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Four New Species of Fresh-water Ciliates from New Zealand

Order Holotricha — Family Frontoniidae — Genus Glaucoma Ehrenberg, 1830 — Glaucoma kirki sp. nov. Plate 1, Figs 1 to 6

page 3

Order Holotricha
Family Frontoniidae
Genus Glaucoma Ehrenberg, 1830
Glaucoma kirki sp. nov. Plate 1, Figs 1 to 6

The body shape, in mature individuals, is ovate to elongate ovate (Fig. 1), but almost globular shortly after fission. The anterior extremity is obtusely pointed and surmounted by a small, dome-like knob (Fig. 6), while the posterior extremity is broadly rounded, or, in a few specimens, bluntly pointed. The widest portion is posterior to the middle of the body, although starved specimens are more elliptical in shape. The dorsal surface is evenly convex, the ventral less so, while about the cytostome is a shallow concavity, producing the effect of a slight ventral curvature of the pre-oral region. The length lies between 25 and 45 mu, averaging 33 to 34 mu; the width, at the widest, lies between 17.5 and 24 mu. Occasional specimens are considerably longer or shorter, but such are abnormal in size; the shape is also unusual in these specimens, and is either globular or even broadened anteriorly. Such abnormalities are more frequent in old or unhealthy cultures. The proportion of breadth to length is 1:1.6 to 1.8; in starved specimens it may be higher, 1:2 or more.

The number of ciliary rows closely approximates 30; in the anterior two-thirds of the body they are well defined and the cilia more or less regularly spaced (Figs. 1 and 6), but posteriorly the spacing is irregular and the rows less well defined. A wide pre-oral suture (Fig. 6), running from the anterior left of the cytostome to the extremity of the body, is delineated by the anterior ends of five or six rows which almost meet after curving round from each side of the cytostome. The remaining rows (Fig. 6) converge towards the anterior extremity, ending at the base of the terminal knob. This and the suture are devoid of cilia. There is no indication of a post-oral suture. Five post-oral ciliary rows are usual (Fig. 6), but six have been counted. The cilia are 7 to 8 mu long and rather stout; towards the anterior extremity they are somewhat finer and the insertions are closer together. They occur in shallow depressions which often become confluent anteroposteriorly, the ciliary rows then being situated in longitudinal grooves in the pellicle. Though firm, the pellicle permits limited distortions to the shape of an organism forcing its way among debris.

The ingestive apparatus is anteroventrally placed (Figs. 1, 5, and 6). The anterior edge of the cytostome is one-fifth to one-sixth of the body length from the extremity, and the opening extends posteriorly to about one-third of the length. Its longitudinal axis lies at an angle of 15° to 20° to that of the body, sloping from the anterior right towards the posterior left. It is almost oval, but is flattened slightly on the left side. A funnel-shaped cytopharynx extends from the cytostome page 4 posterodorsally and to the left, and at the same time regularly decreases in diameter. Its innermost portion turns abruptly farther to the left, and from the angle, certain structures, which are possibly oesophageal fibrils, extend into the endoplasm. The structures are between 2.5 and 3.5 mu long, surround developing food vacuoles, much as described for the fibrils in Paramecium by Lund (1941), and in nigrosin preparations, appear to consist of several threads. Another possibility is that these are portions of a tubular extension of the cytopharynx. The fibrillar appearance and very considerable ability to distend to accommodate food vacuoles are arguments against this view. A rapid whirling of ingested bacteria in developing vacuoles could be credited to the actions of fibrils.

Four membranelles (Figs. 5 and 6) are present in the ingestive apparatus. Furgason (1940) designates them by numbers: membranelle 1 is on the left; membranelle 2, the next inner, and membanelle 3 is on the right of the cytopharynx and internal to the undulating membrane which lies along the right cytostomal margin. The uniseriate undulating membrane is wide, reaching halfway across the cytostomal opening. It begins near the anterior extremity of the cytostome, passes along the right and below the posterior margins on to the right wall of the cytopharynx along which it proceeds almost to the apex. Its cilia are stouter than those in the other membranelles. The biseriate membranelle 1 (Figs. 2 to 6) runs for a short distance transversely on the anterior face of the cytopharynx, curves abruptly through approximately 90°, and. proceeds posteriorly, at first laterally, and then towards its inner end, ventrolaterally, along the left wall of the cytopharynx. It is a wide membranelle, reaching across almost two-thirds the width of the cytostome. Membranelle 2 (Figs. 2 to 6) consists of from four to six rows of cilia. It begins short of the anterior face of the cytopharynx and curves and broadens as it passes along the dorsal face towards the left posterior extremity. Membranelle 3 (Figs. 2 to 6) runs close to, and almost parallel with, the undulating membrane; it is biseriate and nearly as long as membranelle 2. Furgason states that membranelle 3 is frequently overlooked, since in the live animal it is covered by the undulating membrane and membranelles 1 and 2. Such was the case also with live organisms in the present study, and it was not until nigrosin preparations and sections of the cytostome were correlated that the presence and extent of membranelle 3 were determined.

