Dysteria monostyla (Ehrenberg, 1838) Kahl, 1931

(Fig. 5 A–E; Table 2)

Morphological description. Body 40–70 × 30–45 µm in vivo, rectangular to oval in side view (Fig. 5A). Two ventrally located contractile vacuoles, one at anterior 1/3 and the other at posterior 1/4 of cell, each with a diameter of about 4 μm and a pulsating interval of about 15 s (Fig. 5A). Two nematodesmal rods, each about 25 μm long. Macronucleus ellipsoidal and heteromerous, about 25 × 15 μm in vivo and about 25 × 13 μm after protargol staining (Fig. 5E). Micronucleus not detected. Podite about 12 µm long. Cell surface densely covered by bar-shaped ectosymbiotic bacteria (about 4 μm long; Fig. 5B). Fine transverse stripes at mid-body on surface of both lateral plates (Fig. 5B).

Invariably five right kineties with densely arranged basal bodies including two frontoventral kineties with 119–128 basal bodies each (Fig. 5C). Five to eight left kineties (Fig. 5E). Terminal fragment consists of 9–11 basal bodies (Fig. 5C). Equatorial fragment composed of 5–19 kinetosomes (Fig. 5C). Oral apparatus typical of genus (Fig. 5D).

SSU rRNA gene sequence and phylogenetic position. The GenBank accession number, length, and G + C content are MK 882888, 1,677 bp, and 44.25%, respectively. The closest related Dysteria species is Dysteria compressa (KC 753491) with a 99.8% sequence similarity. In phylogenetic trees (Fig. 6), D. monostyla first groups with D. compressa KC753491, then clusters with D. brasiliensis FJ870067 with high support values (ML /BI, 99%/1.00).