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Four New Species of Fresh-water Ciliates from New Zealand

Order Spirotricha

page 7

Order Spirotricha

Family Stentoridae
Genus Stentor Oken, 1815

Stentor loricata sp. nov. Plate 2, Figs. 8, 9

This species is deep, clear green, a colour produced by minute, dark green, sub-spherical granules within or immediately beneath the pellicle, and concentrated in bands (Figs. 8, 9) between colourless myonemes on the disc, body, and in the cytopharynx. Similar granules are scattered sparingly in the endoplasm. Nadler (1929) describes induced shedding of the pellicle in Blepharisma undulans, by which means he showed that the characteristic pink-purple to deep purple-violet colour is confined to the pellicle. In crushed local specimens, the pigment granules appear to be included in the pellicle, or at least are closely adherent to it, indicating the possibility of a condition similar to that in B. undulans.

Individuals are trumpet-shaped (Fig. 9), the posterior portion long and slender and rising from a small attachment area, flattened over the substrate. Anteriorly the body gradually widens and then expands rather suddenly to the slightly thickened margin of the disc. The disc surface is broad and funnel-like, does not protrude above the margin, but curves and sinks towards the cytostome (Fig. 9). In the ventral margin is a wide V-shaped notch, from the right of which a wedge-shaped ridge expands on to and merges into the disc surface and forms the anterior (upper) border of the cytostome. The margin on the left of the notch forms the ventral cytostomal border (Fig. 8). Transverse, regular striations on the margin of the disc of fixed specimens are produced by rows of pigment granules.

Extended animals range between 625 and 1150 mu long, and the disc between 140 and 240 mu wide. The proportion, disc-width to body-length is usually about 1:4.5, but varies between 1:3.5 and 1:6, the lower proportions occurring in smaller individuals.

Long, fine cilia cover disc and body surfaces. The anterior body cilia frequently beat towards the disc. Small groups of longer, stiff, setiform cilia occur on the anterior one-quarter to one-third of the body. The adoral wreath of long, strongly vibratile membranelles (Fig. 9) arises on the inner side of the disc margin, and is narrowly incomplete towards the point of the ventral notch. Continuous with the disc surface, and preceding the cytostome, is a large U-shaped, vestibular portion, seen only in extended animals. The margin on the left of the notch narrows gradually, and passes, together with the adoral membranelles, in a right-hand spiral into the cytopharynx. This spiral zone is readily seen in live animals. In prepared specimens there is a broad zone which spirals in a right-hand direction to the apex page 8 of the cytopharynx. This zone contains pigment granules in rows which run almost parallel to the longitudinal axis of the cytopharynx. The basal granules of the cilia appear to be situated adjacent to the rows of granules, but the latter prevented a clear demonstration.

The myonemes of the body are colourless, very narrow and threadlike posteriorly, and, although broader anteriorly, seldom exceed 3 mu in width. They are more numerous ventrally, where the intermyoneme pigmented areas are approximately one-half the width of those occurring laterally and dorsally. The U-shaped myonemes of the disc (Fig. 8) are most conspicuous in contracted individuals. To the right of the cytostome they commence along the margin and then curve away to the left side, where they aggregate into two groups, one terminating on the anterior margin of the cytostome, the other, larger group continuing into the cytopharynx in a spiral running parallel to the ciliary zone. The intermyoneme pigment area clearly demonstrates the course of the myonemes in the cytopharynx, and more lightly pigmented narrow bands, running longitudinally in this region suggest that the myonemes themselves are present. On contraction, the myonemes broaden, the pellicle over them becomes depressed, and that between adjacent myonemes arches upwards and is transversely and narrowly crinkled; the disc margin is then strongly crenulated and the body distinctly ridged and grooved. The body is elongately-conical to subcylindrical in the contracted state.

Stentor loricata is so named from the more or less cylindrical lorica (Fig. 9) covering three-quarters or more of the organism. Individuals readily forsake the lorica, especially after transfer to a hanging drop preparation. The free-swimming form is narrowly conical with a convex ventral surface. The disc margin is slightly less in diameter than the subsequent portion of the body; the disc surface is convex, though not markedly so, set obliquely to the longitudinal axis, sloping from the anterodorsal to the posteroventral surface. The attachment region, a short, ciliated projection, persists on the bluntly rounded posterior extremity. After a period as a free-swimming form, specimens reattach themselves and lorica secretion begins; the cilia of the posterior two-thirds or so of the body assume a setiform appearance, extend stiffly at right-angles to the body surface, and the material of the lorica is deposited outside their tips. Before debris attaches to the lorica, its presence is indicated only by the bent ends of the cilia, which on occasion are seen to force trapped particles into the lorica material. Frequent contractions and extensions of the animal during lorica formation apparently ensure that the completed lorica will be large enough to allow full withdrawal of the body.

