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The morphology of some brackish water oligotrichs was investigated using in vivo, Lugol fixed and protargol impregnated material. One new species is described, Strombidium triquetrum nov. spec; Pelagohalteria cirrifera (Kahl, 1935) Foissner, Skogstad & Pratt, 1988, Strombidium conicum (Lohmann, 1908) Wulff, 1919, and S. vestitum (Leegaard, 1915) Kahl, 1932 are redescribed. Additionally, two unnamed species belonging to the genera StrombidiumClaparède & Lachmann, 1859 and CyrtostrombidiumLynn & Gilron, 1993 are described. Ecological data concerning maximum abundances, abundances at different salinities and temperatures, as well as contents of food vacuoles are given. The genus CiliospinaLeegaard, 1915 and its single species, Ciliospina norvegicaLeegaard, 1915, are regarded as nomina dubia.

The morphology, nuclear apparatus, infraciliature, and silverline system of two populations of the Euplotes woodruffi-complex, one from brackish water off Pamlico Sound, North Carolina (USA), and the other from a freshwater pond in Qingdao (P.R. China), have been examined in vivo and with silver nitrate and protargol impregnations. A comparison of the two forms reveals marked differences in structure sufficient to separate the two morphotypes into two species. Euplotes parawoodruffi n. sp. (syngen 1 of E. woodruffi) is characterized by a strongly arched dorsum, regular double-eurystomas type silverline system, an adoral zone of ca. 80 membranelles extending over 4/5 of the cell length; 9 frontoventral, 2 marginal, and 2 caudal cirri; marine/brackish biotope; macronucleus irregularly T-shaped. Its T-shaped macronucleus with a short right arm differs from that of E. woodruffi, in which the right arm is longer than the left. The general body shape of E. parawoodruffi, broad anteriorly and tapering posteriad, differs from the ovoid shape of E. woodruffi. Its domed dorsum without longitudinal grooves differs from the flattened dorsum with shallow grooves of E. woodruffi. The presence of a longer AZM formed of consistently more membranelles and the absence of a pre-oral pouch (an invagination on the dorsal wall of the buccal field anterior to the cytostome, always present in E. woodruffi) further separates E. parawoodruffi from the latter.

The chrysophyte stomatocyst flora from 36 moss samples from Stromness Bay area on the subantarctic island of South Georgia is decribed, using both light and scanning electron microscopy. A total of 46 morphotypes were recorded. Thirty-four of them are newly described in this paper, following the guidelines of the International Statospore Working Group (ISWG). This is the first paper dealing with chrysophyte stomatocysts from South Georgia.

An ultrastructural study of Hyalophysa's phoront revealed that ciliary absorption and kinetosomal absorption are two distinct events. During the transformation from the tomite (microstome) to the meridional phoront stage, the ogival field (OG) loses its cilia. Ciliary loss involves an in situ disassembly of the structure and does not involve the retraction of axonemes into the cytoplasm or the detachment of cilia from the cell surface. The end result of the deciliation is a bald kinetosomal field. Pellicular folds, perhaps exaggerated to accommodate newly available membrane, are pronounced. Following deciliation, the kinetosomes of the OG are absorbed. The kinetosomes are disassembled in situ as well, as they are always located at the inner membrane of the pellicle and never detached from the cell surface or within autophagic vacuoles. Ciliary loss and kinetosomal absorption also occur in the falciform fields (FFs). Deciliation begins first, followed by the loss of two rows of kinetosomes in FF9. The end result is a FF9 and FF8 that are two kinetosomes wide and lack cilia. The mechanism of ciliary and kinetosomal loss is the same as in the OG. The reorganization of the OG and FFs is a necessary event in the metamorphosis of the crawling tomite stage (microstome) to the trophont (macrostome), as the ventral surface of the trophont develops an extensive extended cytostome. The reduction of the OG and FFs possibly provides tubulin and membrane reserves for the development of the somatic ciliature and extended cytostome in the trophont.

Two populations of cyanophytes that produce screw-like coiled trichomes were examined in order to elucidate their taxonomic position. The first population was collected in an Amazonian reservoir in June 1989. From the investigations of this species, it was possible to establish a new species of Arthrospira (A. skujae) that had previously been classified by Skuja (1949) from Burma under the name “Spirulina gigantea” (sine typo). The second, similar population was collected in the littoral zone among water plants, of a small, shallow pond in the southeastern part of Brazil, which corresponded to Arthrospira jenneri. Both species were evaluated statistically, and the measurements, drawings, photos and comparisons with closely related species are presented.

