body form cannot be used as a diagnostic argument to unite Heliozoa. Instead, we discriminate between the three heliomorphic taxa of independent origin, Actinophryida, Desmothoracida and Sticholonche, and propose the novel higher rank taxon Centrohelida. The term Heliozoa should thus be used solely in historical context.

Notes: Lobose amoebae are abundant free-living protists and important pathogenic agents, yet their evolutionary history and position in the universal tree of life are poorly known. Molecular data for lobose amoebae are limited to a few species, and all phylogenetic studies published so far lacked representatives of many of their taxonomic groups. Here we analyse actin and small-subunit ribosomal RNA (SSU rRNA) gene sequences of a broad taxon sampling of naked, lobose amoebae. Our results support the existence of a monophyletic Amoebozoa clade, which comprises all lobose amoebae examined so far, as well as the amitochondriate pelobionts and entamoebids, and the slime molds. Both actin and SSU rRNA phylogenies distinguish two well-defined clades of amoebae, the “Gymnamoebia sensu stricto” and the Archamoebae (pelobionts+entamoebids), and one weakly supported and ill-resolved group comprising some naked, lobose amoebae and the Mycetozoa.

Notes: . Xenophyophorea are giant deep-sea rhizopodial protists of enigmatic origins. Although species were described as Foraminifera or sponges in the early literature, the xenophyophoreans are currently classified either as a class of Rhizopoda or an independent phylum. To establish the phylogenetic position of Xenophyophorea, we analysed the small subunit (SSU) rRNA gene sequence of Syringammina corbicula Richardson, a newly described xenophyophorean species from the Cape Verde Plateau. The SSUrDNA analyses showed that S. corbicula is closely related to Rhizammina algaeformis, a tubular deep-sea foraminiferan. Both species branch within a group of monothalamous (single-chambered) Foraminifera, which include also such agglutinated genera as Toxisarcon, Rhabdammina, and Saccammina, and the organic-walled genera Gloiogullmia and Cylindrogullmia. Our results are congruent with observations of similar cytoplasmic organisation in Rhizammina and Syringammina. Thus, the Xenophyophorea appear to be a highly specialised group of deep-sea Foraminifera.

Notes: The regeneration (RG) of the oral apparatus (OA) by Climacostomum virens (Ciliophora, Heterotrichida) is examined by estimation of the ability of live cells to ingest food as well as by Nomarski interference contrast microscopy, bright field microscopy of protargol-stained specimens, and by scanning electron microscopy. When placed in a 6% (w/v) urea solution for ∼ 2 min 10 sec, populations of 10,000–100,000 cells shed a large part of their OA. In more than 90% of the cells that shed, the discarded segment is comprised of the apical membranelles, most of the adoral membranelles, and of a variable part of the buccal tube. After washing and incubation at 26°C, 50% of the cells regenerate a functional OA in 4 h 47 min, and after 5 h 26 min, 90% of the cells are able to ingest food. At any given moment during the process, 50–90% of the cells are morphologically in the same stage of RG.Seven stages (among which three are divided into two substages) of RG are defined. The process begins by the disorganization of the remnant oral structures. Concomitantly, kinetosomes multiply along the kineties of the zone of discontinuity and form the longitudinally oriented oral primordium. The latter gives rise to the adoral primordium, which rapidly produces the adoral zone of membranelles (AZM), and to the paroral primordium, which subsequently forms the apical membranelles, the buccal peristomial kineties, and the paroral kinety. Morphogenetic movements lead to incurvation of the AZM and the frontal field and to invagination of the buccal tube.

Notes: The holdfast apparatus fills the posterior half of the larva; it is comprised of cytoplasmic granules called heterosomes and of about twenty collecting canals which converge at a septate chamber, the rosette. The latter opens to the exterior by a secretory appendage called the podite. My hypothesis is that, when the larva attaches to a substrate, the heterosomal contents empty into the collecting canals and are mixed in the rosette. With the aid of the podite, this secretion is applied to the gill substrate where it forms the so-called style of the future adult. The holdfast apparatus of the adult Spirochona comprises two regions of different nature: the pseudostyle, which is the posterior part of the cell, and the style which is an extracellular secretion. The style looks like a truncated cone and adheres firmly to the substrate. The upper face of the style shows 16–18 stylonemes which are inserted in the crypts of the pseudostylar rosette. The latter corresponds to the larval rosette, and the crypts communicate with a chamber and numerous suprastylar acini, which represent the remnants of the larval collecting canals. Except for a few details, the holdfast apparatus appears to be similar among all the chonotrichs studied to date. This apparatus differs from that of the Suctoria and of the Peritricha. It has some analogies with the “mouth-rosette” complex of the Apostomatida. Finally, the presence of a podite in a chonotrich larva is new evidence supporting a closer systematic relationship between the Chonotrichida and the Dysteriidae.〈section xml:id="abs1-2"〉〈title type="main"〉RESUMEL'appareil de fixation occupe la moitié postérieure de la larve; il est composé de granules cytoplasmiques, les hétérosomes, et d'une vingtaine de canaux collecteurs convergeant vers une chambre septée appelée rosette. Celle-la communique avec l'extérieur par un appendice sécréteur, le podite. II est supposé que, lors de la phase d'attachement, le matériel contenu dans les hétérosomes se vide dans les canaux collecteurs et se mélange dans la rosette, puis, grâce au podite, est appliqué sur la branchie où il forme le pied ou style du futur adulte. L'appareil de fixation de l'adulte comprend donc deux parties de nature différentes: le pseudostyle, c'est-à-dire la région postérieure du corps cellulaire, et le style, une sécrétion extracellulaire. Celui-ci forme une masse tronconique intimement fixée au substrat. Sur sa face supérieure, le style porte 16–18 stylonèmes enserrés dans les cryptes de la rosette pseudostylaire. Celle-ci correspond à la rosette larvaire, et les cryptes communiquent avec une chambre et des acini suprastylaires, eux-mêmes vestiges des canaux collecteurs larvaires. A quelques détails près, il semble bien que l'appareil de fixation des Chonotriches actuellement étudiés soit construit sur le même type. Cet appareil de fixation est différent de celui des Suctoria et des Peritricha; il présente peut-être quelques similitudes avec le complexe “bouche-rosette” des Apostomatida. Enfin, la présence d'un podite chez une larve de Chonotriche est un argument nouveau en faveur du rapprochement Chonotrichida–Dysteriidae.

