Linking morphology and molecules: integrative taxonomy of spathidiids (Protista: Ciliophora: Litostomatea) from Korea

We isolated seven spathidiids from various terrestrial habitats in Korea: Enchelys megaspinata sp. nov.; Spathidium ascendens Wenzel, 1955; S. papilliferum Kahl, 1930; S. polynucleatum (Foissner et al., 2002) comb. nov.; S. rectitoratum Kahl, 1930; S. securiforme Kahl, 1930 stat. nov.; and Apobryophyllum schmidingeri Foissner and Al-Rasheid, 2007. Their vegetative and resting cyst morphology were studied in vivo and after protargol impregnation. Their phylogenetic relationships were inferred from the analysis of 18S rRNA gene and ITS1-5.8S-ITS2 region sequences. Enchelys megaspinata is nested within the Semispathidium breviarmatum cluster. It differs from all multi-macronucleate congeners either by the number of macronuclear nodules and ciliary rows or by the presence of prominent spines on resting cysts. Both morphological and molecular data support species-level status for S. rectitoratum and S. securiforme. Although S. papilliferum is one of the morphologically most distinct spathidiids due to the presence of oral bulge papillae, it is non-monophyletic. Based on molecular analyses, we suggest reassigning the morphologically transitional S. ascendens and S. polynucleatum, both formerly combined with Epispathidium, to the genus Spathidium. Korean and German populations of Apobryophyllum schmidingeri are highly similar, both morphologically and genetically. The present study highlights the complexity of spathidiid taxonomy, which requires a combination of morphological and molecular approaches to resolve.

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