Laboea coronata, Agatha, 2014

Agatha, Sabine, 2014, Redescription of Strombidium coronatum (Leegaard, 1915) Kahl, 1932 (Ciliophora, Spirotricha) based on live observation, protargol impregnation, and scanning electron microscopy, Acta Protozoologica 53 (4), pp. 287-294 : 288-292

Strombidium coronatum ( Leegaard, 1915) Kahl, 1932

1915 Laboea coronata n. sp. – Leegaard, Nyt Mag. Naturvid. 53: 13.

1932 Strombidium (Laboea) coronatum ( Leegaard, 1915) – Kahl, Tierwelt Dtl. 25: 500 (combining author; revision).

1985 Strombidium coronatum ( Leegaard, 1915) Kahl,

1932 – Maeda and Carey, Bull. Ocean Res. Inst.,

Univ. Tokyo 19: 46 (revision).

1988 Strombidium coronatum (Leegard, 1915) Kahl,

1932 – Laval-Peuto and Rassoulzadegan, Hydrobiologia 159: 104 (epifluorescence microscopy; incorrect spelling of original author’s name). 2005 Strombidium sp. – Gismervik, Aquat. Microb.

Ecol. 40: 164 (growth and feeding rates).

2008 Strombidium choronatum – Claessens, Wickham, Post and Reuter, Aquat. Microb. Ecol. 53:

186 (incorrect subsequent spelling of specific epithet).

Remarks: Since the original description did not provide a diagnosis, the distinguishing features are given here based on the type and neotype populations.

Diagnosis (based on type and neotype populations): Size in vivo ~ 45 × 25 µm, after preservation ~ 40–86 × 24–53 µm; obconical, with collar-shaped apical protrusion and peculiarly flattened peristome extending in sagittal plane. Macronucleus and micronucleus usually globular. Girdle kinety equatorial, ostensibly continuous, composed of ~ 100 dikinetids. Ventral kinety extends longitudinally on posterior fifth of cell, composed of about five dikinetids. Adoral zone of membranelles widely open, composed of ~ 18–20 collar and ~ 12 buccal membranelles; collar portion disconnected from buccal portion.

Type locality: The species was discovered in the pelagial of the Skagerrak , North Atlantic , near the village of St. Arendal in Norway ( Leegaard 1915). The neotype is from the pelagial of the Irish Sea near the Isle of Man (54°05′06″N, 04°45′50″W), United Kingdom (this study) .

