Tuatara: Volume 5, Issue 3, March 1955
Some Freshwater Ciliates from the Wellington Area Including Eleven Species Recorded from N.Z. for The First Time
Some Freshwater Ciliates from the Wellington Area Including Eleven Species Recorded from N.Z. for The First Time
In the last century when microscopy was a popular hobby, as in the days when Kirk, Maskell and their associates formed a Microscopical Section of the Wellington Philosophical Institute, the ciliates were much studied and admired for their size, varied and often beautiful form, and activity. None are really small. The ordinary powers of the microscope are adequate for the study of their behaviour, of the often strikingly attractive detail of their structure, and of the cilia and ciliary mechanisms responsible for locomotion and feeding in most species. Observations are best made on the live animal, or at best with simple staining techniques, so that an expensive laboratory is not needed except for the most advanced work. They were, and are, readily obtainable and can be easily cultured. Hence their former popularity, which it is hoped this survey will assist to restore, since it presents not only adequate data for the recognition of many common species, but in adding eleven species (marked with an asterisk in the list) to the 123 species previously known from this country, it shows that the study of these animals is still scientifically profitable in this country.
The species included in the present account have been taken from a variety of habitats, permanent ponds and pools, bush tarns, slow-running streams, aquarium tanks, etc. Ciliates have quite marked habitat preferences, and it is accordingly necessary to examine a range of habitats if any number of species are sought. In fact, the preference is so strong in many, that species found close to the surface may be different from those page 88 in the mud at the bottom of the habitat, and for this reason all levels and parts of the habitat should be examined even to the extent of taking washings from plants, submerged wood, and stones. Only small samples of water and washings are necessary; 50 to 100 cc. is quite an adequate sample to take to the laboratory for culturing as described below. Culturing will usually yield such animals as Vorticella and Paramecium, which are so freely used for laboratory studies; but in addition other, and often equally useful, animals such as Spirostomum and Stylonychia will be found.
Bary (1950) has reviewed the knowledge of our freshwater ciliates, and in this came to the conclusion that the species found here are essentially cosmopolitan. Thus the New Zealand microscopist has the advantage of a world-wide literature, and is not faced with the study of a group of animals peculiar to this country and difficult through their systematic novelty. The study of Protozoa is now well organised, and the microscopist who commences work in this group will find that the literature listed in this paper will provide an adequate guidance through most systematic problems. In fact, this and many other aspects of the ciliates make them most suitable for researches in the home or in small or poorly-equipped laboratories.
Culturing is simple, a convenience and an advantage, since by culturing species can be kept alive in the laboratory over long periods and when wild stock is cultured different species ‘bloom’ at different times. If a new culture (subculture) is started when a species ‘blooms’ and is dominant in the original culture, it is not difficult to establish a pure culture of that one species which can be then repeatedly cultured, and so kept alive for intimate detailed study of its structure and life-history. Kirby (1950) gives an extensive account of the many different techniques which can be used in the study of ciliates and other Protozoa; but the following will prove adequate for most free-living freshwater ciliates.
All ciliates are best studied as live material which will yield data adequate for the diagnosis of nearly every species ordinarily encountered. This can be done with the ordinary wet-mount preparation on a 3 in. × 1 in. slide with a coverslip, but a ‘hanging-drop’ mount will often keep a single specimen alive for one or more days and so allow prolonged study. A glass ring ¼ in. or less in thickness is cut from ½ in. internal diameter glass tubing and ground on a carborundum stone to give parallel sides. This ring is sealed with vaseline to a microscope slide, and the upper surface lightly smeared with vaseline. A small drop of water with a specimen in it is placed on a coverslip. The slide is inverted, the edge of the ring touched lightly on the coverslip with the drop centered in the ring so that the coverslip adheres to the ring, and the whole gently but quickly turned over so that the drop of water now hangs from the centre of the coverslip. This preparation is examined in the usual way. The drop must be as small as practical, or the specimen cannot be kept in focus under high power.page 89
If a preparation is made with very dilute Indian ink in water, the action of cilia, the manner of feeding and the formation of food vacuoles can be very clearly observed. While it is not essential to slow most species for observation, and many will slow down on a slide after some minutes, the following methods can be used when necessary.
