Pseudourostyla pelotensis, Paiva & Silva-Neto, 2006

Paiva, Thiago Da Silva & Silva-Neto, Inácio Domingos Da, 2006, Pseudourostyla pelotensis sp. nov. (Ciliophora, Stichotrichia, Urostylida): a new psammophilic ciliate from the southern Brazil, Zootaxa 1247 (1), pp. 43-58 : 45-52

Description of Pseudourostyla pelotensis sp. nov.

Diagnosis

Psammophilic Pseudourostyla Borror, 1972 , measuring about 190 x 80 µm in vivo (n = 15); body very flexible, with elliptical outline, dorsoventrally compressed in almost 2:1 proportion, with ovoid and ellipsoid colorless cortical granules and displaying a short beak­like projection oriented to the left at the anterior region of the cell. Two contractile vacuoles present. Somatic ciliature with a typical bicorona and urostylid midventral complex formed by a row of cirral pairs that ends just below the equatorial region of the cell. Pre­transverse cirri lacking; on average two frontoterminal cirri, one buccal cirrus, five left and six right marginal cirral rows; six transverse cirri and eight dorsal kineties. Adoral zone composed of about 50 membranelles.

Type locality

Laranjal beach, Pelotas, Rio Grande do Sul, Brasil. Geographic coordinates: 31º 45’ 34.05” S; 52º 15’ 38.43” W.

Species name

Named after its type locality: the city of Pelotas , located in the state of Rio Grande do Sul, Brazil .

Description

Pseudourostyla pelotensis sp.nov. presents thigmotactic behavior, usually hides in between sand grains and debris, crawling slowly on the bottom of the petri dishes and ascending to the water column only when disturbed. Cytoplasm is transparent, without pigments. Cells possess inconspicuous colorless cortical granules, which in protargolimpregnated specimens were identified as extrusomes that are of ovoid and ellipsoid shapes. These are distributed mainly as agglomerations around the bases of the cirri that compose the marginal and midventral rows, along the basis of the oral lip and some also occurring scattered. Measurements of the granules could not be properly taken from live specimens, but in protargol­impregnated cells they are about 2.5 x 1 µm. Cells also display small (ca. 2 – 4 µm) refringent cytoplasmic inclusions concentrated close to their posterior end ( Fig. 1a, c ; 3k; 4k). Live specimens were found to have two round shaped contractile vacuoles that pulsate at intervals of about 10 – 15 seconds, conspicuous at low magnification. The anterior vacuole is located near the dorsal side of the oral cavity and has two thin longitudinal collecting canals that become visible during contraction. The posterior vacuole is placed about at the equatorial level of the body, close to its left margin. During pulsation, this vacuole becomes ellipsoid and stretches longitudinally, revealing two collecting canals, being the anterior one noticeably longer. As usual, both vacuoles excretory pores open at the dorsal surface. No interconnection between the collecting canals of the vacuoles could be clearly seen ( Fig. 1a, b ; 3a, c; 4a – j).

The food vacuoles in the studied specimens usually contained flagellates, scuticociliatids, and other preys ( Fig. 3d). An increased number of ingested preys sometimes make the cells slightly opaque. A cytopyge was detected in the right­posterior region of the body ( Fig. 3b–c). Cells of P. pelotensis sp. nov. exhibit a short beak­like angular projection on the anterior­left edge of the body, noticeable from life and unrecognizable after impregnation with protargol, probably as effect of the fixation process ( Fig. 1a ; 3e, f, j).

The oral apparatus displays a conspicuous adoral zone of membranelles (AZM) that occupies about 36% of the body length, plus a pair of undulating membranes that virtually intercept each other at the proximities of their central portion, being consistent with the Oxytricha­ pattern (see Berger & Foissner, 1997; Berger, 1999) ( Fig. 1d ; 2f ; 5a; d ). In the smallest specimens present in our sample, this interception happens close to the proximal region of the undulating membranes ( Fig. 2a , 5a ) The AZM holds about 55 membranelles, and the ones located at the anterior end of the cell are about 15 µm long. Internal membranellar cilia are relatively long, being shown in Fig. 3h. The paroral membrane is settled on a prominent peristomial lip that partially covers the most proximal adoral membranelles with its proximal border, resembling the “angular” type (see Foissner & Al­ Rasheid, 2006), but with a conspicuous left wall ( Fig. 3f, h). Moreover the distal region of the paroral membrane is placed on average at 15 µm away from the anterior end of the cell and immediately left to the distal end of the endoral membrane. In addition, the oral cavity has an uncommon convex folding at its anterior border ( Fig. 3j). The pharynx ( Fig. 3d) extends to the equatorial region of the cell, curving to the inner right side of the body and being close to a subsurface bow­shaped argentophylic structure that is present in all studied individuals, and that is from where the new adoral membranelles are generated in early reorganizers ( Fig. 1d–e ; 2a–b ; 5a, d–e ). Judging from its focal plane in protargolimpregnated specimens, this structure can be assumed to be associated to the inner side of the undulating membranes ( Fig. 2b ; 5d ).

