Cyrtohymena seorakensis, Omar & Jung, 2020

Omar, Atef & Jung, Jae-Ho, 2020, Morphology and Molecular Phylogeny of the Soil Ciliate Cyrtohymena seorakensis sp. n. (Ciliophora, Hypotricha, Oxytrichidae), Zootaxa 4758 (3), pp. 561-572 : 567-568

Comparison of Cyrtohymena seorakensis sp. n. with its congeners

( Table 2)

Up to date, the genus Cyrtohymena contains ten species including C. seorakensis sp. n. Based on the body size, the color of cortical granules, and morphometric data, our new species is closely related to C. citrina and C. primicirrata .

Cyrtohymena citrina can be distinguished from C. seorakensis sp. n. mainly by the number of transverse cirri (5 vs. 4), the number of the adoral membranelles (34 vs. 28 on average), and the arrangement of cortical granules (around dorsal bristles and cirri vs. randomly scattered). Other minor differences include the body shape (both ends

broadly rounded vs. posterior end narrower than anterior) and the total number of dorsal bristles (~73 as calculated from the hand drawing of Berger & Foissner 1987 vs. 53–73). The Indian population of C. citrina described by Singh & Kamra (2015) is slightly smaller than C. seorakensis sp. n., has higher number of dorsal bristles (81–111 vs. 53–73), and, interestingly, a larger cyst size (~ 40 μm vs. 18–20 μm). In terms of their higher genetic similarity (i.e., 1 nt difference), our data supports that the SSU rRNA gene is insufficient to discriminate closely related species; we can find species differs in a single nucleotide from its congener (for Pleurotricha see Park et al., 2017, for Stylonychia see Schmidt et al., 2006a, 2006b).

Cyrtohymena primicirrata is also similar to C. seorakensis sp. n., i.e., in the body size, the number of the marginal cirri, and the color of the cortical granules. However, they differ mainly in the number (5 vs. 4) and location (displaced anteriad vs. posteriad) of transverse cirri, the arrangement (around cirri and dorsal bristles vs. randomly scattered) of cortical granules, the number of dorsal bristles (~86 vs. ~62), and the length of the dorsal kinety 4 (long vs. distinctly shortened anteriorly) ( Foissner, 1984).

The type species C. muscorum is unique in having red cortical granules and thus can be easily distinguished from C. seorakensis sp. n. The other six Cyrtohymena spp. are very poorly known and lack detailed description, and thus possibly some of them are synonyms or belong to different genera as noted by Berger (1999). However, all of them are similar to C. seorakensis sp. n. in the body size, but four of them, namely C. aestuarii ( Margalef López, 1945) Berger, 1999 , C. torrenticola ( Ŝrámek-Huŝek, 1957) Foissner, 1989 , C. sapropelica ( Kahl, 1932) Foissner, 1989 , and C. granulata ( Kahl, 1932) Foissner, 1989 , lack cortical granules. Further, C. marina ( Kahl, 1932) Foissner, 1989 has inconspicuous cortical granules and marine habitat, and C. gracilis ( Kahl, 1932) Foissner, 1989 has brownish cortical granules. Moreover, all of these species, except C. aestuarii , have five transverse cirri ( Table 2).