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Four New Species of Fresh-water Ciliates from New Zealand

Family Stentoridae — Genus Stentor Oken, 1815

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.

page 10

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.