The ectoplasmic lip, or flange, is wide and pronounced. It arises on the right, anterior portion of the cytostomal margin and extends down to the posterior margin, which is slightly raised above the general body contour. The body surface is elevated and meets the outer edge of the flange, thus forming a small protrusion, readily seen from the right side. The post-oral ciliary rows are displaced a little to the right, where they extend on to the protrusion.

The singularly large macronucleus is rarely less in diameter than two-thirds page 5 the widest part of the body, and is usually centrally placed, but it may lie more anteriorly in the body. It is spherical, but the cytopharynx often causes flattening on the right side (Fig. 3). A decidedly coarse appearance is given it by large, more or less evenly-sized, deeply-staining granules of chromatin. A small vesicular micro-nucleus is present, usually adjacent to the macronucleus. Degeneration of the macro-nucleus may occur in individuals in old cultures. A slight or marked irregularity of shape—the outline being more or less strongly lobed—is followed by extrusion of spherical to subspherical masses of chromatin with a diameter up to one-third that of the original nucleus. No more than three of the masses were present at one time; more usually one or two. An occasional nucleus was seen with a spherical concavity, although no chromatin mass was detectable. Rapid disintegration of the masses probably accounts for this, and also for the fact that few of the masses occur at any one time.

The single contractile vacuole (Fig. 1) is on the right side towards the dorsal surface at the posterior one-quarter of the body length. It discharges by a single pore, visible in nigrosin preparations, but it was not possible to determine the meridian number in which it occurs. The cytopyge is almost posteroterminal on the ventral surface, and again the meridian was not determined. A longitudinal dimple remains for a short time following discharge of faeces.

Specimens were collected from Wainui-o-mata Reservoir and three localities at Upper Hurt, Wellington. In one collection, from a stagnant pond at Upper Hutt, specimens were extremely numerous, but in other collections, from moving water, they were few. This was no doubt because the species is a bacteria-feeder, and bacteria can be expected in higher concentration in the stagnant water. In well-matured hay infusions, subcultures develop very quickly, and the majority of specimens are commonly seen undergoing transverse fission; in older cultures fission is rare. Whenever large numbers of specimens are present, they periodically concentrate, forming whitish areas in the culture; such clusters occur in shallow or deep vessels, near the surface or deeper within the culture. A small population may persist for many weeks after the peak of reproduction has passed.

This ciliate is very restless, its movements rapid and frequently irregular. Forward motion is accompanied by open spiralling and rotation of the body about the longitudinal axis, both in a left-hand direction. Individuals often swim round a particle of debris and by keeping the ectoplasmic flange and undulating membrane in contact with its surface, scoop bacteria into the cytopharynx. Similar feeding habits have been reported for three other species of Glaucoma by Gelei (1936). A high degree of selection is shown for bacteria as food material, and neither other organic material nor finely powdered carmine were ingested.

Conjugation was observed on only two occasions, and in each instance one of the pair of conjugants was markedly larger than the other. The individuals were page 6 united by their ventral surfaces for the anterior two-thirds of their length, the cytostome being almost obliterated. Unfortunately, nuclear behaviour was not satisfactorily demonstrated in the preparations made.

Species of Glaucoma may be placed in two groups on the basis of body shape and proportions—those more or less elongate, with higher ratios of breadth to length, and those more shortly ovate. The first group comprises Gl. ficaria Kahl, Gl. sagitta Kahl, and Gl. bacillivorax Gelei. In the second group occur Gl. avellana Kahl, Gl. scintillans Ehrenberg, Gl. myriophylli Gelei, and the present material. Gl. pyriformis Maupas, a species more or less intermediate between the groups, was redescribed as Gl. maupasi by Kahl in 1926, but Furgason (1940) considers Gl. pyriformis is identical with his Tetrahymena geleii. Gl. ficaria is elongate, more or less pyriform, and has a short post-oral suture and marked ventral pre-oral curvature. Gl. sagitta has a breadth-to-length ratio of 1:4 or 5 and a very small cytostome. Gl. bacillivorax is more acuminate posteriorly than anteriorly, has a long post-oral suture and 55 to 61 ciliary rows. These features clearly differentiate the three species from the present material. Of the second group, Gl. myriophylli has up to 110 ciliary meridians and thus is excluded. Gl. scintillans and Gl. avellana more nearly approach the local materia] in general morphology. Gl. scintillans, however, is broadly and subequally rounded anteriorly and posteriorly, and is without the anteroterminal knob of local specimens, possesses a triseriate membranelle 3 and a macronucleus, the diameter of which is no more than one-third the width of the body. Kahl describes Gl. avellana as acuminate anteriorly, and there is no anteroterminal knob. The diameter of the macronucleus is no more than one-third that of the body. The membranelle pattern of the ingestive apparatus is similar, but membranelle 1 extends no farther into the cytopharynx than the posterior border of the cytostome and membranelle 3 is triseriate; the membranelles generally are narrower than in local specimens. He does not give the number of ciliary meridians, though 17 are shown in his figure of the ventral surface.

The most outstanding difference between the present material and the species in the second group is the large macronucleus. In no other species does it reach a comparable relative size. This, the biseriate membranelle 3, the ovate shape—bluntly pointed anteriorly and having the terminal knob, serve to differentiate the local species.

Wellington material is named Glaucoma kirki in memory of the late Professor H. B. Kirk, formerly Professor of Biology at Victoria University College.