Gelatine Solution: Make a 3% solution of gelatine with distilled water. One drop of this stock solution is placed on a slide and warmed slightly. Add to this one drop of culture fluid. This gives a gelatine concentration of approximately 1.5% which slows most ciliates successfully. Some of the more delicate species may survive only for a short period.
Copper Sulphate: One drop of 1% copper sulphate in one drop of culture, giving a solution of 0.5%. Species were slowly killed with little change in form until death, when autolysis occurred. An 0.2% solution gives a longer period of immobility before death.
Urethane: This crystalline narcotic was found useful in immobilising species such as Coleps and Stylonychia. Place a crystal of urethane to one side of the coverslip in contact with the culture medium. Distortion occurs if too high a concentration of the narcotic is used, but if in sufficient dilution, movement is retarded.
Isopropyl Alcohol: Used as the vapour (Bary's modification of Bills'  method). Expose a drop of culture fluid on a slide to the fumes of a 2 to 5% solution of the alcohol for several minutes. Slows down individuals for a short period before they explode. This is recommended by Bary and was most useful for species of Paramecium and Halteria grandinella.
Cooling: Place slide on block of ice for several minutes. A drop of acetic acid on the coverslip eliminates condensation.
Nuclei are well stained with dilute methyl green (methyl green 1.0 grm., glacial acetic acid 5 ml., aq. dist. 95 ml.). Permanent preparations are not easy since it is difficult to fasten specimens to a slide, but if a smear is made and allowed to nearly dry and is then gently immersed in Schaudinn's fixative, it can be stained with Heidenhain's or Ehrlich's hæmatoxylin and mounted, after dehydration, in Canada Balsam (see Tuatara Vol. V , p. 14).
Cultures can be held in 1 in. test-tubes, 4 in. × 1 in. vials, or 100 cc. conical flasks. These are plugged with cotton wool. The object in preparing a culture is to supply an adequate stock of bacteria as food, and an environment in which the oxygen content of the water can be controlled. If a conical flask is nearly filled, the surface area is smaller than in a partly-filled flask, and as a result the former has a slower oxygen uptake than the latter and so is suitable for many mud-inhabiting species, while the latter can be used for surface-dwelling species whose oxygen requirement is higher. Since the nutrient requirements of the bacteria are page 90 gradually used up in a culture, transfer to a fresh culture is necessary after a period of time; but the fresh culture must be prepared a week before the transfer to permit growth of bacteria. In the case of Paramecium and other species needing a low oxygen content, a culture can be maintained for one or two years simply by adding small amounts of hay-stalks, lettuce or grain to the old culture as necessary, or by pouring off three-quarters of the old medium and replacing with fresh. Hay infusion was found a most useful general medium in this study, and lettuce, wheat-grain and flour-hay infusions were satisfactory.
Culture Media, etc.: (Quantities specified below for culture media — after Kirby 1950).
Hay Infusion: Boil 2 grm. of hay in water and add water (distilled or rain-water) to make 1.000 cc. The infusion may be made up in a more concentrated form (10 grm. hay to 1,000 cc), autoclaved and stored in sterile containers for future use. Dilute to the former concentration before use. Timothy hay is usually stated as the best medium. In the present study the dried flower stalks of cocksfoot (Dactylis glomerata) or similar grass was found very satisfactory.
Lettuce Infusion: Dry lettuce leaves in oven until crisp or brown (do not burn). Powder dried leaves. Boil 1.5 grm. lettuce powder in 1,000 cc. distilled water for 5 minutes. For use, add 1 part distilled water to 2 parts of stock lettuce infusion. (Note: Lettuce powder may be stored.)
Wheat Infusion: Boil wheat grains in a small amount of water for 2 or 3 minutes. Add the boiled wheat grains to the culture water. The number of grains used varies with the type of ciliate to be cultured, e.g. Paramecium 60-70 grains to a litre, Vorticella and Stentor 20 grains to a litre, and hypotrichs (in general) 40 to a litre.
Flour-hay Infusion: 0.1 grm. chopped hay and 0.13 grm. white flour. Boil for 10 minutes in 100 cc. water. Stand for 24 hours and dilute with an equal amount of water for use.
