Lepidometopus platycephalus, Vď’Ačný & Foissner, 2017

Vď’Ačný, Peter & Foissner, Wilhelm, 2017, A Huge Diversity of Metopids (Ciliophora, Armophorea) in Soil from the Murray River Floodplain, Australia. II. Morphology and Morphogenesis of Lepidometopus platycephalus nov. gen., nov. spec., Acta Protozoologica 56 (1), pp. 39-57 : 41-47

Lepidometopus platycephalus nov. spec. Foissner and Vďačný

Diagnosis: Size about 45 × 20 µm in vivo. Body broadly to narrowly reniform with a somewhat rhomboid appearance when viewed ventro- or dorsolaterally. Macronucleus between anterior and posterior end of adoral zone, globular to oblong; one globular to broad- ly ellipsoid micronucleus. Contractile vacuole terminal. Epicortical scales about 1.25 × 0.45 µm in SEM, flat with margin curled up. On average 11 ciliary rows; caudal cilium about 20 µm long. Perizonal stripe com- posed of five kineties extending approximately 46% of body length and forming about 19 false kineties. Adoral zone extends about 50% of body length, composed of an average of 11 polykinetids.

Type locality: Loamy soil and leaf litter from the floodplain of the Murray River near to the town of Al- bury, Australia (S36°06' E146°54') .

Type material: The holotype slide and eight paratype slides with protargol-impregnated specimens have been deposited in the Museum of Natural History (Bi- ologiezentrum) in Linz (LI), Austria. The holotype ( Fig. 2K, L) and relevant paratype specimens as well as dividers have been marked by black ink circles on the coverslip .

Etymology: Derived from the Ancient Greek adjec- tive platús (πλατύς, flat) and the Ancient Greek noun képhalos (κέφ ᾰ λΟς [m], head), referring to the strongly flattened preoral dome. The composite name is latinized and treated as a noun in the nominative singular standing in apposition to the generic name [Art. 11.9.1.2 of the International Commission on Zoological Nomen- clature (1999)].

Description: Size in vivo 35–50 × 15–30 µm, usu- ally about 45 × 20 µm, as calculated from some in vivo measurements and the morphometric data adding 15% preparation shrinkage ( Table 1). Body asymmetric and thus multi-shaped: broadly to narrowly reniform in ventro- and dorsolateral views ( Figs 2A, G, K–V, 3A, B, 4C, D), broadly crescentic in lateral views ( Figs 2F, H, 4B, E, 5B), and dumbbell-shaped in ventrocaudal views ( Figs 2I, 5C); body ends somewhat angular providing cells with a rhomboid or triangular appearance, depending on observation perspective; distal portion of preoral dome strongly flattened and thus hyaline, only 2–3 µm thick in vivo ( Fig. 3A–C, asterisks), projects distinctly in lateral views, forming a right or nearly right angle with main body axis ( Fig. 4B, E, opposed arrowheads); postoral body portion unflattened and usually distinctly vaulted ( Figs 4A–E, 5B, C). Localization of nuclear ap- paratus very stable, i.e., between anterior and posterior end of adoral zone and left of cell’s midline. Macro- nucleus broadly ellipsoid (52.4%), ellipsoid (23.8%), narrowly ellipsoid (9.5%) or globular (14.3%), i.e., length:width ratio 1.0–5.0:1, size about 8–20 × 4–9 µm, usually 12 × 7 µm in protargol preparations; nucleoli 0.5–1 µm across. Micronucleus usually attached to an- terior portion of right margin of macronucleus; shape and size rather stable, i.e., globular to broadly ellipsoid and 2–3 µm in diameter after protargol impregnation ( Figs 2A, K, J, M, O–V, 3C, E–H; Table 1). Contractile vacuole in posterior body end, globular to ellipsoid during diastole ( Figs 2A, K, O–Q, S–V, 3A, B, D). Cortex flexible, covered by epicortical scales (lepidosomes) usually forming a 1–2 µm, rarely an up to 4 µm thick layer with slimy or fibro-granular appearance in vivo ( Fig. 3A, C, D, opposed arrowheads) and flake-like ap- pearance in SEM ( Figs 4H, 5A), not recognizable in protargol or silver carbonate preparations. Individual lepidosomes with irregular shape, flat with margin curled up, rather variable in size, viz., 0.50–1.65 × 0.20– 0.80 µm, on average 1.25 × 0.45 µm in SEM ( Figs 2E, 4H, 5A). No cortical granules recognizable. Cytoplasm colourless, contains many 3–6 µm-sized food vacu- oles with bacterial spores; symbiotic bacteria neither detected in vivo nor in protargol preparations ( Fig. 3A). Creeps slowly and ungainly on microscope slides, rotates slowly about main body axis when swimming.

Somatic ciliature composed of dikinetids, anterior cilium lacking in postoral kinetids ( Fig. 4I) except for those extending along left body margin, an unusual feature observed in vivo, after protargol impregnation, and confirmed in SEM ( Figs 2A, 3C, 4B–D, arrows, J). So- matic cilia comparatively widely spaced, rather rigid, in vivo 10–12 µm long in mid-body, up to 13 µm on rear body end; a single elongated caudal cilium with filiform distal end, 16–30 µm long, usually about 20 µm long in vivo, fragile and thus usually missing in prepared specimens ( Figs 2A, 3A, D). On average 11 equidistant and ordinarily spaced ciliary rows, i.e., interkinetal distance about 5–6 µm in protargol preparations, follow body curvature ( Figs 2K–N, 3E, F; Table 1). Perizonal stripe begins at left anterior body margin, extends along whole anterior body end, curves perpendicularly to right anterior margin, and terminates on right margin of dorsal side at or slightly anterior to level of proximal end of adoral zone, i.e., forms a Γ-shaped pattern; extends 46% of body length on average; invariably composed of five rows: first three rows more narrowly spaced than the two last rows with dikinetids slightly shifted, providing stripe with a staggered appearance. Stripe rows segmented into an average of 19 false kineties, each perizonal dikinetid with two cilia 15–18 µm long in vivo and 8–12 µm in SEM; number of perizonal rows often difficult to deter- mine in distal portion of stripe due to their narrow spacing and strong flattening of anterior body portion, but on- togenetic data indicate that there are five rows beginning at almost same level ( Figs 2B, K–N, 3E–H, 4G; Table 1).

Type 4 oral area. Adoral zone extends vertically to strongly obliquely and about half of body length, roofed by preoral dome, composed of an average of 11 polykinetids up to 6 µm wide; cilia 5 µm long in vivo, usually spread backwards in SEM ( Fig. 5D); proxi- mal- and distalmost polykinetids rectangular or somewhat irregular and composed of two to three rows of basal bodies, others L-shaped and usually composed of a short row and three long rows ( Fig. 2C). Paroral membrane begins about 17 µm posterior to anterior body end, extends along right margin of side stripe, optically intersects adoral zone; composed of narrowly spaced, oblique ellipsoids being dikinetids according to the ontogenetic data, only one basal body ciliated according to SEM observations, cilia 3–6 µm long in SEM, form a tongue-like or fimbriate structure ( Figs 2C, L, N, 3G, H, 4F, 5D, E; Table 1). Cytopharyngeal fibres originate from proximal end of adoral zone and paroral membrane, extend backwards forming a funnel about 15 µm long in protargol preparations ( Fig. 2L, N). Dome lip inconspicuous because only 0.25–0.50 µm wide in SEM. Side stripe a comparatively deep, 2.3–3.3 µm wide channel in the scanning electron microscope, covered by epicortical scales ( Fig. 5D, E).