Apostylonychia baugilensis, Omar & Jung, 2024

Apostylonychia baugilensis sp. nov.

( Figs 1–4 View Figure 1 View Figure 2 View Figure 3 View Figure 4 ; Table 1 View Table 1 )

ZooBank registration: urn:lsid:zoobank.org:act:4AC87F88-DD5E-4592-A9A3-FEDFD36F16D9 .

Diagnosis: Body size 130–210 μm × 55–90 μm in vivo and 108–144 μm × 47–62 μm after protargol impregnation. Body length:width ratio 1.9–2.5:1. Two separate macronuclear nodules. Right marginal row composed of 18–21 cirri, left row of 13–16 cirri. Dorsal kinety 4 as long as kinety 3. Adoral zone occupies 48%–57% of body length and is composed of 42–46 membranelles.

Type material: The slide containing the holotype ( Figs 1B, C View Figure 1 , 3A, B View Figure 3 ; NNIBRPR27176 ) GoogleMaps and one paratype slide ( NNIBRPR27177 ) with protargol-impregnated specimens have been deposited in the Nakdonggang National Institute of Biological Resources , Korea. Two paratype slides ( GUC006653 and GUC006654 ) have been deposited in the Jung laboratory (J.-H. Jung) in Gangneung-Wonju National University.

Type locality: Temporary puddle (after rainfall) on a footpath (Baugil) behind the Gangneung-Wonju National University   GoogleMaps , Gangneung, South Korea (37°45′54.47″N, 128°52′34.28″E).

Etymology: The species-group name refers to the name of the footpath where it was discovered, i.e. the Baugil path in Gangneung, Gangwon province.

Morphological description: Size 130–210 μm × 55–90 μm in vivo (usually ~180 μm × 80 μm, N = 7) and 108–144 μm × 47–62 μm after protargol impregnation. Body obovate, widest in mid of adoral zone of membranelles, anterior end broadly rounded, frontal area in Laurentiella strenua (Dingfelder, 1962) Berger & Foissner, 1989 and Stylonychia mytilus (Müller, 1773) Ehrenberg, 1830 type, i.e. flat, almost circular, and wide, shifting frontal cirri to the right of the ventral side; scutum hyaline, broadly rounded and truncated to left; body margins gradually converging posteriorly, usually both margins straight, sometimes slightly convex or concave. Length:width ratio 1.9–2.5:1, on average 2.2:1. Dorsoventrally flattened, with middle half of dorsal side distinctly convex, posterior portion strongly flattened ( Figs 1A–C View Figure 1 , 2A–C View Figure 2 , 3A–F, I View Figure 3 ). Nuclear apparatus commences at ~23% of body length and ends at ~72%. Invariably two macronuclear nodules and two micronuclei. Individual macronuclear nodules ellipsoidal, in or left of the midline of the body, in vivo ~30 μm × 15 μm. Micronuclei usually attached to macronuclear nodules, spherical, ~5 μm across ( Figs 1C View Figure 1 , 3B View Figure 3 ). Contractile vacuole anterior to mid-body at left cell margin; ~17 μm across at end of diastole. Collecting canals present but hardly recognizable ( Figs 1A View Figure 1 , 2B, C, H View Figure 2 ). Cortex rigid and colourless; cortical granules lacking. Cytoplasm hyaline, studded with lipid droplets, refractive crystals throughout cell, and food vacuoles ≤20 μm across containing bacteria, yeast, flagellates, and starch grains ( Figs 1A View Figure 1 , 2A–H View Figure 2 ). Cells usually stand still or crawl slowly on the bottom of the culture dish, rarely swimming by spiralling around long body axis.

Cirral pattern of Apostylonychia baugilensis usually in Stylonychia mytilus pattern, i.e. 18 FVT cirri arranged as follows: three enlarged frontal cirri distinctly shifted to the right, with cilia 30–33 μm long in vivo; one buccal cirrus with cilia ~30 μm long in vivo; four frontoventral cirri arranged in V-shaped pattern, with cilia ~25 μm long in vivo; three postoral cirri in inverted L-shape pattern, with cilia as long as those of frontoventral cirri, cirrus IV/2 usually at the same level as cirrus V/4; two obliquely arranged pretransverse cirri, with cilia as long as those of postoral cirri; and five transverse cirri arranged in two groups, three left and two right, subterminal, only the two right cirri project from posterior body end, fringed distally, ~35 μm long in vivo ( Figs 1A, B View Figure 1 , 2A, E View Figure 2 , 3A, C, G, I View Figure 3 ). Marginal cirri fine, gradually decreasing slightly in size posteriorly, i.e. anterior cirrus of right marginal row ~25 μm long and posterior cirrus ~20 μm long. Right marginal row commences subapically at ~18% of body length and ends at ~95% of body length, composed of 18–21 cirri. Left marginal row commences at ~48% of body length and ends at posterior body end, composed of 13–16 cirri. Gap between posterior end of marginal rows slightly shifted to right ( Figs 1A, B View Figure 1 , 3A, C, F–H View Figure 3 ).