Media can be kept for some time in sterile tubes (place tube in boiling water for 15 minutes, then plug with cotton-wool and cool).
Specific Descriptions. (Classification follows that used by Kudo 1946.)
O. Holotricha. S.O. Gymnostomata. Tribe Prostomata. F. Colepidæ.
Coleps elongatus (Ehrenberg) *(Fig. 7.)
Body form constant, barrel-shaped; 13 to 15 rows of regularly arranged, smooth indurated ectoplasmic quadrangular platelets; narrow intervening furrows soft, possessing cilia; cytostome. anterior surrounded by slightly larger cilia than those of the body; three posterior spinous projections; single terminal contractile vacuole, clearly visible in life; macronucleus, rounded with micronucleus lying close to it. Length: 0.038 to 0.075 mm.
Commonly found in fish ponds, etc., and usually recognisable by its light brown colour and constantly rapid revolving motion with frequent changes of page 91 direction. Cultures easily in lettuce infusion. Good permanent slides can be made from Schaudinn-fixed, iron hæmatoxylin stained material.
Bary (1950) described C. hirtus Muller from a Wellington locality. This species differs from C. elongatus in being slightly smaller in size, 0.04 to 0.065 mm. as against 0.038 to 0.075 for C. elongatus, and in having a greater number of rows of ectoplasmic plates, viz. 15 to 20 rows. Both species possess 3 caudal spines.
References: Kudo, 1946; Bhatia, 1936.
S.O. Trichostomata. F. Parameciidæ.
Paramecium caudatum (Ehrenberg). (Fig. 2.)
P. caudatum is the most widely distributed species of Paramecium and occurs in freshwater ponds, streams, etc., particularly those with a high bacterial content. The species is described and figured adequately in all elementary zoological texts. Length 0.18 to 0.30 mm. Two species of paramecium that may be confused with P. caudatum are P. multimicronuleatum and P. aurelia. The former is similar in shape to P. caudatum but is distinguished by having 3 to 7 contractile vacuoles and at least 4 vesicular micronuclei. P. aurelia is also similar in shape but smaller than P. caudatum, but differs from the latter in having 2 small vesicular micronuclei and a more rounded posterior end. P. caudatum cultures, well in hay infusion, fixes well with warm Schaudinn's and stains readily with Heidenhain's or Erhlich's hasmatoxylin. Reference: Kudo, 1946.
Paramecium bursaria (Ehrenberg). (Fig. 1.)
Body, foot-shaped, somewhat compressed and ellipsoidal in cross-section; body ciliation uniform except at posterior end where cilia are slightly longer; peristome very broad; macronucleus large, micronucleus compact; 2 contractile vacuoles; symbiotic zoochlorellæ often present. Length, 0.10 to 0.15mm., width 0.05 to 0.06 mm. Freshwater ponds, etc. Cyclosis is well marked, but locomotion is slow (not as active as P. caudatum). This species may be confused with P. putrinum which is similar in size and shape but has one contractile vacuole, an elongate macronucleus and no zoochlorellæ. Fix and stain as for P. caudatum. Reference: Kudo, 1946.
Paramecium trichium Stokes *. (Fig. 4.)
Body, oblong and somewhat compressed; peristome, long and conspicuous; macronucleus, kidney-shaped; micronucleus single and compact; 2 contractile vacuoles. Length, 0.06 to 0.12 mm. Common in stagnant waters, cultures readily in lettuce and wheat infusions. Reference: Kudo, 1946.
S.O. Hymenostomata. F. Frontoniidæ.
Colpidium colpoda (Ehrenberg). (Fig. 3.)
Body form constant, oval; ciliary rows run obliquely from right to left across the body anterior to the cytostome and longitudinally behind this region; an obvious junction marks the meeting point of the oblique and longitudinal ciliary rows; 4 posterior elongate cilia; cytostome roughly triangular and terminating in a food vacuole; macronucleus oval; contractile vacuole posterior. Length. 0.09 to 0.15 mm.page 92
Fresh and salt water. Cultures easily in lettuce infusion. Found here in Waiwhetu Stream and Judgeford Stream. References: Kudo, 1946; Bary, 1950.
