Studies on Coprozoic Ciliates
Authors: Hoare Cecil A. 
Published: June 2009

This paper contains a revision of the morphology and classification of three species of holotrichous ciliates,Lembus pusillus, Cyclidium glaucomaandUronema nigricans(=Uronema marinaDujardin, 1841=Cryptochilum nigricansMaupas, 1883=U. marinaetU. marinumauctorum, 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 betweenU. nigricansand the other species described has led to its transfer from the family Chiliferidae to the family Pleuronemidae.

Cyst formation inL. pusillusis 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-waterU. nigricansadapted itself to pure sea water within 12 days and developed for 12 months in this medium, in which it is still being maintained. The marineU. nigricanswas 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 ofU. nigricansbeing insignificant and transitory, the two forms are regarded as constituting a single species.

The fresh-waterL. pusillusrequired 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-waterC. glaucomato 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 ofC. glaucomaare 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 topH 9·0–10·0, whilst the acidification of the medium beyondpH 5·0 inhibits their growth.

As regards the facility with which these ciliates grew in faecal cultures,Lembusoccupied 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 toUronema, which grew in all the diluted specimens and in one undiluted, whereasCyclidiumwas 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 toCyclidiumorUronema, the ones described by Yakimoffet al.probably representingLembus 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 whichLembuswas found must have been contaminated by this ciliate from outside.