Uronema Nigricans Research Articles

Morphological Redescription and SSU rDNA-based Phylogeny of Two Freshwater Ciliates, Uronema nigricans and Lembadion lucens (Ciliophora, Oligohymenophorea), with Discussion on the Taxonomic Status of Uronemita sinensis

The morphology and phylogeny of two poorly known species, Uronema nigricans (Muller, 1786) Florentin, 1901 and Lembadion lucens (Maskell, 1887) Kahl, 1931, were respectively collected from a eutrophic freshwater river in Shenzhen and an oligotrophic lake in Zhanjiang (both in southern China) and investigated using standard taxonomic methods. The sampled population of Uronema nigricans was characterized by a cell size of 30–40 μm × 12–20 μm in vivo, an elongated elliptical outline with a prominent apical plate, and 13–15 somatic kineties. The sampled population of Lembadion lucens was characterized by a cell size of 45–80 μm × 20–50 μm in vivo, 25–35 somatic kineties, five or six caudal kinetosomes with cilia about 20 μm in length, and a single right-positioned contractile vacuole. The small subunit ribosomal RNA gene (SSU rDNA) of these species was sequenced and compared with those of their congeners to reveal nucleotide differences. The phylogenetic trees showed that the Shenzhen population of Uronema nigricans clusters with two other sequences under the name of “Uronema nigricans” (which are possibly misidentified) and then groups with Uronemita sinensis (Pan et al., 2013) Liu et al., 2016 with full support. Phylogenetic analyses indicated that genus Lembadion is monophyletic with full support provided by both Bayesian inference and maximum likelihood algorithms. Based on analyses of morphological and sequence data, Uronemita sinensis may represent a new genus between Uronema and Uronemita.

Molecular characterisation of Miamiensis avidus (Ciliophora: Scuticociliata) from ranched Southern bluefin tuna, Thunnus maccoyii off Port Lincoln, South Australia

Scuticociliates are opportunistic protozoan pathogens present in a wide range of teleost hosts. Uronema spp. and Miamiensis spp. are the two most common genera recorded from scuticociliatosis cases in farmed and ornamental fish. Southern bluefin tuna (Thunnus maccoyii) (SBT) ranching is a high value aquaculture sector, situated off Port Lincoln, South Australia. Uronema nigricans has been previously associated with SBT swimmer mortality syndrome and was considered to be the causative agent. We conducted the first molecular characterisation of swimmer syndrome agent from affected SBT. Comparison of SSU rDNA and mitochondrial cytochrome c oxidase 1 sequences from the cerebrospinal fluid from SBT affected by swimmer syndrome and Uronema marinum samples, and phylogenetic analyses identified the scuticociliate present in SBT samples as Miamiensis avidus. Bayesian Inference analyses of both partial gene sequences of the Port Lincoln isolates form a clade with known M. avidus to the exclusion of Uronema spp. This shows that M. avidus is associated with swimmer syndrome and is present in the environment around SBT leases. Based on our molecular data, there is no evidence of Uronema spp. presence in the infected SBT. This is the first time M. avidus has been documented in Australia.

Diversity of ciliates in small rivers in vicinity of Khabarovsk and in southern Sakhalin Island

Data on species composition of ciliates in the small rivers at Khabarovsk and in southern Sakhalin Island are presented. Modified method of sampling was applied with using of samplers and “glass fouling” on the shallows of the rivers. More than 230 samples were collected in the small rivers at Khabarovsk and about 200 samples in the southern Sakhalin. Species composition of the ciliates was determined immediately after the sampling and repeatedly on nutrient media. In total, 86 species of ciliates are identified, mostly belonged to the classes Oligohymenophorea and Spirotrichea. Six eurybionts were found: Coleps hirtus, Paramecium caudatum, Dexiostoma campylum, Colpidium colpoda, Uronema nigricans, and Vorticella convallaria сomplex . The classes Armophorea and Phyllopharyngea were more diverse by species in the area at Khabarovsk but the class Spirotrichea - in southern Sakhalin. In general, faunas of ciliates in two surveyed regions are similar. The highest inter-regional similarity of the species composition is registered between the rivers at Khabarovsk and the Susuya River in Sakhalin (25-33 %, by Jackaroo) that is probably associated with a heightened level of pollution in the Susuya. Most of the species adapt to habitat rapidly, so they are found in different environments: among benthos, plankton, periphyton. Some patterns of the ciliocommunities are discussed.