Cyclidium glaucoma (Ehrenberg). (Fig. 9.)
Body, elongate, ovoidal; cilia long, fine, rigid, arranged in longitudinal rows but anterior truncated extremity devoid of cilia; caudal seta long and posteriorly directed: peristome with large hood-like membrane along the edge; macronucleus spherical and central; contractile vacuole terminal in position. Length, 0.02 to 0.03 mm.
Cosmopolitan, in swamps and ponds and found here in the Karori Reservoir, Wellington. Locomotion jerky. Cultures well in lettuce infusion, not so successfully in hay infusion. References: Ward and Whipple, 1945; Kudo, 1931; Bary, 1950.
Ctedoctema acanthocrypta (Stokes)*. (Fig. 20.)
Body ovoid, slightly truncate anteriorly; caudal cirri present; pellicle refractile: peristome at right midline with a membrane on right peristomial ridge; macronucleus anterior ovoid and associated with small micronucleus; contractile vacuole posterior in position. Length, 0.02 to 0.03 mm.
Common amongst decaying vegetation in beech forest tarns, Butterfly Creek, Wellington. Size range of the present specimens smaller than those given by Kudo, but otherwise the characters are those of C. acanthocrypta. Reference: Kudo, 1946.
O. Spirotricha. S.O. Heterotricha. F. Metopidæ
Metopus es Muller *. (Fig. 14.)
Body form variable, when extended oblong to fusiform; body ciliation uniform and longitudinal, some specimens having larger cilia forming a spiral at the end; peristome conspicuous, slightly spiralled, beginning at the anterior end and extending to the middle of the body; when contracted, peristome distinctly spirally coiled; cytopharynx short; macronucleus ovoidal to elongate; conspicuous terminal contractile vacuole. Length, 0.12 to 0.20 mm. Obtained from tropical aquarium tank. Cultures well in lettuce infusion. Reference: Kudo, 1946.
Metopus spiralis Kahl*. (Fig. 19.)
Body form variable, narrow to widely oval (according to habitat) but always easily recognised; anterior end rounded or slightly pointed, posterior end broadly rounded and possessing many rather elongate cilia; body ciliation relatively uniform, in longitudinal rows except for a zone of 5 to 7 rows of cilia which lie anterior to, and parallel with, the peristomial groove, and spiral diagonally in the same manner as the groove; peristome a conspicuous groove, spirally coiled, commencing anteriorly and passing diagonally across the body to terminate posteriorly in an undulating membrane; macronucleus spherical, situated half-way along the body; contractile vacuole large and terminal; a prominent group of large granules are found in the anterior region of the body; colour variable — yellowish to brownish violet. Length, 0.075 to 0.50 mm. Swims with a flexible rotating motion. Obtained from a tropical fish tank. Reference: Kahl, 1932.
Spirostomum amibiguum Ehrenberg. (Fig. 16.)
Body elongated, cylindrical, length to breadth ratio 10: 1; caudal cilia thigmotactic and secrete mucous threads; ectoplasm with well-developed myonemes (which are arranged lengthwise independent of the ciliary rows), hence the body is highly contractile; peristome extending two-thirds down the body and closely lined with a short membranelle; macronucleus moniliform and twisted, beads rounded to oval or elongated and tapering at both ends, numerous micronuclei rarely visible and less in number than the beads of the macronucleus; excretory vacuole large and terminal, with canal; colour yellowish to brown. Length, 0.8 to 1.0 mm. Cosmopolitan species found in ponds with fair amount of vegetation, and found here in an aquarium tank; easily seen with the naked eye. Locomotion rapid, spiralling. Quick contraction makes for rather marked distortion of shape on fixing with Schaudinn's. References: Bhatia, 1936; Kudo, 1946; Bary, 1950.
Spirostomum intermedium Kahl*. (Fig. 17.)