The vermiform macronucleus (Fig. 9) is compact, finely granular, often twisted or coiled, and clearly visible as a lighter region in the living animal. Bishop (1923) reported for Spirostomum ambiguum, a species normally possessing a moniliform macronucleus, that the immature macronucleus was vermiform. In the many page 9 specimens examined in the present material, there was no hint of the moniliform character, the macronucleus being constantly vermiform. The species of Stentor with moniliform macronuclei are not then to be thought of as mature forms of the present material. There are several micronuclei, which are small and vesicular. No more than seven were seen in an individual, but the pigment granules make accurate determination very difficult, so that the number may be greater.

A large contractile vacuole (Fig. 9) is situated ventrally, on the left of the cytopharynx, and a narrow collecting canal extends posteriorly for half the body length. During diastole the vacuole is subtriangular, becoming spherical towards the end of this phase. The cytopyge is anteriorly and dorsally placed, to the left of the median plane. Previous to defaecation the faeces are contained in a vacuole which is conspicuous but smaller .than the contractile vacuole.

Reproductive stages were not observed.

Specimens were collected from a small stream at Akatarawa, Wellington, where they occurred attached to leaves and twigs in the water.

Previously described green species of Stentor, S. polymorphus (Muller), S. viridis, and S. oligonucleus, both described by Sokoloff (1930), S. amethystinus Leidy and S. mulleri (Bory) all owe their colour to Zoochlorellae and are not therefore to be confused with the present material. Maskell and Barraud described the green S. striatus from Wellington in 1887, but did not mention the colouring agent. In this species, however, the disc is not expanded and has an irregularly waved margin, and the length is almost twice that of the present specimens. Maskell's species is therefore readily distinguished on these characters.

Setiform cilia occur throughout the length of S. mulleri and in the anterior one-third to one-half of S. roeseli Ehrenberg, and, further, S. roeseli has a vermiform macronucleus. S. mulleri, however, contains Zoochlorellae; S. roeseli, according to to Pritchard (1841) in his translation of Ehrenberg, and to Roux (1901), is yellowish-white to greyish-white; in addition, the proportion, disc-width to body-length, is 1:2.5, the body stouter, the lorica smaller. It is improbable, then, that the present specimens are coloured S. roeseli.

The Wellington material possesses such a combination of distinctive characters in the vermiform macronucleus, deep clear green colour produced by pigment granules, setiform cilia, body proportions and large lorica, that a new species is warranted.

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Stentor rubra sp. nov. Plate 2, Figs. 10, 11

Individuals are coloured a diffuse rose-pink and when fully extended range between 250 and 448 mu long, with the disc between 70 and 100 mu wide. Thus, for a species of Stentor, the specimens are small. The body is narrowly and almost evenly conical, the disc slightly wider than the subsequent portion of the body; occasionally there is a very slight distension in the anterior one-third or one-quarter of the body. The proportion, disc-width to body-length, is 1:4.5 or 1.5. The disc, in extended specimens, is subcircular, slightly convex, but not protruding, and is posterior to the anterior edge of the body, which extends as a thin, deep, rim-like margin. The ventral margin is flattened, with, at its mid-length, a small V-shaped notch (Fig. 10), the margin on the left of which is lower than on the right. To the left of the median longitudinal plane, the disc dips sharply along an arcuate line to form a deep, U-shaped vestibular portion leading to the cytostome and cytopharynx. The membranelles of the adoral wreath are relatively longer than in S. loricata and arise from the base of the rim on its inner side. To the right of the ventral notch the wreath is narrowly incomplete, while on the left, the membranelles continue in a right-hand spiral into the vestibule-like portion and then into the cytopharynx. The body and disc are clothed by short fine cilia, which arise in numerous, very narrow, longitudinal grooves in the pellicle. No groups of setiform cilia occur.

The cytopharynx, a short narrow tube, curves posterodorsally; its cilia run in a right-hand spiral to its innermost portion, which appears to be permanently open into the endoplasm. Food vacuoles forming at this point are usually large and ovoid. No studies of the relationship of disc myonemes and cytopharyngeal structures were carried out.

Band-like, comparatively wide, regularly spaced, colourless myonemes run the length of the body (Fig. 10), but are indistinct and difficult to see on the disc. They produce a high degree of contraction, the body becoming squat and ovoidal and the disc margin widely, deeply, and regularly crenulated. On the rest of the body the pellicle is but slightly ridged between the myonemes, with correspondingly shallow grooves overlying them. In free-swimming forms (Fig. 11) contraction is not so great; the body is pyriform, with the disc retracted to between one-third and one-half the body width and not protruding beyond the general body contours. Following a short period as a free-swimming form, individuals "rub" the attachment area against debris, or place and withdraw it several times, such behaviour preceding reattachment. Attachment, effected by the extremity expanding and flattening page 11 over the substrate, is followed by a lengthy period of semi-extension, the more expanded form being but slowly assumed.