Horizontal Distribution of Psammonic Ciliates in Two Lakes of Different Trophic Status: Relationship to Physical and Chemical Parameters

Horizontal Distribution of Psammonic Ciliates in Two Lakes of Different Trophic Status: Relationship to Physical and Chemical ParametersThe aims of this study were to identify the taxonomic diversity and abundance of psammonic ciliate communities in mesotrophic and eutrophic lakes (Łęczna-Włodawa Lakeland, eastern Poland). The effect of selected physical and chemical water parameters on ciliates community was also analysed. Psammon samples were collected during three seasons: spring, summer and autumn of 2010. In each lake, in the psammolittoral, samples were collected in the euarenal, higroarenal, and hydroarenal zones. A total of 53 ciliate taxa were recorded. The highest value of the Shannon-Weaver index was recorded in summer in eutrophic lake (2.79). At the same time in mesotrophic lake, a lower value of the index was determined (0.79). The mean numbers of ciliates ranged from 516 ind.cm-3in the eutrophic lake to 191 ind. cm-3in the mesotrophic lake. In eutrophic lake, the highest number of ciliates was recorded in the euarenal (649 ind. cm-3), and the lowest in the higroarenal (425 ind. cm-3). In the mesotrophic lake, the highest average numbers were determined in the higroarenal (235 ind. cm-3), and the lowest in the hydroarenal (155 ind. cm-3). Irrespective of the lake trophy, Hymenostomata (Paramecium sp., Glaucoma sp., Uronema nigricans) occurred in the highest numbers (from 13 to 95%). The results demonstrated that N-NH4, P-PO4and TOC can strongly regulate the abundance and taxonomic composition of ciliates. The strongest correlations between numbers of ciliates and physical and chemical water parameters were observed in the higro- and hydroarenal zones of the eutrophic lake.

Factors Affecting Preference Responses of the Freshwater Ciliate Uronema nigricans to Bacterial Prey

To enhance our understanding of the factors affecting feeding selectivity of bacterivorous protists in aquatic systems, we examined the preference responses of the freshwater ciliate Uronema nigricans towards three bacterial prey taxa, Pseudomonas luteola, Serratia rubidaea, and Aeromonas hydrophila. Potential factors influencing the predator-prey contact rate included the previous feeding history of the ciliate and physiological state of bacteria. Preference indexes were obtained from multiple-choice mazes in which ciliates moved preferentially towards alternative bacteria or the prey species on which they had been feeding. Uronema nigricans showed differential attraction towards the offered prey types, and these preferences varied as a function of the ciliate feeding history: U. nigricans growing on P. luteola showed lower preference responses towards the offered bacteria than U. nigricans growing on S. rubidaea. The bacteria in stationary phase elicited a higher degree of attraction than bacteria in exponential phase, probably due to a higher concentration of carbohydrates in the former. Therefore, this protist will preferentially swim towards bacteria in stationary growth phase, although the degree of this response will be affected by the recent feeding history of the ciliate.

Ciliates and their picophytoplankton-feeding activity in a high-altitude warm-monomictic saline lake