Elongate, cylindrical, slightly depressed, broadening in the peristomial region; adoral zone of cilia slightly longer than the body cilia ectoplasm with highly contractile myonemes arranged lengthwise and independent of body cilia; peristome situated about half-way along the body, short, and lined with short membranelle; macronucleus moniliform extending almost the full length of the body; excretory vacuole large, terminal with a long dorsal canal extending almost to the anterior end; colour, yellowish-brown. Length, 0.28 to 0.31 mm., width (average) 0.020 to 0.030 mm.; length-breadth ratio 10:1.
Freshwater, found in an aging Paramecium culture of material obtained locally. The body length of the present specimens is shorter than the 0.40 to 0.60 mm. recorded by Kahl but all other characters for the species are in accordance with those given by Kahl. References: Kahl, 1932; Kudo, 1946.
O. Spirotricha. S.O. Heterotricha. F. Stentoridæ.
Stentor roeseli (Ehrenberg)*. (Fig. 22.)
Body elongate and with groups of long cilia here and there; highly contractile; anterior end, trumpet-shaped; posterior end drawn out and terminating in a flattened attachment disc; longitudinal and horizontal striations visible in the anterior trumpet-shaped region; anterior disc curves and sinks towards the cytostome and bears long cilia which create a feeding current; cytostome leading to ciliated cytopharynx clearly visible in feeding individual; macronucleus long, and band-like; contractile vacuole large and distinct, situated anteriorly on the left of the cytopharynx and with a collecting canal extending for two-thirds the body length; yellowish-white to greyish-white in colour with many food vacuoles. Length: 0.5 to 1.0 mm. Collected from freshwater aquarium. Reference: Kudo, 1946.
S.O. Oligotricha. F. Halteriidæ.
Halteria grandinella Muller. (Fig. 21.)
Body urn-shaped, setiform cirri arising in threes from obliquely placed equatorial indentations; peristome small with vibratile membrane on one side page 94 and cirri on the other; oral aperture terminal and associated with a wreath of large cirri; macronucleus round and central; contractile vacuole central in position. Length, 0.025 to 0.030 mm. Commonly occurring in streams and stagnant ponds around Wellington. Free swimming, moving by rotary motion accompanied by sudden leaps. May be cultured in hay and lettuce infusions. References: Bhatia, 1936; Ward and Whipple, 1945; Kudo, 1946; Bary, 1950.
Halteria grandinella var. chlorelligera (Kahl)*. (Fig. 15.)
Body spherical or broadly fusiform; 15 large cilia form a clockwise adoral zone; equatorial region of body bears long bristles but is not ciliated otherwise; macronucleus oval and micronucleus also present. Length, 0.04 to 0.05 mm.
Common in pond water and found here. Distinguished from the variety cirritera by the presence of zoochlorellæ and more slender body-cirri. Locomotion is by rotation about the oral-aboral axis of the body accompanied by sudden leaps. References: Kudo, 1946; Ward and Whipple, 1918.
S.O. Ctenostomata. F. Epalcidæ.
Epalxis mirabilis Roux*. (Fig. 18.)
Horseshoe-shaped, with the anterior end slightly pointed towards ventral surface; posterior end irregularly truncate; dorsal surface more convex; right side of body with one dorsal and one ventral ciliary row in the posterior region; usually three conical tooth-like structures without spines on the left side and four on the right side in the anal region; comb-like structures lie posterior to the oral aperture; two large oval macronuclei situated close together in a dorsal position; large posterior ventral contractile vacuole. Length, 0.038 to 0.045 mm.; width, 0.027 to 0.030 mm.
Lives in sludge and found in tropical fish tank. Locomotion by irregular, slow jerky movements. Good permanent slides can be made from Schaudinn-fixed, iron hæmatoxylin stained material. References: Kahl, 1932; Kudo, 1947.page break
Fig. 1: Paramecium bursaria, ventral view. Fig. 2: Paramecium caudatum, left lateral view. Fig. 3: Colpidium colpoda, right lateral view. Fig. 4: Paramecium trichium, dorsal view. Fig. 5: Vorticella microstoma, left lateral view; A, fully extended specimen; B, encysted specimen. Fig. 6: Vorticella nebulifera var. similis; A, extended specimen, left lateral view; B, view from above. Fig. 7: Coleps elongatus, dorsal view. Fig. 8: Pyxidium cothurnoides, lateral view. Fig. 9: Cyclidium glaucoma. Fig. 10: Vorticella microstoma, telotroch formation.
