The vegetative life cycle, host specificity, morphology, and ultrastructure of a new phagotrophic nanoflagellate are described: Cryothecomonas aestivalis Drebes, Kfihn & Schnepf sp. nov. During summer and autumn it is frequently found in the North Sea phytoplankton feeding on the centric diatom Guinardia delicatula. The flagellate penetrates the diatom cell and phagocyfizes the host cytoplasm by means of a pseudopodium that emerges from the posterior cell pole. The mature trophont gives rise to eight or more biflagellate swarmers which leave the emptied diatom frustule. Transmission electron microscopy revealed a delicate theca surrounding the swarmers. The pseudopodium protrudes through a gap in the theca. The cytostome consists of a membranous labyrinth. The mitochondria are of the tubular type. The two apically inserted flagella are heretodynamic and of unequal length. They are smooth, and their basal bodies are surrounded by satellites and fibrous strands ("transitional fibres" sensu Thomsen et al., 1990). In the trophonts and dividing flagellates the transition region between the flagellum and the basal body ends apically with a massive transitional cylinder instead of distinct microtubules, and is surrounded by a funnel of the theca. The nuclear envelope disintegrates during mitosis. Due to the fine structural details the new flagellate is placed in the genus Cryothecomonas Thomsen et al., a genus of still uncertain position.
We provide brief descriptions with illustrations and document the seasonal occurrence of these species at the two stations. We also discuss investigation methods used for different levels of species recognition, namely Utermo¨hl counts, light microscopical observations of living net-samples as well as scanning electron microscopy of netsamples and isolated cultures. Clonal cultures of some species were established to facilitate the taxonomic investigations and 18S ribosomal DNA sequencing was carried out to complement the morphological studies. A perspective for a routine specieslevel assessment strategy is given.
Life cycles of several species belonging to the marine genera Dissodinium Klebs in Pascher and Pyrocystis Murray ex Haeckel are described. The two known species of Dissodinium, D. pseudolunula Swirl ex Elbr. & Dreb., (= D. lunula auct. nonnull.) and D. pseudocalani (GSnnert) Drebes ex Elb. & Dreb. are ectoparasites of copepod eggs. In this genus, sporogenesis, with obligate sequence from primary cyst to secondary cyst to dinospores, occurs by palintomy. Dissodinium is placed into the order Blastodiniales Schiller and its position in this order is discussed. The asexual life cycle of Pyrocystis spp. represents an alternation between a dominating coccoid stage and a morphologically different transitory reproductive stage. The reproductive bodies may be either athecate aplanospores, athecate uni-or biflagellate planospores or thecate biflagellate planospores. Thecal morphology of thecate planospores resembles those of Gonyaulax Diesing. The occurrence of both, athecate aplanospores and thecate planospores in the same species, is discussed. Pyrocystis is regarded as belonging to the order Pyrocystales Apstein. The possible derivation from the Gonyaulacaceae Lindemann is suggested. In addition, the genera Dissodinium and Pyrocystis are redefined. A description of D. pseudolunula as well as a list of synonyms and references for detailed descriptions of P. lunula (Schiitt) Schiltt, not including D. pseudolunula, is given.
All members of the dinophyte Paulsenella are ectoparasites on marine planktonic diatoms. At present three species are known, two of which are described here for the first time. The taxonomy of the type species, P. chaetoceratis, is paid critical attention. The species are clearly distinguished by their host specificity and additionally by differences in morphology, especially of the trophonts. Using clonal cultures the life cycles of the three species are compared. The vegetative development may be interrupted by formation of temporary and resting cysts. In ageing cultures, stages with nuclear cyclosis occur, believed to indicate meiosis. In P. vonstoschii, the meiospores are capable of developing into resting cysts. As yet, knowledge on sexual reproduction is still incomplete.
KURZFASSUNG: Zur Entwicklungsgeschichte der marinen Planktondiatomee Stephanopyxis palmeriana. Im Friihjahr 1964 wurde die zentrlsche Planktondlatomee Stephanopyxis patmeriana (GREy.) G~uNow -eine aus japanischen Gew~issern stammende Warmwasserform und unserer S. tuttis sehr nahe verwandt -in Kultur genommen. Schon nach knrzer Zeit war es m~Sglich, den gesamten Formwechsel dieser Alge in seinen Grundziigen kennenzulernen. Mit Hilfe yon Wasserimmersionen konnten in dlrekter Lebendbeobachtung Zellteilung, Meiosis, Befruchtung und Auxosporenbildung mit ihren metagamen Mitosen sowie die BiIdung und Keimung der Dauersporen studiert werden. Morphologisch stimmt der Formwechsel mit dem yon S. tuttis (v. SxoscH & D~E~ES 1964) iiberein; in der Abh~ingigkeit yon Umweltfaktoren bestehen jedoch Unterschiede. So werden Dauersporen bei dieser zwischen 19 und 156 ~ Zellbreite (= Transversaldnrchmesser) vegetativ existierenden AIge nnr von schmalen, unter 90 ~ breiten Zellen in Gegenwart yon Phosphatmangel (sp~rlich manchmal auch bei Nitratmangel) differenziert. Eine Temperatur yon 120 C wirkt dabel sehr begiinstigend. Die Keimung der Dauersporen setzt nach Beseitigung des Phosphatmangels ein. Zur Sexualisierung sind nut unter 60 lz breite Zellen f~ihlg; sle findet start nach sprunghafier Stelgerung der Beleuchtungssfiirke (yon 400 auf 4000 Lux) sowie einer TemperaturerhShung yon 150 auf 2i o C. Wegen der Dickschallgkeit bereitet die Anderung der Zellgr6fle auf k[instlichem Wege durch SiO2-Mangel mit nachfoIgender Schalenregeneration elnige Schwierigkeitem Diese Manipnlatlonen sind jedoch notwendig, wenn ein Klon ohne Ver~inderung seines Idlotypus fiber die Auxospore ffir unbegrenzte Dauer zur Verfiigung stehen soll.1 The studies were carried out in the Botanical Institute of the University, Marburg.
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