Notes: Les colorations au protargol ainsi que la microscopie électronique á transmission et á balayage permettent de distinguer quatre parties dans I'organisation de Spirochona gemmipara: la collerette formée d'une entonnoir et d'une volute abritant la ciliature, le pseudatrium, et le cytostome; le cou contenant le cytopharynx, le systéme excréteur. et I'appareil cytoproctal; le corps renfle par les noyaux et les vacuoles digestives: et le pseudostyle allonge assurant la fixation au substrat. En majeure partie, le spirochone est limité par une pellicule non ciliée et dépourvue de cils; la pellicule comprend la membrane cellulaire, un épiplasme épais percé de nombreux pores et des triplets de microtubules (MT) sous-pelliculaires. Principalement située dans I'entonnoir, la ciliature somatiquc du spirochone est répartie en deux ensembles inégaux, le champ gauche et le champ droit. Les cinéties sont séparées par des crétes contenant les MT post-ciliaires disposés en une couche verticale; les MT sous-cinétiens sont nombreux, arrangés parallélement á la base des cinétosomes; ceux-lá présentent également une lame dense et des MT transverses, et une fibre cinétodesmale discrete. Un important réseau de faisceaux fibrillaires est disposé orthogonalement par rapport aux cinéties. La base de I'entonnoir est déprimée en une petite cavitéévasée, le pseudatrium; celui-lá conduit à un cytostome ouvert en permanence. Dépourvu de némadesmes, le cytopharynx est un tube cylindrique formé par une dizaine de rideaux microtubulaires; prés du cytostome, chaque rideau porte en plus quelques MT radiaires assimilés aux lamelles Z des Nassulida. Le phagoplasme est riche en tubules complexes et en vésicules de taille moyenne à contenu contrasté. Le champ X, peu organisé, comprend 10–30 cinétosomes situés à gauche du cytostome; il ne correspond certainement pas á la ciliature périorale droite de Chilodochona. Si cette difference se retrouve chez d'autres Chonotriches, il sera nécessaire de séparer taxonomiquement les espéces possédant une ciliature périorale de celles qui en sont dépourvues.〈section xml:id="abs1-2"〉〈title type="main"〉ABSTRACTIn the organization of Spirochona gemmipara, four parts can be demonstrated by protargol staining and also by scanning and transmission electron microscopy: the collar, composed of a funnel and a volute, which shelters the cilia, the pseudatrium, and the cytostome: the neck, which contains the cytopharynx, the excretory system, and the cytoproctal apparatus; the body, enlarged by the nuclei and the digestive vacuoles; and the elongated pseudostyle, which ensures attachment to the substrate. Most of the surface of the spirochone is covered by the pellicula devoid of cilia and alveoli; the pellicula comprises the cell membrane, a thick epiplasm perforated with numerous pores and subpellicular triplets of microtubules (MT). The somatic ciliature of the spirochone is located principally in the funnel and is divided into two unequal parts, the left and right fields. The kineties are separated from one another by ridges, each containing one layer of postciliary MT: numerous subkinetal MT run in a parallel direction under the kinetics; moreover, the kinetosomes show a transverse dense spur and MT, and a modest kinetodesmal fiber. A conspicuous net of fibrillar bundles runs orthogonally to the kineties. The base of the funnel forms a small splayed depression, the pseudatrium; the latter leads to a permanently open cytostome. The cytopharynx is a cylindrical tube devoid of nematodesmata but containing ca. 10 microtubular curtains, each bearing also some radial MT resembling the Z lamellae of the Nassulida. The phagoplasm contains many complex tubules and numerous middle-sized vesicles with an electron-dense content. The X field, which is not well organized and comprises 10–30 kinetosomes, lies on the left of the cytostome; it certainly does not correspond to the right perioral ciliature of Chilodochona. If this disparity is found again in other chonotrichs, it will be necessary to separate taxonomically the species that possess a perioral ciliature from those that do not.