The impact of feeding on autotrophic picoplankton (APP) on the ciliate composition of the assemblage was surveyed monthly along a depth gradient in the maar crater, athalassohaline, warm monomictic Lake Alchichica (Puebla, Mexico) from June 2003 to December 2005. Numbers of APP were evaluated from their autofluorescence. DAPI staining and the Fluorescently Labeled Bacteria technique were employed to count ciliates and estimate their feeding rates. A total of 38 taxa of ciliates have been identified using Quantitative Protargol Staining. Peritrichs followed by minute spirotrichs (particularly Halteria grandinella) often numerically dominated the ciliate assemblage and emerged as the most efficient APP feeders. A maximum of 54 ciliate cells ml −1 was observed in the surface layer at the end of the mixing period, during the development of diatoms ( Cyclotella alchichicana), the cyanobacterial bloom ( Nodularia sp.) and its decay. Vorticellids ( Pelagovorticella natans, Vorticella sp.) had the highest APP uptake (median 130 APP cil −1 h −1). Mixotrophic Euplotes cf. daidaleos were important APP grazers near the oxycline. Scuticociliates ( Cyclidium glaucoma, Uronema nigricans and an anaerobic cf. Isocyclidium globossum), were numerically dominant within the hypolimnetic assemblages and did not ingest APP. Generally, APP were not an important food source for the majority of the ciliate assemblage, being positively selected by a few species during the APP decay in aerobic and microaerobic conditions.

A parasite survey of farmed Southern bluefin tuna, Thunnus maccoyii (Castelnau)

Farmed Southern bluefin tuna (SBT) were examined for parasites. Samples of harvest fish, mortalities and some fish showing clinical signs of disease were investigated. Targeted screening was conducted for a scuticociliate, Uronema nigricans, the myxosporean Kudoa sp. and a sanguinicolid digenean, Cardicola forsteri. General parasitological investigation revealed a diverse parasite community of didymozoid digeneans, two species of copepods, a polyopisthocotylean monogenean and larval cestodes. Targeted screening for U. nigricans exposed a low prevalence, most probably due to a lack of sensitivity in the test method. Few of the parasites examined pose a risk to the health of farmed SBT.

Effects of bacterivorous ciliated protozoans on degradation efficiency of a petrochemical activated sludge process

The aim of this work was to adapt protozoans to a saline and crude-oil contaminated petrochemical sewage. Wild type protozoans were isolated from different marine locations and from a municipal-refinery mixed sewage treatment plant. In batch culture the micro-organisms were adapted by slowly increasing concentrations of sodium chloride and hydrocarbons. No wild type strain survived in the saline sewage. Using selected type strains of protozoans as inocula, Cohnilembus rheniformis and Uronema marinum were found to adopt to the brine. In a 20 l-batch culture U. marinum grow up to a number of 14.000 cells·ml −1. Since the yield was recognized to be to small for further scale-up, additional experiments were done in continuous culture. In a lab-scale 2-step continuous culture, inoculated with natural activated sludge mixed populations of protozoans, one single species of a ciliated protozoan could be enriched and identified as Uronema nigricans. The effluent turbidity, measured as optical density (OD 600), of the lab-scale activated sludge plant decreased dependent on the increase of U. nigricans count. In addition, chemical oxygen demand degradation efficiency was found to be 45.8%, compared to 35.4% in activated sludge mixed cultures missing protozoans.

Environmental factors and chemical agents affecting the growth of the pathogenic marine ciliate Uronema nigricans.

The scuticociliate Uronema nigricans is an opportunistically parasitic marine ciliate known to cause disease in some aquacultural environments with epizootics documented from marine larval rearing systems, marine aquaria and in southern bluefin tuna Thunnus macoyii growout enclosures. This study examined growth responses of laboratory cultures of the ciliate and prey bacteria to variations in temperature and salinity, and the efficacy of potential chemotherapeutants for control of U. nigricans infections. Differences in ciliate growth responses were marginal at temperatures of 10 to 25 degrees C and at salinities between 15 and 35 ppt, though 3.5 ppt or less was lethal. Ciliates were found to be sensitive to fluctuations in bacterial densities, which may be a factor in the seasonal occurrence of the ciliate-related disease in tuna. Commonly used chemotherapeutants such as formalin, malachite green and hydrogen peroxide were all effective against the ciliate during in vitro trials.