During conjugation of Blepharisma, only some micronuclei enter meiosis. Other micronuclei, called somatomicronuclei, do not degenerate but differentiate directly into macronuclear anlagen (secondary anlagen) without meiosis and karyogamy. Normal (primary) anlagen develop from synkaryon derivatives. We observed these processes at the ultrastructural level.

In early conjugation (0–2 hours after pair formation), all micronuclei swell. This correlates with decondensation of the micronuclear chromatin. At 3 hours, the micronuclei differentiate into somatic and meiotic (leptotene) ones: the latter develop bundles of microtubules. The somatomicronuclei remain homogeneous and lack microtubules. At 8–9 hours meiotic micronuclei display synaptonemal complexes and thus are in pachytene; at the same time, structures in form of loose chromatin patches first appear in somatomicronuclei. The patches gradually condense and become conspicuous at 10–12 hours (stages from diplotene to metaphase I of meiosis). At about 12 hours, the meiotic micronuclei are in metaphase I and display acentric intranuclear spindles with blunt poles and homogenous polar caps; the bivalents have prominent kinetochores. At 16 hours, the somatomicronuclei contain numerous chromatin patches which are possibly subchromosomes, and first nucleoli appear in them. At 16–18 hours, the stage of pronuclei is reached; and other meiotic products start degenerating. The migratory pronuclei show concentration of the chromatin at the centre of the nucleus. At 20, 26, 28 and 34 hours, the fine structure of somatomicronuclei (secondary anlagen) changes little. Their size remains constant (about 5–6 μm). However the nucleoli enlarge at 34 hours. The first division of the synkaryon has protruding poles and no polar caps, unlike meiosis I; though, the nuclear envelope remains intact even at the poles. The synkaryon divisions give rise to new micronuclei and primary macronuclear anlagen.

The primary (meiotic) macronuclear anlagen differentiate in number of 2–4 at 22–24 hours. They are much larger than secondary anlagen (up to 20 μm) and, at early stages of development, their chromatin is so strongly decondensed that the anlagen look “empty”. However later (by 34 hours) loose chromatin patches, small bodies of condensed chromatin and nucleolar primordia appear in them, like in somatomicronuclei, and the primary anlagen at 34 hours show additionally a karyosome-like central condensation of the chromatin.

The extrachromosomal nucleolar apparatus in the macronucleus (Ma) of the ciliate Paramecium putrinum was studied by LM cytochemistry, confocal microscopy and EM. The nucleoli vary in size and number. Three main types of nucleoli can be distinguished: small compact ones, vacuolated and large “composite” nucleoli (CN). The CN are often flattened at the Ma surface, but no blebbing or nucleolar extrusion was observed with EM. The CN are composed of several “nucleolar units” represented by a ring of dense fibro-granular material with an electron dense body in the centre. The nucleolar units are embedded in loose fibro-granular material. Ag-NOR staining and EM data provide evidence for the location of nucleolus organizer regions (NORs) at the CN periphery in the perinucleolar chromatin. Ag-NOR staining reveals a network, connecting extrachromosomal NORs with each other and possibly presenting a skeleton for continuous strands of nucleolar material observed by confocal microscopy during certain stages of cell cycle. “Free” NORs are scattered through the Ma.

Morphological analysis of the micronuclei in 51 stocks of 10 Paramecium species was carried out to examine the diversity of the nuclear morphology in these organisms. Instead of the two general structural types of micronuclei which are well-known in the literature (“caudatum” and “aurelia”), 4 types of nuclei are proposed. They are the “vesicular” type (P. polycaryum, P. arcticum, P. aurelia, P. multimicronucleatum), the “endosomal” type (P. calkinsi, P. woodruffi, P. duboscqui), the “chromosomal” type (P. jenningsi, P. wichtermani) and the “compact” type (3 varieties) — P. caudatum (a), P. bursaria (b) and P. putrinum (c).

The fossil chrysophyte stomatocyst flora of six peat samples from Glacier Ampère, a retreating glacier on Grand Terre, in the subantarctic Kerguelen Archipelago, has been investigated by means of scanning electron microscopy. Thirty-two different stomatocysts were recorded, 27 of which appeared to be previously undescribed. This paper contains the descriptions and illustrations of the new morphotypes. This is the first systematic study of chrysophyte stomatocysts from this subantarctic archipelago following the guidelines of the International Statospore Working Group.