Description of neotype population from the Irish Sea ( Figs 4–21; Table 1): Size in vivo 35–55 × 20–35 µm (calculated from some measurements of live specimens and values shown in Table 1, assuming a shrinkage of ~ 10% due to the preparation procedure), after protargol impregnation 32–48 × 18–30 µm. Shape roughly obconical, i.e., posterior cell half obconical with rounded end, shape of anterior cell half depends on the side viewed: in right lateral view, roughly triangular with inconspicuous projection at top of buccal lip ( Fig. 12); in ventral view, flat peristome separates as sagittal plane vaulted right half from a dorsoventrally inclined left half ( Fig. 9); in left lateral view, buccal portion of adoral zone extends on an anti-clockwise inclined shelf more or less perpendicular to the plane, roughly triangular peristome ( Figs 4, 10, 17, 19 ); and in dorsal view, anterior end slants leftwards ( Fig. 11). Apical protrusion up to 4 µm high after protargol impregnation, collar-shaped, increases in height from distal end of collar zone portion to buccal lip, where it often forms a ventrally directed rectangular projection ( Figs 5, 6, 9, 11, 12, 17, 21 ). Macronucleus in anterior cell half, 8–17 × 8–13 µm in size after protargol impregnation, globular to broadly ellipsoidal, with nucleoli ~ 1 µm across ( Figs 5, 21 ). Micronucleus near macronucleus, 1–1.5 µm across after protargol impregnation ( Fig. 5). Contractile vacu- ole and cytopyge not recognizable. Extrusomes insert in a 1.5–2 µm wide stripe directly anteriorly to girdle kinety, form oblique rows with about four attachment sites each, closely spaced, not clustered ( Figs 4, 17, 18 ); individual extrusomes in vivo ~ 15–20 × 0.5–0.7 µm in size and acicular ( Fig. 4), after protargol impregnation only ~ 7–8 µm long and deformed. Extrusome ejection caused by fixation for scanning electron microscopy ( Fig. 17 ). Cytoplasm colourless, contains food vacuoles with unidentifiable content ~ 3 µm across and occasion- ally frustules of pennate diatoms ~ 25 × 4 µm in size and centric diatoms ~ 5 µm across. Cell surface posterior to girdle kinety (hemitheca) with several longitudinal ridges in preserved specimens, i.e., distinct ridges extend between girdle kinety and posterior cell end, between each pair about three posteriorly shortened, indistinct ridges ( Figs 5, 6, 16–18 ); polygonal cortical platelets not recognizable. Often, cell surface distinctly distended in protargol-impregnated specimens ( Figs 5, 6, 19, 21 ). Swims in narrow spirals by rotation about main cell axis interrupted by rapid changes in direction ( Fig. 14). Somatic cilia ~ 1 µm long in vivo. Girdle kinety equatorial, horizontally orientated, ostensibly continuous, and composed of ~ 100 (inferred from their number per 5 µm of circumference) obliquely orientated dikinetids, each has a cilium associated only with the left basal body ( Figs 5, 6, 16–18 ). Ventral kinety extends longitudinally posterior to buccal vertex on rear fifth of cell, composed of 4–6 dikinetids, each has a cilium associated only with the anterior basal body ( Figs 4, 5, 17, 18, 20, 21 ). Adoral zone of membranelles occupies anterior cell portion, widely open ( Figs 4–8, 16, 17 ). Collar zone portion with “crown-like” appearance (specific epithet derived from Latin noun corona), arranged in a semi-circle disconnected from buccal portion, distinctly slanted leftwards on semi-globular right anterior cell portion and especially on dorsal side, composed of 16–19 membranelles. Collar membranelles triangular, up to 15–20 µm long in vivo, with cilia decreasing in length from distal to proximal end of membranelles; polykinetids comprise three rows of basal bodies ~ 6 µm long, separated by intermembranellar ridges. Buccal zone portion extends on an oblique shelf more or less perpendicularly to the plane peristome, terminating ~ 45% posteriorly to the apical cell end, composed of 9–14 almost rectangular membranelles with cilia up to 7 µm long in vivo; structure of membranelles not recognizable. Endoral membrane not clearly seen in protargol preparations ( Figs 5, 7) and not recognizable in scanning electron micrographs as probably covered with perilemma, extends near ventral margin of peristome. Pharyngeal fibres not recognizable.

Data about ontogenesis base on some early dividers and one late early division stage. Oral primordium develops in transient subsurface tube posterior to girdle kinety and left of ventral kinety ( Figs 13, 20 ). Opisthe’s adoral zone achieves uncommon shape and orientation in late early divider ( Figs 13, 15): it is inversely L-shaped and longitudinally orientated, performing a ~ 180° turn in the unusually elongated posterior cell half. Position of new endoral membrane untypical because distinctly apart from proximal end of opisthe’s adoral zone ( Fig. 13). Girdle kinety and stripe of extrusome attachment sites with gap in left half of ventral side.

Figures

Figs 16–21. Strombidium coronatum, Irish Sea specimens (16–18, scanning electron micrographs; 19–21, protargol impregnation, micro- graphs of several focal planes were stacked, using the computer program CombineZP from Alan Hadley). 16 – ventrolateral view; 17 – left lateral view showing uniquely shaped peristome, which is roughly triangular in outline and almost flat, extending in the sagittal plane. The extrusomes insert in short oblique rows anteriorly to the girdle kinety; note that some of them are just ejected (arrowhead); 18 – posterior cell portion showing the sharp, longitudinal ridges that have already been illustrated in the original description by Leegaard (1915); 19 – left lateral view of an early divider; 20 – dorsolateral view of an early divider; 21 – ventrolateral view. AP – apical protrusion, BM – buccal membranelles, CM – collar membranelles, DC – distended cell surface, EX – extrusome attachment sites, GK – girdle kinety, MA – macro- nucleus, OP – oral primordium, VK – ventral kinety. Scale bars: 40 µm (16), 20 µm (17, 19–21), and 10 µm (18).