Seasonal dynamics and vertical distribution of planktonic ciliates and their relationship to microbial food resources in the oligomesotrophic Lake Pavin

The planktonic ciliated protozoa and their potential prey (bacteria, autotrophic picoplankton, flagellates, algae) in Lake Pavin (Massif central of France) were investigated during the period of April to December, 1992. Ciliate abundance varied from 300 to 24,200 cells/l. Peak densities were observed during mixis for all sampling depths and in May-June in the cold aerobic hypolimnion. During the rest of the year, the species composition varied greatly with depth and season. Small algivorous prostomatids and large mixotrophic oligotrichs were most abundant in the euphotic zone during summer. Small filter-feeders were present at each depth throughout the study whereas haptorids and large size taxa were restricted to 15 m depth during spring and autumn. The highest density of ciliates occurred in the deep (40 m) cold aerobic hypolimnion due to the major spring development of the scuticociliate Uronema nigricans. This species seems to be adapted to cold and dilute freshwater habitats. Evidence for a major impact of availability and diversity of appropriate food in determining ciliate composition at different seasons and depths are given.

Ciliated protozoa of a geothermal sulphur spring

The species richness and the dynamics of the ciliatecommunitieswere studied at three stations along a streamlet formed bywaterdischarged from a geothermal sulphur spring. Altogether, 73specieswere identified. Ciliate coenoses were composed primarily offreshwater forms, but they were numerically dominated byeuryhalinespecies. The great fluctuation in both number of species andindividuals observed along the streamlet were due to vigorouschemical changes in the physico-chemical characteristics ofthewater. These changes were caused mainly by the sulphide andsaltgradient observed along the water course. The maximum value ofsulphide was observed in August with 391 µM l−1, andthehighest conductivity value was observed in April with 18 mScm−1. The most characteristic and abundant species weresmall-sized bacterivorous scuticociliates which have a rapidecological adaptability and whose tolerance limits toenvironmentalchanges are wide. Bacterivorous scuticociliates such as Cyclidium citrullus, C. glaucoma, Cinetochilummargaritaceum, and Uronema nigricans were numericallydominant when the thermal water contained the highestconcentrationof sulphide. The diversity index values changed sharply intimeboth inside and among sampling stations, indicating unstablecommunities which depended on highly fluctuatingconditions.

Fatal encephalitis due to the scuticociliate Uronema nigricans in sea-caged, southern bluefin tuna Thunnus maccoyii

DAO Diseases of Aquatic Organisms Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials DAO 30:17-25 (1997) - doi:10.3354/dao030017 Fatal encephalitis due to the scuticociliate Uronema nigricans in sea-caged, southern bluefin tuna Thunnus maccoyii Munday BL, O'Donoghue PJ, Watts M, Rough K, Hawkesford T A syndrome characterized by atypical swimming behaviour followed by rapid death was first reported in captive southern bluefin tuna Thunnus maccoyii (Castelnau) in the winter of 1993. The cause of this behaviour was found to be a parasitic encephalitis due to the scuticociliate Uronemanigricans (Mueller). Based on parasitological and histological findings, it is proposed that the parasites initially colonise the olfactory rosettes and then ascend the olfactory nerves to eventually invade the brain. Possible epidemiological factors involved in the pathogenesis of the disease include water temperature (<18°C) and the immune status of the fish. Southern bluefin tuna · Thunnus maccoyii · Scuticociliate · Uronema nigricans ·Encephalitis · Neuritis Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in DAO Vol. 30, No. 1. Publication date: July 24, 1997 Print ISSN:0177-5103; Online ISSN:1616-1580 Copyright © 1997 Inter-Research.

Capability of ciliated protozoa as indicators of effluent quality in activated sludge plants