The contractile vacuole is to the left of the cytopharynx (Figs. 10 and 11), and a collecting canal extends into the posterior half of the body. At the end of diastole the subtriangular form changes to spherical. Systole is slow; the vacuolar membrane flattens on the right, then moves slowly towards the left, thus expelling the contents. A comparatively immense vacuole which distends the anterior region of the body forms slowly prior to defaecation; in one specimen it measured 30 mu, in another, 24 mu, in diameter. It discharges through a temporarily large, ovoidal opening on the dorsal surface, posterior to the disc margin.

Specimens were collected from an open-air aquarium on the roof of the Biology Block, Victoria University College, where they occurred attached to flocculated masses of a unicellular alga. They were not numerous, and attempts at subculturing were only, partially successful.

To my knowledge there is one other pink Stentor described—S. igneus Ehrenberg. Pritchard (1841) translates Ehrenberg as saying that S. igneus is "the fire-coloured Stentor," and later adds, "the skin is bright yellow or vermilion." Kent (1880–1882) states that the body possesses "a rich layer of Chlorophyll-granules," but that "the more superficial, transparent layer . . . contains a finely granular pigment of an intense scarlet hue." He also gives as his opinion that an inadequately described and figured, bright rose-coloured species, S. roseus De Fromental, is apparently referable to S. igneus. De Fromental's work is not available to me; Kent, however, expresses considerable doubt as to the soundness of his observations and the completeness of his diagnosis, so that it appears justifiable to accept Kent's view that S. igneus was the species described. Kahl's (1932) paper is unobtainable, but Kudo reproduces his figure of S. igneus and says it is rose-coloured or colourless. Roux (1901) shows precisely the colour of the present material. Although colour is a variable characteristic among most of the coloured ciliates, to judge from these accounts, there is a very wide degree of variation indeed in S. igneus.

Ehrenberg and Kent report S. igneus as being one seventy-second of an inch long (353 mu approximately), Roux as 200 to 400 mu long, and these measurements fall close to or within data for local specimens. The ratio of disc-width to body-length differs, however, from author to author. Kent reports the peristome as "equal to about one-half the entire length," and he figures a short, widely flared page 12 specimen. Kahl's figure indicates a disc-width of about one-third the body-length and actually narrower than the immediately posterior region of the body, which is bulbous over the anterior one-third to one-half of the body, a feature not referred to by other writers. Roux describes S. igneus as generally less conical and elongated than other species of Stentor and as broadly rounded and little contracted posteriorly; the disc-width, as illustrated, is a little less than half the body-length. The present material is then slenderer and differently proportioned. Groups of setiform cilia and a wide non-ciliated region of the ventral notch are further differences which Roux describes. He states that S. igneus is usually free-swimming; his figure suggests this, and, if so, the evenly curved body margins and wider disc bear little resemblance to the pyriform, free-swimming Wellington specimens (Fig. 11).

All writers describe a spherical or subspherical macronucleus for S. igneus, and this and similar size ranges are the only common features covering the descriptions available. Other characteristics described vary so grossly that it seems probable that more than one form of Stentor has been included within the species. The present specimens, which are slender, narrowly conical, coloured rose-pink, seldom free-swimming, and which have a distinct, rim-like margin to the disc, thus differ from any one of the descriptions for S. igneus.

Family Oxtrichidae
Genus Uroleptus Ehrenberg, 1834
Uroleptus setiformis sp. nov. Plate 1, Fig. 7

Specimens (Fig. 7) are subfusiform, the anterior extremity rounded, the posterior portion drawn out into a caudal process of approximately one-fifth the body-length and curved to the right. A narrow crescentic lip projects from the flattened ventral surface and lies about the anterior extremity. The right margin is evenly and strongly convex from the anterior extremity to the base of the caudal process. The central portion of the left margin is also convex, but to a lesser degree than on the right; anteriorly it is concave, which produces the effect of a sinistral flexion of the anterior one-fifth to one-quarter of the body. The dorsal surface is strongly convex, and, except for the extremities, where pronounced flattening occurs, is almost as deep as wide. Specimens range in length from 165 to 204 mu, and in width from 45 to 60 mu.