Six dorsal kineties, including two dorsomarginal ones, with bristles ~4 μm long in vivo. Kineties 1–4 bipolar, not curved anteriorly, possessing 35–43, 29–35, 26–33, and 23–31 dikinetids, respectively. Dorsomarginal kineties 1 and 2 extend posteriorly over ~55% and 43% of cell length and possess 12–19 and 6–12 dikinetids, respectively. Three caudal cirri, ~35 μm long in vivo, slightly shifted to the right, one each at end of kineties 1, 2, and 4; cirri usually beating fast ( Figs 1C View Figure 1 , 2B, C, F–H View Figure 2 , 3B, D–F, H View Figure 3 ).

Adoral zone occupies 48%–57% of body length and is composed of 42–46 membranelles. Distal end of adoral zone at ~15% of body length (DE-value 0.24 on average ( Berger 2006: 18)). Cilia of membranelles ~28 μm long in vivo, bases of largest membranelles ~7 μm wide after protargol impregnation. Buccal cavity wide, i.e. transverse distance between anterior end of paroral membrane to opposite adoral membranelle on left side, 24–33 μm wide and narrowing posteriorly ( Figs 1A, B View Figure 1 , 2A, D View Figure 2 , 3A, C, E, I View Figure 3 ). Undulating membranes in Stylonychia pattern, i.e. parallel or slightly overlapping. Paroral membrane commences anterior to buccal cirrus at ~25% of body length, with a length of ~30 μm in protargol-impregnated specimens, and extends to near buccal vertex. Endoral membrane commences posterior to anterior end of paroral at ~27% of body length, with a length of ~29 μm after protargol impregnation, and extends to buccal vertex. Membranes at the midline of the body, cilia ~13 μm long. Pharyngeal fibres extend transversely to the right body margin ( Figs 1A, B View Figure 1 , 2D View Figure 2 , 3A, C, I View Figure 3 ).

Morphogenesis: Apostylonychia baugilensis divides in the same ontogenetic pattern as Tetmemena bifaria described by Wirnsberger et al. (1985) and is characterized as follows: in the very early dividers, the oral primordium originates apokinetally as a longitudinal line of basal bodies left and anterior to the leftmost transverse cirrus, then the line spreads anteriorly and becomes wider in outline ( Figs 3I View Figure 3 , 4A, B View Figure 4 ). The oral primordium widens anteriorly, and the new adoral membranelles start to develop in the anterior portion ( Fig. 4C View Figure 4 ). At the same time, three short streaks separate from the right anterior portion of the oral primordium to form FVT anlagen I–III of the opisthe. Simultaneously, parental cirrus IV/3 dedifferentiates to form anlagen IV–VI of the proter, and cirrus V/4 disaggregates to form anlagen V and VI of the opisthe. The parental cirri III/2 and IV/2 also disaggregate at the same time to form anlagen III of the proter and IV of the opisthe, respectively. The partial reorganization of the undulating membranes commences at the anterior end to form anlage I of the proter, occurring simultaneously with the disaggregation of cirrus II/2 (buccal cirrus) to form anlage II of the proter ( Fig. 4C View Figure 4 ). The six anlagen in each of the proter and opisthe produce 18 cirri, as in other oxytrichid species. The three frontal cirri, two frontoventral cirri VI/3 and VI/4, postoral cirrus V/3, pretransverse cirri V/2 and VI/2, and the five transverse cirri do not participate in the anlagen formation and disappear at the late and very late stages of division ( Fig. 4E View Figure 4 ).

The right marginal anlagen appear at two levels by within-row anlagen formation in the middle stage of division, and the left marginal anlagen appear slightly later. The anterior right marginal anlage arises by the disintegration of the second cirrus and elongates posteriorly using several parental cirri. The posterior right marginal anlage arises slightly posterior to mid-body and extends anteriorly right to the old cirri and posteriorly within the row using a few cirri. The anterior left marginal anlage appears at the anterior end of the parental row and extends posteriorly using two cirri. The posterior left marginal anlage arises within the row and extends posteriorly using a few cirri ( Fig. 4C, E View Figure 4 ).

The dorsal ontogenesis is in the Oxytricha pattern, i.e. kinety 3 anlagen arise in middle dividers ‘within-row’ at two levels, followed by anlagen of kineties 1 and 2 in both the proter and opisthe. In late dividers, anlage 3 fragments in the posterior region, forming anlage 4 in each daughter cell. Two dorsomarginal anlagen develop anterior and right of, and possibly by splitting from, the anterior end of the right marginal anlagen in both the proter and opisthe. A single caudal cirrus is formed at each posterior end of the new dorsal kineties 1, 2, and 4. The nuclear division occurs as in other oxytrichid ciliates ( Fig. 4D, F View Figure 4 ).