The aim of this study is to determine the relationship between the ciliate populations density and effluent quality in activated sludge plants. A total of 231 samples taken at three activated sludge plants were analyzed over a three year period. Seven physico-chemical parameters were examined and protozoa (in particular ciliate protozoa) and small metazoa were counted by means of optical microscopy. Effluent quality was determined from BOD 5 and suspended solids concentration. For data analysis the species were classified in ranges in terms of abundance. Mean and standard deviation of effluents BOD 5 and SS were calculated for each range. It was found that as the abundance of each species population increased, both BOD 5 and suspended solids from effluents tended to a particular range of values (the optimal range) whereas the standard deviation diminished. Thus the higher the ciliate species population density, the better the capability of the species as an indicator, which is something reflected in the standard deviation. This capability of ciliated protozoa to act as indicators of effluent quality will also be limited by the other factors influencing the presence of species. It was observed that the correlation coefficients between ciliates and effluent quality depend on the range of physico-chemical values studied, i.e. whether they are superior or inferior to the “optimal range”. The values of each species' BOD 5 optimal range varied from 4 mg/l to 18 ppm, suggesting that ciliates are good indicators between 4 and 18 ppm in activated sludge plants. In all cases observed, less common species such as Acineta tuberosa, Euplotes sp. and Zoothamnium sp. were indicators of high effluent quality. By contrast, the species that reach the highest densities and are the most common, such as Uronema nigricans, Vorticella microstoma and Opercularia coarctata, indicated lower effluent quality.

The Kinetic and Analytical Complexities of the DNA Genomes of Certain Marine and Fresh‐Water Ciliates1

ABSTRACTWe investigated the macronuclear DNA genomes of several marine and fresh‐water ciliates. The marine forms studied were: Uronema nigricans, Parauronema virginianum, Parauronema acutum, and two strains of Miamiensis avidus; the fresh‐water ciliates included: Tetrahymena pyriformis, Paramecium octaurelia, and P. caudatum. The organisms were cultured axenically and the DNA extracted from isolated and purified macronuclear preparations. Reassociation rate constants of purified DNA preparations used to calculate kinetic complexity were determined both optically and by hydroxyapatite chromatography. Analytical complexity was determined chemically. Ciliate macronuclear DNA appeared to reassociate as a single unique sequence, except for a small fraction (4% of the total DNA) that was repetitive and renatured rapidly. Values for the kinetic complexities of macronuclear DNA in these forms varied over a relatively narrow range, from 1.5 to 3.8 times 1010 daltons, and were only 7–15x larger than that of the bacterium Escherichia coli. On the other hand, values for analytical complexities of macronuclear DNA of marine and fresh‐water ciliates varied over two orders of magnitude and were related to the size of the animals. It is suggested that ploidy levels of macronuclear DNA in these ciliates may represent a functionally permanent amplification of the genome.

Transfer of mercury through a marine microbial food web

Transfer and accumulation of mercury was observed to occur in a three-component estuarine food web comprising bacteria, ciliated protozoa, and copepods. Results of experiments designed to test trophic interactions revealed significant feeding of each predator on its prey. To initiate transfer and accumulation, a Vibrio sp. and Pseudomonas sp. were cultured separately in media amended with 0.2–1.0 ppm mercury, in the form of 203HgCl 2. Both bacterial species readily accumulated mercury, with the Vibrio sp. accumulating more mercury at low initial concentrations than the Pseudomonas sp., even though the Vibrio sp. was less tolerant to elevated concentrations of mercury. Washed suspensions of labelled bacteria were fed to the ciliate, Uronema nigricans, and mercury transfer was monitored by liquid scintillation counting. Phase microscopy of samples confirmed the presence of large numbers of food vacuoles within the ciliates, which was correlated with an increase in radioactivity of the ciliate fraction. The mercury concentration in protozoa was observed to be greater than that of the individual bacteria on which they fed, demonstrating magnification of mercury in the higher trophic level. The amount of mercury taken up by ciliates was dependent upon the number of mercury-laden bacteria available as food. When labelled ciliates were fed to the copepod, Eurytemora affinis, mercury concentration in the copepods was less than that of the ciliates, although greater than the initial concentration in the bacterial medium, indicating magnification above background level in the copepod. Sterile kaolinite clay to which 203HgCl 2 was added, when fed to copepods, resulted in mercury transfer and retention in the copepods, indicating that, in addition to biologically-mediated uptake, non-biological transfer to, and accumulation in, copepods also occurs.