The frontal cirral conjunct consists of a typical bicorona where the posterior corona always begins slight to the left of the anterior corona and usually exceeds its number of cirri by one. The anteriormost and the posteriormost frontal cirri measure about 15–17 µm and 10 µm long respectively. Single thick buccal cirrus measuring approximately 15–17 µm long is located right of the central region of the paroral membrane. Two frontoterminal cirri located right to the bicorona, with exception of one specimen in our sample (n = 18) that displayed three. The urostylid midventral complex starts from directly behind the right end of the bicorona, and is formed by a sigmoid curved midventral row of about 13 cirral pairs that ends just below the equatorial region of the cell.

In the studied specimens we observed 4–6 left and 5–8 right marginal cirral rows which are settled on slight ventral furrows, easily seen in free­swimming cells ( Fig. 1a, d ; 2a, c ; 3e–h; 5a, d ). Due to the heavy impregnation of the organisms and numerous extrusomes, it was not possible to determinate the exact number of marginal cirri in all specimens from our slides, thus this character is undersampled. The left marginal rows are curved to the opposite margin of the cell at their posterior region. The outer two left marginal rows end in the dorsal surface, being the outermost one entirely disposed dorsally and commenced by a short row of dikinetids. One specimen within the studied sample presents a reduced second left marginal row, containing only 14 cirri. The right marginal cirral rows are formed by dikinetids at their anterior end, which are then followed by cirri. In addition, the number of preceding dikinetids grows from the leftmost to the rightmost right marginal row ( Fig. 2c ; 5a–b, f ). These rows are disposed oblique to the main body axis and commence on the dorsal surface, twisting to the ventral side and ending at the posterior end of the organism. Behind the terminal portion of the leftmost right marginal row and on average at 67 µm distant from terminal cirrus of the midventral complex, there are 5–9 transverse cirri that protrude beyond the posterior­left margin of the cell and measure about 20 µm ( Fig. 1a, d ; 2a ; 3i; 5a ). Pre­transverse cirri are absent.

In the dorsal surface there are approximately 7–11 rows of dikinetids, which except for the ones anteriad of the marginal rows, are difficult to follow due to their organization, and cannot be unambiguously counted ( Fig. 2c ; 5b ). Caudal cirri are absent.

The nuclear apparatus is composed of 62–114 spheroid and elliptical macronuclear nodules scattered along the whole cell interior and possessing conspicuous chromatin granules unveiled by protargol impregnation ( Fig. 2b ; 5d ). After such preparations, the spheroid nodules measure 3–4 µm in cross section, while the ellipsoid ones measure 4–5 µm long x 3–4 µm wide. In living specimens, the nodules were found to be slight smaller ( Fig. 2b ; 3d; 5d ). Micronuclei could not be recognized, very probably because they did not stain well with protargol. A morphometric characterization of P. pelotensis sp. nov. is presented in Table 1.

CV=coefficient of variation; M=median; Max=maximum value observed; Min=minimum value observed; n=sample size; SD=standard deviation; SE=standard error; =arithmetic mean. *L1 and R1 correspond to the innermost rows of the left and right marginal sets, respectively.

Figures

FIGURE 1. Schematic drawings of Pseudourostyla pelotensis sp. nov. a. Living specimen in ventral view; b. Scheme of living specimen showing the contractile vacuoles and their aspect during pulsation; c. Extrusomes aligned close to the pelicle, as seen in specimens from protargol slides; d. Ventral region of protargol­impregnated specimen; e. Bow­shaped structure associated with the undulating membranes. Arrow marks new adoral membranelles in formation. aC — anterior corona; aCV — anterior contractile vacuole; AZM — adoral zone of membranelles; BC — buccal cirrus; BS — bow­like structure; eM — endoral membrane; FTC — frontotermial cirri; LMR — left marginal cirral rows; MVR — midventral cirral row; pC — posterior corona; pCV — posterior contractile vacuole; pM — paroral membrane; RMR — right marginal cirral rows; TC — transverse cirri. Scale bars: 10 µm.

FIGURE 2. Schematic drawings of protargol­impregnated specimens. a. Ventral region. Arrow shows a variation of the virtual intersection of the undulating membranes; b. Dorsal region showing macronuclear nodules. Chromatin granulations are depicted in the two macronuclear nodules pointed by arrows. Asterisk marks the bow­shaped structure, which is visible at the macronucleus focal plane; c. Dorsal region showing dorsal kineties (arrow) and marginal cirral rows. LMR — left marginal cirral rows; Ma — macronuclear nodule; RMR — right marginal cirral rows. Scale bars: 10 µm.

FIGURE 5. Protargol­impregnated specimens. a. Ventral side; b. Dorsal side; c. Extrusomes (arrows); d. Oral apparatus and macronuclear nodules. Arrow points to bow­shaped structure associated to the undulating membranes; e. Formation of the new adoral membranelles during reoganizational morphogenesis (arrow); f. Ventral side of specimen with a shortened left marginal row (arrows). aC—anterior corona; AZM—adoral zone of membranelles; BC—buccal cirrus; DK —dorsal kineties; eM—endoral membrane; FTC—frontoterminal cirri; LMR—left marginal cirral row; Ma — macronuclear nodules; MVR—midventral cirral row; pC—posterior corona; pM— paroral membrane; RMR— right marginal cirral rows; TC— transverse cirri. Scale bars: 10 µm.