Abbreviations: C, contractile stalk; CA, caudal teeth; CS, cytostome; CV, contractile vacuole; CY, cytopharynx; FD, frontal disc; FV, food vacuole; MN, micronucleus; N, nucleus (usually macronucleus); OT, oral teeth; P, peristome; PD, peristomial disc; PL, plates; TR, trichocyst; UM, undulating membrane; V, vestibule; Z, zoochlorellæ.
S.O. Hypotricha. F. Oxytrichidæ.
Stylonychia putrina Stokes. (Fig. 11.)
Body form constant, ovoid to reniform, ventral surface flat, dorsal convex; eight frontal, five ventral, five anal and three caudal cirri, and with a continuous border of marginal cirri; peristome half as wide as the body; two macronuclei, oval or elongate; contractile vacuole single, spherical, situated near the posterior angle of the peristome. Length, 0.125 to 0.150 mm. Cosmopolitan species, common in ponds and found here in fish-ponds. Locomotion rapid, both by swimming and creeping. Cultures readily in lettuce infusion. References: Kudo, 1946; Bhatia, 1936; Bary, 1950.
Stylonychia mytilus Ehrenberg. (Fig. 12.)
Body ovoid, left side straight; ‘giant’ and ‘dwarf’ forms may occur along with normal individuals; 8 frontal cirri (typical of the genus) are usually present and 5 ventral cirri, but variable, sometimes with 7 ventrals; peristome with a protruding upper lip and an undulating membrane; 2 large macronuclei each with a closely associated compact micronucleus; contractile vacuole on left side posterior to peristome. Length, 0.10 to 0.30 mm.
Abundant among decaying vegetation in Waiwhetu stream. Feeds very actively on algæ and diatoms. Reference: Kahl, 1932.
Steinia platystoma*. (Fig. 13.)
Body form fairly constant, but proportions of length to breadth variable (2: 1 up to 2.5: 1); posterior end tail-like, anterior end flattened, left side straight, right side convex, making the body asymmetrical and bluntly rounded anteriorly; marginal cirri long, with three barely differentiated caudal cirri; peristome roof-like and has a ventral ectoplasmic fold or inner lip; large undulating membrane present between outer and inner ectoplasmic lip and ends in the same position as the outer lip; endoplasm yellow, thickly but evenly granulated. Length, 0.08 to 0.13 mm. Reference: Kahl, 1932.page break
Fig. 11: Stylonychia putrina, ventral view. Fig. 12: Stylonychia mytilus, ventral view. Fig. 13: Steinia platystoma, ventral view. Fig. 14: Metopuses, dorsal view. Fig. 15: Halteria grandinella var. chlorelligera, ventral view. Fig. 16: Spirostomum ambiguum, right lateral view. Fig. 17: Spirostomum intermedium, right lateral view. Fig. 18: Epalxis mirabilis, left lateral view. Fig. 19: Metopus spiralis, dorsal view. Fig. 20: Ctedoctema acanthocrypta. Fig. 21: Halteria grandinella. Fig. 22: Stentor roeseli, ventral view.
Abbreviations: AC, anal cirri; AD, adhesive disc; AZ, adoral zone; CC, caudal cirri; CT, collecting tubule; CV, contractile vacuole; CY, cytopharynx; FC, frontal cirri; FV, food vacuole; LS, left side; MC, marginal cirri; MO, moniliform nucleus; N, nucleus; OD, oral disc; OG, oral groove, P, peristome; PC, peristomial cirri; RS, right side; SC, setiform cirri; T, teeth (tooth-like processes); UM, undulating membrane; VC, ventral cirri; VM, vibrating membrane; Z, zoochlorellæ.
O. Peritricha. S.O. Sessilia. Tribe Aloricata. F. Epistylidæ.
Pyxidium cothurnoides Saville Kent*. (Fig. 8.)
Body vasiform, widest centrally; frontal ciliary disc small and oblique and has two circles of fine cilia; stalk simple (not branched) and very short; body surface smooth, no striations; peristome not constricted from the body proper; macronucleus elongate bean-shaped; single contractile vacuole. Length, 0.09 to 0.10 mm.