Ciliates of solar lake on the red sea shore

Solar Lake, about 20 km south of Elat, is a mesothermal, monomictic lake heated heliothermally. Its turnover occurs in the summer months, during July and August. During the rest of the year the lake is layered. The epilimnion is about 1 m thick, the metalimnion lying at a depth of 90–120 cm. The hypolimnion is anaerobic and can be heated to a maximum of 56.6 °C. The water is 4 to 6 m deep, depending on the season. During the stagnation period in the spring of 1978 qualitative measurements were made of the ciliate fauna in the lake. Samples were taken from the pelagic and benthic regions, from the shore to the middle of the lake. No ciliates were found in the entire pelagic region. All the 16 species found in the benthic region were in the zone of layered algal mats (Zone IV) and in the “pinacle algal mat” (Zone III) ( Krumbein and Cohen 1974). These two zones extend to the lower boundary of the epilimnion. In the algal mats of the deeper Zones II and I no ciliates were found. This result is apparently due to the high water temperatures prevailing at these depths and to the anaerobic conditions, for adequate food (algae and bacteria) is present. Stephanopogon apogon, Uronema nigricans, Uronema filificum, Parauronema virginianum, Pseudocohnilembus marinus, Halteria grandinella, Euplotes rariseta and Uronychia transfuga are bacteriophagous; the alga-eaters include Frontonia marina, Condylostoma reichi n. spec, Condylostoma patulum, Tachysoma spec, and Holosticha diademata. Enchelyodon trepida and Litonotus lamella are predators on other ciliates. One ecological characteristic shared by the species found is their high salinity tolerance. L. lamella, U. nigricans, H. grandinella and H. diademata are known to live in fresh water and in the ocean, and the main range of the other species covers a great variety of marine biotopes. The infraciliature of all the ciliates was studied with AgNO 3 (by the method of Chatton-Lwoff ) or protargol ( Wilbert ). Condylostoma reichi (Fig. 7) is new to science. New species and genus characteristics of Uronychia transfuga (Fig. 10, Fig. 11) are described, on the basis of infraciliature and morphogenetic stages.

A Study of Feeding Responses to Bacterial Prey by Estuarine Ciliates

BERK, S. G., COLWELL, R. R. & SMALL, E. B. 1976. A study of feeding responses to bacterial prey by estuarine ciliates. Trans. Amer. Micros. Soc., 95: 514-520. Growth of two estuarine ciliates, Uronema nigricans and Potomacus pottsi, was inhibited when the bacterial food source was at a population level of < 106-107 cells/ml. Feeding rates of Uronema varied with the type and population density of bacteria. The feeding rate of Uronema was greater when a Vibrio sp. served as food source compared with a Bacillus sp. Significant differences noted in the ciliate population levels were related to the strains used as food source. As predators of bacteria, ciliated protozoa can be significant in the ecology of aquatic environments. Marine protozoa grazing on bacteria are important agents in the regeneration of nutrients (Johannes, 1965). Protozoa, plentiful in activated sludge systems, are responsible for the quality of the sewage effluent since they graze on coliform bacteria associated with the effluent, thereby removing a high percentage of these bacteria (Curds & Cockburn, 1968). In turn, protozoa serve as prey for organisms of higher trophic levels, thus constituting a link in aquatic food chains. It has been noted by Hamilton & Preslan (1969) that marine copepods feed on certain of the marine ciliates. In the present study, it has been observed that in estuarine water samples brought into the laboratory, copepod larvae attack and ingest Pleuronema. The feeding responses of ciliates to their estuarine bacterial prey, therefore, may have important consequences in the food web. Few investigations have been conducted on the feeding habits of estuarine bactivorous protozoa (Fenchel, 1968a,b; Hamilton & Preslan, 1969), although more observations have been made on fresh-water organisms (Barna & Weis, 1973; Curds & Cockburn, 1968; Hairston et al., 1968; Laybourn & Stewart, 1975; Proper & Carver, 1966; Seto & Tazaki, 1971). The present study examines some aspects of feeding responses of estuarine ciliates to their bacterial prey.

