Zosterodasys transverses ( Kahl, 1928 ) Foissner et al., 1994

Wang, Lijuan, Zhao, Yuanjun & Gong, Jun, 2012, Resdescription of two synhymeniid ciliates, Chilodontopsis simplex Ozaki & Yagiu, 1941 and Zosterodasys transverses (Kahl, 1928) Foissner et al., 1994 (Alveolata, Ciliophora, Phyllopharyngea), Zootaxa 3167, pp. 45-52 : 50-51

Zosterodasys transverses ( Kahl, 1928) Foissner et al., 1994

( Figs. 5–10 , 19–26 ; Table 1 )

Description of the Korean population. Cell size 160–400 × 80–140 µm in vivo. Cell flexible and non-contractile; shape elliptical to elongate in outline; both ends rounded. Both margins convex with anterior portion slightly projected to left ( Figs. 1, 7 , 19, 21 ). Cell slightly dorsoventrally flattened about 3:2 ( Fig. 6 ). Cyrtos composed of 15– 18 nematodesmal rods ( Fig. 23 ), each about 80 µm long in vivo. Cytostome at anterior 1/5–1/7 of cell length. Cytoplasm colorless, floc-like, with numerous yellowish oil balls (diameter 5–9 µm), food vacuoles (7–8 µm across) and ingested diatoms ( Fig. 20 ). Macronucleus usually elongate, sometimes ovoid, positioned at mid-cell, size about 56–128 × 12–40 µm after protargol impregnation ( Figs. 10 , 25 ). Micronuclei not observed. Many contractile vacuoles, 4–7 µm in diameter, irregularly distributed on ventral side ( Figs. 5, 7 , 21, 24 ). Cilia about 7 µm long in vivo, uniformly distributed on ventral and dorsal surfaces. Numerous fine cortical granules irregularly distributed between ciliary rows ( Fig. 8 ). Movement moderately rapid, swimming or gliding on substrate.

Synhymenium S-shaped, composed of 65–130 dikinetids, located in a conspicuous suture, running obliquely from anterior 1/7 to 1/3 of cell on ventral and dorsal sides, forming a complete cycle around cell ( Figs. 7, 9, 10 , 26 ). In total 105–138 somatic kineties, evenly distributed on both sides. About 20 ventral kineties curving around and anterior to cytostome ( Figs. 9 , 22 ).

Remarks. In 1994, Foissner and colleagues transferred Chilodontopsis transversa Kahl, 1928 into the genus Zosterodasys , and gave a detailed description based on a freshwater form, with considering several Chilodontopsis species as junior synonyms ( Foissner et al. 1994; Kahl 1928). Compared with the freshwater form, except that our population is relatively larger in size (160–400 vs. 130–250 µm in length), and has a larger macronucleus (mean 85 × 42 vs. 37 × 23 µm, estimated from drawings), other important characters (e.g. many contractile vacuoles on ventral side, the numbers of somatic kineties and nematodesmal rods, dikinetids in the synhymenium) are almost identical to each other, which, in our opinion, supports the identification of the species. The 18S ribosomal RNA gene (accession number: EU286812 ) amplified from the marine population described here has been reported in Gong et al. (2009). However, the morphological features of the isolate was lacking. We here also link the morphology to the small subunit ribosomal RNA gene, which may be helpful for future studies, for example, exploring whether the difference in habitats (i.e. marine vs. freshwater) will make them separate species or not.

Figures

FIGURES 1 – 10. Chilodontopsis simplex (1 – 4) and Zosterodasys transverses (5 – 10) from life (1, 2, 5 – 8) and after protargol impregnation (3, 4, 9, 10). (1, 5) Ventral view of a typical individual. (2, 7) Ventral views, showing the cell shape and distribution of contractile vacuoles. (3, 4, 9, 10) Ventral (3, 9) and dorsal (4, 10) views of infraciliature, arrowhead in (10) indicates the dikinetids of synhymenium on dorsal side. (6) Lateral view. (8) A close-up of the ventral side, showing the cortical granules between somatic kineties. CV = contractile vacuole; CVP = contractile vacuole pore; Cyp = cytopyge; Ma = macronucleus; Sy = synhymenium. Scale bars = 40 µm.

FIGURES 19 – 26. Photomicrographs of Zosterodasys transverses from live cells (19 – 22) and after protargol impregnation (23 – 26). (19 – 21) Ventral views, arrows indicate the contractile vacuole on ventral side. (22) A close-up of anterior portion of ventral side. (23, 26) Details of oral area, showing the cytostome (asterisk), nematodesmal rods, and synhymenium. (24) Arrows refer to the contractile vacuole pores on ventral side. (25) Showing the nulcear apparatus. D = diatom; Ma = macronucleus; Mi = micronucleus; N = nematodesmal rods; Sy = synhymenium. Scale bars = 40 µm.