There are two rows of ventral, a single row of marginal, and three frontal cirri, and, as well, one row of fine setiform cilia laterally and a median longitudinal row dorsally. The three frontals are set in line obliquely across the anterior extremity, the left-hand cirrus occurring at the anterior end of the right peristomal margin. Two rows of ventrals begin towards the right anterior extremity and extend page 13 posteriorly to the tip of the caudal process; the left row is headed by the right frontal cirrus, and contains the larger cirri, especially anteriorly. The right marginals are larger and more conspicuous than the left, not flattened, and project anteriorly and posteriorly, the intervening ones being up to one-quarter of the body-width in from the margin. The left marginals commence level with the apex of the peristome, and in this region are short and fine. Posteriorly they lengthen, become more nearly equivalent with those on the right, and project beyond the margin. The caudal process is markedly setose, the cirri of the ventral and marginal rows projecting at varying angles. The dorsal and marginal setiform cilia are short and fine, and extend at right-angles to the body surface. The marginal setae arise from a slightly dorsal position, are often irregularly spaced posteriorly, or may be absent from portions of the caudal process. The dorsal setae correspond in length with, but are more regularly spaced than, the marginal setae.

A V-shaped peristome occurs anteroventrally on the left, occupying one-quarter to one-third the body-length, and having its right margin curved to the left anteriorly. Along the left margin is an adoral zone of membranelles which is continuous with the frontal zone. The latter consists of long, strongly beating cirri, arising from about the anterior body margin dorsal to the ventral lip. A wide, conspicuous, undulating membrane, its cilia readily seen in live organisms, lies on the right peristomal margin. Following the cytostome, at the apex of the peristome, is a short cytopharynx which curves to the left. The undulating membrane continues on to the right cytopharyngeal wall, but the adoral membranelles do not go beyond the cytostome.

A single contractile vacuole is on the left, between the peristomal apex and body margin within the anterior one-third of the body. It causes a conspicuous bulge in the margin during diastole. A short collecting canal extends anteriorly, and a longer one posteriorly to beyond the middle of the body.

Several features, similar to those found in other species of Uroleptus, include the two oval macronuclei, each with a comparatively large, closely associated, compact micronucleus; the cytopyge opening dorsally on the left near the base of the caudal process; the coarsely granular, greyish-brown endoplasm often containing fat globules and ingested diatoms.

Specimens were collected from two localities near Wellington, a semi-permanent pond at Maori Bank, Upper Hurt, and a tarn on Bull Mound (4,000 feet) in the Tararua Range.

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Among other species of Uroleptus, U. piscis Ehrenberg, is 600 to 800 mu long and has a very long caudal process; U. mobilis Engelmann, 300 to 400 mu long, is very narrow, has an excessively short peristome, and a moniliform macronucleus; U. musculus Muller, though approximately the same size, is proportionately wider than local specimens, is short and stumpy, and has a conical caudal process. U. longicaudatus Stokes is approximately eight times as long as wide, and U. sphagni Stokes is clavate to broadly obovate and about three times as long as wide. U. rattulus Stein has a very long caudal process, and U. violaceaus Stein, apart from being a very brilliant violet colour, possesses a truncated posterior extremity. A recently described species, U. halseyi Calkins (1929), is long and slender, with a moniliform macronucleus. Consideration of such features will avoid confusing these previously described species with the present specimens of Uroleptus. Two further species, U. limnetis Stokes and U. dispar Stokes, resemble local material, but differ in details. The distribution of the frontal cirri in U. limnetis and local specimens is similar, but U. limnetis possesses long, numerous dorsal setae and is thus effectively differentiated. In U. dispar the two right frontal cirri are side by side, almost parallel to the anterior body margin, but the third, left cirrus is more posterior, close to the right side of the peristome field, and not at the extremity of the right margin as in the present material. A distinctive feature is the presence of anterior and posterior collecting canals in local material. These, to my knowledge, have not been previously described in any species of Uroleptus.

While there is no doubt that only an undulating membrane is present on the right peristomal border in the present material, earlier descriptions of organelles in the peristome are variable. Both Calkins (1929) and Engelmann (quoted by Calkins) describe only undulating membranes; Stokes (1888), however, describes that, for U. dispar, the right peristomal margin is ciliated and "apparently has an undulating membrane"; for U. limnetis, that the undulating membrane is absent, but cilia are present; and for U. longicaudatus, that only an undulating membrane is present. In the related genus Stylonychia, the organelles on the right of the peristome were also variously described until Lund (1941) showed that an undulating membrane, together with endoral fibrils, were the only structures present. It is not necessary that the structures along the right peristomal margin should be identical in both genera, but it is strange that, for a conservative organelle such as the peristome, there is so much variation in Uroleptus, and it seems probable that further investigation will show that only an undulating membrane is present.

The combination of well-defined characters—the distribution of the frontal cirri and the form and distribution of the marginal and dorsal setiform cilia, the form and structures of the peristome, the shape and proportions of the body, and the presence of collecting canals—are such as to warrant a new species for the present material.