A Redescription of Uronema nigricans*

SYNOPSIS. Uronema nigricans, a hymenostome ciliate, is redescribed by modern technics. Anatomic studies were made on 4 strains treated primarily with the Chatton‐Lwoff silver impregnation technic. Particular attention was given to the buccal apparatus and its importance to generic assignment in the order Hymenostomatida.

Studies on Coprozoic Ciliates

This paper contains a revision of the morphology and classification of three species of holotrichous ciliates, Lembus pusillus, Cyclidium glaucoma and Uronema nigricans (=Uronema marina Dujardin, 1841=Cryptochilum nigricans Maupas, 1883=U. marina et U. marinum auctorum, pro parte), together with various observations on their biology. The revised data on these species are summarised in the diagnoses preceding their description.The close resemblance between U. nigricans and the other species described has led to its transfer from the family Chiliferidae to the family Pleuronemidae.Cyst formation in L. pusillus is described for the first time. The cysts, when fully formed, are provided with a double-layered wall, to which the body of the ciliate is more or less closely adherent. When preserved in dry condition, the cysts retain the same structure and are able to hatch after several months. Excystation is brought about by active rupture of the cyst-wall on the part of the ciliate. The primary cyst does not, however, afford adequate protection to the ciliate in a fluid medium. After remaining in the latter about three weeks, the animal secretes a cyst of the second order, in which it remains viable some time longer, but if left in the fluid, the ciliate ultimately dies, gradually breaking up into a number of granules.In order to establish the relationship of the marine and fresh-water forms of the same species, experiments on their acclimatisation to the opposite environment were conducted. The fresh-water U. nigricans adapted itself to pure sea water within 12 days and developed for 12 months in this medium, in which it is still being maintained. The marine U. nigricans was gradually transferred to fresh water, in which it was kept for 60 days. Observations on the morphological changes undergone by this ciliate in the course of acclimatisation show that the fresh-water forms living in sea water gradually acquire the habitus of the marine ones, and that the latter undergo the reverse change in fresh water. The characters distinguishing the two strains of U. nigricans being insignificant and transitory, the two forms are regarded as constituting a single species.The fresh-water L. pusillus required eight days for acclimatisation to sea water, in which it was maintained for 163 days without exhibiting any morphological changes.Attempts to acclimatise the fresh-water C. glaucoma to pure sea water failed, but in 50 per cent, sea water it grew for 130 days. The morphological and biological differences between the fresh-water and marine strains of C. glaucoma are probably sufficient for them to be regarded as sub-species or races.Experiments were conducted on the cultivation of these ciliates in faecal matter from normal and diseased human subjects, and varying widely in consistency. Tests on the influence of the reaction of the medium upon the growth of the ciliates showed that they prefer a slightly alkaline medium (pH 7·4–8·0), but are able to tolerate an increase of alkalinity up to pH 9·0–10·0, whilst the acidification of the medium beyond pH 5·0 inhibits their growth.As regards the facility with which these ciliates grew in faecal cultures, Lembus occupied the first place, having developed in the majority (64 per cent.) of samples of pure (i.e. undiluted) faeces, and in all those slightly diluted with water. The second place belongs to Uronema, which grew in all the diluted specimens and in one undiluted, whereas Cyclidium was unable to grow in pure faeces, but developed in about half of the diluted samples. All these ciliates were successfully cultivated in suspensions of human and animal faeces.The coprozoic habits of the ciliates in question are compared with the records for “Uronema caudatum,” comprising a number of ciliates described by some authors as human intestinal parasites. It is shown that the conditions under which these ciliates were observed indicate that they were coprozoic forms that had contaminated the material examined. Though described under the name “U. caudatum” these ciliates represent at least two distinct genera, those recorded by Martini being similar to Cyclidium or Uronema, the ones described by Yakimoff et al. probably representing Lembus pusillus.The last-named ciliarte having been originally found in a sample of canine faeces, experiments were carried out with the view of ascertaining its origin. It was demonstrated that the ciliate was unable to withstand incubation at 37°C. for 24 hours, and, when fed to mice in the form of cysts, did not survive the passage through their intestine. These facts indicate that the faeces in which Lembus was found must have been contaminated by this ciliate from outside.