Morphogenetic Studies On Hypotrichous Ciliates During Binary Fission

Hypotrichs is the most complex and highly differentiated among single-celled organisms. Investigations on its cell development, cortical, ciliated organisms, and nuclear apparatus evolution during binary fission are significant to genetic and systematic studies. Accordingly, for a long period of time morphogenesis has always being an important worldwide subject of protozoa. Nevertheless, a truth is that under such circumstances there are still numerous unknown or little-known taxa which need further research and discussion, a great of conflicts, confusion and mistakes are waiting for revision.Taxonomic and morphogenetic studies on Hypotrichous ciliates (Stichotrichids, Urostylids, Oxytrichids, Euplotids) including 15 genera, 20 species mainly sampled from various habitats off the coast of Qingdao are carried out. The investigation referring to the morphogenetic features of genera/species, relationship between representative groups reveals a series of new phenomena and supplies some unknown items, cell development patterns of genera/species level are erected which provide important data for systermatic positions (assignment of family) and relationship between species and genera. Meanwhile, for the internationally long-time uncertain or little-known species, thorough reinvestigations on living morphology, morphometric characteristics as well as infraciliature are executed in order to complete and clarify with redefinitions.The results of the present work can be summarized as follows:(1) In general, ciliates possessing the"8: 5: 5"patterned FVT-cirri were assigned to Oxytrichidae. Nevertheless, the buccal apparatus of the proter in Apogastrostyla rigescens(Kahl, 1932)nov. com. is particularly composed of the anterior portion of the parental AZM and the new membranelles from new oral primordium, together with the"one group type"of dorsal kineties generation, demonstrate the"primitive"characters which are clearly distinct from Oxytrichids. As a result of morphological and morphogenetic comparison with related species, Apogastrostyla nov. gen. is established and doubtfully placed in the family Amphisiellidae. Additionally, we suggest that two"extra"cirri should be derived from the posterior end of right marginal row for no specific anlagen occur. (2) As a rather rare and unique species Leptoamphisiella vermis (Gruber, 1888) Li et al., 2007, is remarkably distinguished for the combination of following characteristics: vermiform and strongly contractile body, differentiated frontal, buccal, and highly developed transverse cirri; two remarkably separated midventral rows; one marginal row on each side of the body; frontoterminal and caudal cirri absent. The revealed morphogenetic features such as the old AZM will be entirely replaced by the new one, midventral complex and transverse cirri derive from FVT-cirral anlagen, the anlagen for both marginal rows and dorsal kineties develop intrakinetally within the parental structures are typically observed in urostylids. Hereby, the new genus Leptoamphisiella Li et al., 2007 which should be close related to Pseudoamphisiella is established and assigned to the family Pseudoamphisiellidae.(3) A new genus, Spiroamphisiella Li, Song & Hu, 2007 is established which can be distinguished by strongly twisted body; one left and more than one right marginal rows, a single ventral row usually segmented; frontal, buccal, pretransverse, transverse and caudal cirri differentiated. In Spiroamphisiella hembergeri Li, Song & Hu, 2007, two key divisional features were observed: i) anterior and posterior segments of ventral row are generated from three cirral anlagen; ii) the right marginal row primordium gives rise to only the row 1, while the row 2 inherits the intact old structure. Accordingly, Spiroamphisiella is classified into Amphisiellidae. Nevertheless, the presence of two rows of right marginal cirri is rather unique among amphisiellids though this structure seems to come from the parental row instead of generating from the primordium. This character indicates likely that the new taxon could represent an isolated position in the phylogeny of the family.(4) The new genus Nothoholosticha Li et al., 2009 is erected based primarily on the absence of frontoterminal cirri during both interphase and divisional process, which distinctly separate it from similar urostylid genera. Because of Nothoholosticha fasciola Li et al., 2009 has Pseudokeronopsis-like body shape, slightly differentiated frontal cirri arranged in two arches like a simple bicorona, midventral complex composed almost entirely of cirral pairs, and the presumed complete replacement of the parental adoral zone of membranelles during cell division, the genus Nothoholosticha is assigned to the family Pseudokeronopsidae.