Clevelandella fryntai sp.nov.

(Figs 16–18; Supporting Information, Tables S13, S14)

Description based on populations from SRU hosts from Cambodia: Spade-shaped Clevelandella, size in vivo quite variable 113– 189 × 55–79 µm, usually about 143 × 63 µm; size in protargol preparations 110–167 × 51–82 µm, usually about 130 × 65 µm; dorsoventrally flattened, widest in posterior half of cell, anterior end broadly tapered, cell shape varies depending on host and possibly nutritional status, i.e. morphology less variable within than between hosts, well-fed cells plump (L/W ratio about 2.6), less well-fed cells narrower (L/W ratio about 2.1), cells of intermediate length–width ratio common (range 1.6–2.8). Peristomial projection length relative to cell length quite variable depending on nutritional status (average in all cells about 19%; about 25% in more slender, less well-fed cells; about 17% in plumper, well-fed cells), peristomial overture extends nearly entire length of peristomial projection regardless of nutritional state (Fig. 18A–D). Macronucleus in anterior half of cell, inverted teardrop-shaped (Fig. 17G) to lenticular (Fig. 17B, H), chromatin granular; micronucleus distinctly ellipsoidal (Fig. 17H), adjacent to macronucleus, about 7 × 4 µm. Presence of karyophore highly variable, not seen or quite inconspicuous in vivo, when present, appearance in protargol preparations (Fig. 17G) highly variable (seen at anterior and posterior ends of macronucleus in 11 of 39 cells, anterior end only in 7 of 39 cells, at posterior end only 4 of 39 cells, undetectable in 17 of 39 cells). Swims lazily. Somatic ciliature composed of about 80–100 somatic ciliary rows in Clevelandellidae pattern, about 20–25 ciliary rows extend on to peristomial projection, somatic cilia restricted to approximately anterior two-thirds of cell except for four or five ciliated circumperistomial kineties. Sutural kinetofragments absent. Adoral zone usually extends about 45% of body length, composed of an average of 60 membranelles, base of membranelles longest in posterior one-third of adoral zone. POM as described for the family.

Remarks on phenotypic variability: Two genetically different populations were detected in SRU host: (i) (Fig. 17A) and (ii) (Figs 17B–K, 18). Cells of population (i) were markedly larger than cells of population (ii)—cell size in vivo 180 × 65 µm vs. 141 × 64 µm (Supporting Information, Tables S13, S14).

Based on overall morphology, the cells can be divided into two more or less distinct morphotypes: slender (Figs 16A, 17A, B, G, 18A, B) and broad (Figs 16B–E, 17C–E, H–K, 18C–F). In population (i) only the slender morphotype was detected.

Occurrence: Clevelandella fryntai occurred in all six dissected SRU individuals (all from the same family group). Population (i) was detected in only one individual (subadult female), the very same in which C. sidi (see above) was found. The five remaining hosts harboured population (ii): in four (male, two females, and a larva) of them the slender and broad morphotypes co-occurred and in one (larva) only the slender was present.

Redescriptions of known species of Clevelandellidae

In addition to the newly described species, a number of known species was observed, namely: Anteclevelandella constricta, R. nipponensis, R. hastula, Paraclevelandia brevis, Paraclevelandia simplex, C. elongata, C. parapanesthiae, C. kidderi (weconsider C.lynni Pecina and Vďačný, 2020 as a junior synonym of C. kidderi, see discussion), and C. panesthiae . Most, but not all available ciliate populations were morphologically characterized. For known species, except C. elongata, which has not been reported since its original discovery by Kidder (1937), descriptions are limited to those characters not previously reported, previously recorded inaccurately (e.g. somatic ciliature), or deviating significantly from previous descriptions. Apart from them, two species were detected but left undescribed, namely: Rhynchoclevelandella sp. 2 and Clevelandella sp. 4 . The hosts infected and the occurrence of individual species are summarized inSupporting Information, Table S48.