Attached to freshwater animals (Kudo) and found here in ‘silage’ heap vegetation. References: Kudo, 1946; Ward and Whipple, 1918.
Body form bell-like, slightly ovate with a narrow ciliated peristomial disc surrounded by a thin ring-like margin; pellicle annulated; contractile stalk present and contractile fibres often visible towards the base of the body; peristome short but with long œsophageal fibres; macronucleus large and band-like, micronucleus present; large, contractile vacuole; colour, yellowish. Length, 0.065 to 0.083 mm.; width, 0.022 to 0.050 mm.. Stalk size: Length, 0.020 to 0.385 mm.; width, 0.0015 to 0.0040 mm.
Solitary, attached to submerged objects. Obtained from a slow-moving stream at Butterfly Creek, Wellington. The species readily encysts. At the commencement of encystment the stalk contracts and coils spirally; at the same time the body encysts, the peristomial disc being contracted and the body folding up and over the peristomial region. Encystment is rapid under artificial conditions. The species has the ability to live in bacteria-rich cultures. Telotroch formation takes place under conditions of low oxygen tension. This was observed on more than one occasion in the present study. The sessile animal develops a posterior ring of strong cilia, breaks away from its stalk proximally and leads for a time a free swimming existence. The time occupied from the appearance of the cilia (Fig. 10B) until the animal becomes free varies from 5 to 10 minutes. During this time the cilia grow in length and their beat becomes progressively stronger until suddenly the body of the animal is freed from its stalk. Fig. 10 shows the formation of the telotroch.
References: Kudo, 1946; Bary, 1950.
Vorticella nebulifera var. similis Nolan and Finley. (Fig. 6.)
Body of an inverted bell-shape with slight but constant changes of form; pellicle smooth; stalk highly contractile; contractile fibres often visible towards the base of the body; peristomial disc broad and ciliated with a lip and vestibule leading into the cytostome; macronucleus horseshoe-shaped, micronucleus? (not seen in any of the material in the present study); contractile vacuole small and towards the distal end. Length, 0.053 to 0.067 mm.
Usually attached to submerged water plants (often Nitella). Gregarious. forming large masses easily visible to the naked eye. Reference: Bary, 1950.
Bary, Brian M., 1950. Studies on New Zealand freshwater ciliates: Part II. An annotated list of species from the neighbourhood of Wellington. Trans Roy. Soc. N.Z. 78 (2-3), pp. 311-323.
Bhatia, B. L., 1936. The Fauna of British India: Protozoa, Ciliophora. London.
Brand, 1946. ‘Anærobiosis in Invertebrates’. No. 4 of the Biodynamica monographs edited by B. J. Luyet Normandy, Mo., 328/b.
Kahl, A., 1932. Urtiere oder Protozoa: I. Wimpertiere oder Ciliata (Infusoria). Tierwelt Dtsch. Vol. 25, pp. 399-650.
Kent, W. S., 1880-82. A Manual of the Infusoria, Vols. I and II. London.
Kirby, Harold, 1950. Material and Methods in the Study of Protozoa. Univ. of Calif. Press.
Kirk, T. W., 1885. On some specimens of Vorticellæ collected in the neighbourhood of Wellington. Trans. N.Z. Inst. Vol. 18, pp. 215-217.
Kudo, R. R., 1946. Protozoology. Springfield, Illinois.
Maskell, W. M., 1886. On the Fresh Water Infusoria of the Wellington District. Trans. N.Z. Inst. Vol. 19, pp. 49-61.
——, 1887. On the Fresh Water Infusoria of the Wellington District. Trans. N.Z. Inst. Vol. 20, pp. 3-19.
Noland, L. E., and Finley, H.E., 1931. Studies on the Taxonomy of the Genus Vorticella. Trans. Amer. Micr. Soc. Vol. 44, pp. 3-13.
Stokes, A. C., 1888. Freshwater Infusoria. J. Trenton Nat. Hist. Soc. Vol. I (3), pp. 71-344.
Ward, H. B., and Whipple, G. C., 1918 and 1945. Fresh Water Biology. Wiley, N.Y.