Spathidium ascendens Wenzel, 1955

Jang, Seok Won, Vďačný, Peter, Shazib, Shahed Uddin Ahmed & Shin, Mann Kyoon, 2017, Linking morphology and molecules: integrative taxonomy of spathidiids (Protista: Ciliophora: Litostomatea) from Korea, Journal of Natural History 51 (17 - 18), pp. 939-974 : 947-951

Spathidium ascendens Wenzel, 1955

( Figures 3 (a–m) and 4(a–m); Table 2)

Spathidium ascendens Wenzel, 1955: 515 , Abb. 1–8

Epispathidium ascendens – Foissner, 1987b: 231, Abb. 10a–I (description of Austrian populations, combination with Epispathidium )

Description of a Korean population

Body size 130–155 × 20–30 µm in vivo, usually about 145 × 25 µm; not contractile but very flexible. Shape narrowly to very narrowly spatulate with a length:width ratio of 5.1–6.6: 1 in vivo and 3.6–7.6:1 after protargol impregnation; oral region indistinctly set off from cylindrical trunk because neck only slightly narrowed; anterior body end as wide as or slightly narrower than mid-body; posterior end rounded ( Figures 3 (a,h–m) and 4(a,b,d,i); Table 2). Nuclear apparatus in trunk, distance from anterior body end comparatively stable (about 20–30 µm). Macronucleus a filiform strand, coiled at both ends, highly variable in length (i.e. ranging from 50 µm to 155 µm; Table 2); nucleoli small- to medium-sized, globular, evenly distributed over macronucleus, easily recognisable in protargol impregnation. Micronuclei near or attached to macronucleus at varying positions; exact number difficult to determine due to similar-sized cytoplasmic globules ( Figures 3 (a,h–l) and 4(i, m)). A single contractile vacuole at posterior body end, about 10 µm across during diastole ( Figures 3 (a) and 4(a,b)). Extrusomes attached to oral bulge and scattered throughout cytoplasm: oral extrusomes rod-shaped, straight or curved and with rounded ends, 5–8 × 0.5 µm in size, impregnate faintly with the protargol method used; cytoplasmic developing extrusomes fusiform and impregnate deeply ( Figures 3 (c,d) and 4(d,f,l,m)). Cortex very flexible, distinctly furrowed by ciliary rows; contains three or four oblique granule rows between adjacent kineties; granules ordinarily or sometimes loosely spaced, comparatively small (i.e. about 0.5 µm across); cell covered with epibiotic, rod-shaped bacteria 1–2 µm long ( Figures 3 (b) and 4(g,h)). Cytoplasm colourless, contains developing extrusomes and some lipid droplets about 1–2 µm across. Movement relatively slow, either gliding on microscope slide or swimming by rotation about main body axis.

Cilia about 8 µm long in vivo, spaced ordinarily except for three to seven densely spaced cilia in curved anterior kinety portion. On average 19 equidistant, ordinarily spaced meridional ciliary rows anteriorly curved distinctly dorsally on right side while only slightly ventrally on left side ( Figures 3 (f,g,l,m) and 4(j,k); Table 2). Dorsal brush inconspicuous because only about 2.5 µm high in vivo; dikinetal; three-rowed; isostichad (i.e. length difference between shortest and longest rows less than 20%); dikinetids ordinarily spaced and bearing only slightly inflated bristles ( Figures 3 (g,m) and 4(e,k)).

Oral bulge occupies slightly to ordinarily oblique anterior body end, distinctly set off from body proper, conspicuously thickened at ventral and dorsal ends, concave in central area. Circumoral kinety at base of oral bulge, continuous, composed of narrowly spaced and perpendicularly oriented dikinetids associated with fine nematodesmata, forming a funnel-shaped basket recognisable in some protargol-impregnated specimens ( Figures 3 (a,f,g) and 4(a,d,j,k)).

Resting cysts

Cysts colourless, about 25–40 µm across in vivo; without escape apparatus. Cyst wall inconspicuous because smooth and only 1–2 µm thick; covered by a fine mucous layer containing bacteria and some debris particles. Cytoplasm packed with innumerable granules. Macronucleus extends through cyst, strongly shortened, strand-like with thickened ends. Contractile vacuole, extrusomes, cortical granules, and cilia not recognisable ( Figures 3 (e) and 4(c); Table 2).

Comparison with original description and remarks

The Korean population resembles the type population described by Wenzel (1955) as well as Austrian populations described by Foissner (1987b) in the narrowly to very narrowly spatulate body with thickened ends of the oral bulge, filiform macronuclear

strand, and rod-shaped extrusomes. Moreover, Korean and type specimens have a similar number of ciliary rows and produce resting cysts with a smooth wall. However, Austrian specimens differ from Korean individuals by the slightly higher number of ciliary rows (20–25 vs 17–21) and by the more distinctly curved ends of the left side ciliary rows. Unfortunately, Wenzel (1955) did not study the oral ciliary pattern in detail. We prefer Spathidium as the home for S. ascendens , because its oral ciliary pattern is more Spathidium - than Epispathidium -like and because it clusters with other Spathidium species in molecular phylogenies (see below).