(5) So far Orthoamphisiella marina nov. spec. is the only marine habitated species within the genus. The investigation on its morphogenesis reveals the typical characteristics of"primitive"Stichotrichids. The intrakinetially origin of ventral cirral rows supports Eigner (1997) to classify the genus Orthoamphisiella in the family Orthoamphisiellidae. The expanded diagnosis of Orthoamphisiella Eigner & Foissner, 1991 is suggested as well. (6) The ontogenetic process of Apokeronopsis bergeri Li et al., 2008 corresponds well with its congeners except for the mode of formation of the buccal cirri. In the former, several anterior streaks from FVT-cirral anlagen appear to contribute their last segments to form the row of buccal cirri, which is an unusual feature, while in A. crassa, the buccal cirri are generated from the first FVT-cirral anlage as seen in most other related taxa. The similarities in both morphology and morphogenetic division exhibited by A. crassa and our new species support the conclusion that they belong to the same clearly defined genus within the urostylids.(7) Compared to the congeners, the most particular morphogenetic feature in Pseudoamphisiella elongata Li et al., 2009 is the last FVT-streak contributes two migratory cirri (frontoterminal cirri) which are probably resorbed or positioned in the anterior of the right marginal row. The dissimilarities prove that morphogenetic modes in the genus Pseudoamphisiella are not conservative. In addition, we prefer that in P. alveolata the right marginal anlagen in both dividers occur close together independent of the old structure.(8) Thigmokeronopsis stoecki Shao et al., 2008 shares almost the same divisional process with its congener T. rubra. According to the available data, we can consider that except for the minor difference in the nuclear behavior, the morphgenetic mode among Thigmokeronopsis species is rather stable. Compared to the morphologically related genera (Pseudokeronopsis, Apokeronopsis, Uroleptopsis), Thigmokeronopsis can be distinctly separated by thigmotactic field formed by all of FVT-steaks (not including the first and last few streaks). Therefore, we support the opinion that Apokeronopsis is a transitional form between the Pseudokeronopsinae and Thigmokeronopsis.(9) The morphogenetic process of Metaurostylopsis struederkypkella Shao et al., 2008 is thoroughly investigated. The result represents a typical Metaurostylopsis mode which also occurred in M. marina and M. rubra. Whereas compared with another less morphologically related congener M. sinica, M. struederkypkella shows two conspicuously different points: i) the macronuclear nodules fuse into a branched mass other than a single sausage-like mass; ii) the last two FVT-anlage streaks give rise to a frontoterminal cirral row and a midventral row (vs. only two frontoterminal cirri are formed). Based on the morphogenetic data above, we can conclude that M. struederkypkella, M. marina and M. rubra are closer related to the pseudokeronopsids than M. sinica.(10) The morphogenetic process of Amphisiella annulata (Kahl, 1932) Borror, 1972 is completed with the early to mid-stages. The stomatogenesis in the proter and the origin of cirral anlagen are reported for the first time which contribute the establishment of the morphogenetic mode of Amphisiella. Another two species A. milnei (Kahl, 1932) Horváth, 1950 and A. sinica nov. spec. are also investigated on divisional behavior, and only minor differences appear.(11) 5 FVT-anlagen mode of euplotids is demontrated highly conservative among Euplotes balteatus(Dujardin, 1841)Kahl, 1932, Aspidisca orthopogon Deroux & Tuffrau, 1965, and A. magna Kahl, 1932. The development of dorsal kineties in Certesia quadrinucleata Fabre-Domergue, 1885 is firstly revealed with figures.(12) The fate of the parental oral apparatus in Anteholosticha pulchra (Kahl, 1932) Berger, 2003, A. parawarreni nov. spec. and A. manca (Kahl, 1932) Berger, 2003 is completely replaced by the deeply and independently generated oral primordium in the bucal field which is different from the other two modes (old AZM completely retain, and the"piecing together"mode). This valuable characteristic supports the revision of primary Holosticha assemblage.(13) Cotical and nuclear apparatus evolution of Stylonychia pustulata (Müller, 1786) Ehrenberg, 1835, during binary fission are described in detail. We firstly discover that the second group of the dorsal kineties anlagen actually originate from the anterior segments of right marginal anlagen.(14) Based on morphological and morphogenetic features, several new taxa are established, which includes: 4 new genera: Spiroamphisiella Li, Song & Hu, 2007, Apogastostyla nov. gen., Leptoamphisiella Li et al., 2007, and Nothoholosticha Li et al., 2009. 6 new species: Orthoamphisiella marina nov. spec., Spiroamphisiella hembergeri Li, Song & Hu, 2007, Amphisiella sinica nov. spec., Pseudoamphisiella elongata Li et al., 2009, Anteholosticha parawarreni nov. spec., and Apokeronopsis bergeri Li et al., 2008. 7 new combinations: Apogastrostyla rigescens (Kahl, 1932) nov. com., Leptoamphisiella vermis (Gruber, 1888) Li et al., 2007, Nothoholosticha fasciola (Kahl, 1932) Li et al., 2009, Nothoholosticha longissima Li et al., 2009, Pseudokeronopsis antarctica (Wilbert & Song, 2008) Li et al., 2009, Apogastrostyla enigmatica (Dragesco & Dragesco-Kernéis, 1986) nov. comb., and Apogastrostyla szaboi (Wilbert & Song, 2005) nov. comb. The infraciliature and key divisional stages of Amphisiella milnei (Kahl, 1932) Horváth, 1950, Anteholosticha pulchra (Kahl, 1932) Berger, 2003, Euplotes balteatus(Dujardin, 1841)Kahl, 1932, Aspidisca orthopogon Deroux & Tuffrau, 1965, and Aspidisca magna Kahl, 1932 are revealed for the first time and their neotypes have been deposited. Additionally, detailed morphological descriptions and improved diagnosis are also provided.