Hidden Species Diversity in Sulfonecta Jankowski, 1978 (Ciliophora: Armophorea): Integrative Evidence for a New Species and Reassessment of the Type Species

Research on anaerobic ciliates has intensified over the past decades, with Armophorea being most studied, but members of Armophorida remaining relatively understudied. Previously, the genus Sulfonecta Jankowski, 1978 was monotypic, with S. uniserialis (Levander, 1894) Jankowski, 1978 as the type species. Our morphological and molecular investigation of two Korean populations of freshwater caenomorphid ciliates identified S. uniserialis from Jeju and a new species, S. multiserialis n. sp., isolated from Ulsan. The new species is characterized by one to three macronuclei and a pronounced expansion of the posterior region, with posterior kineties (PK) comprising 7-11 rows, each row possessing more than 25 dikinetids. We consider populations previously reported by Schmall (1976) and Foissner et al. (1992) as S. uniserialis to be synonymous with the new species. By contrast, S. uniserialis has a more slender posterior region bearing only 3 or 4 PK. The separation of Sulfonecta multiserialis n. sp. and S. uniserialis is also supported by clear phylogenetic divergence. Their SSU rRNA gene sequences differ by 22-34 nucleotides, reinforcing recognition of two distinct species within Sulfonecta.