Morphological, Phylogenetic and Ecophysiological Characterization of a New Ciliate, Platynematum rossellomorai n. sp. (Oligohymenophorea, Scuticociliatia), Detected in a Hypersaline Pond on Mallorca, Spain

The Diversity Patterns of Rare to Abundant Microbial Eukaryotes Across a Broad Range of Salinities in a Solar Saltern

Solar salterns are excellent artificial systems for examining species diversity and succession along salinity gradients. Here, the eukaryotic community in surface water of a Korean solar saltern (30 to 380 practical salinity units) was investigated from April 2019 to October 2020 using Illumina sequencing targeting the V4 and V9 regions of 18S rDNA. A total of 926 operational taxonomic units (OTUs) and 1,999 OTUs were obtained with the V4 and V9 regions, respectively. Notably, most of the OTUs were microbial eukaryotes, and the high-abundance groups (> 5% relative abundance (RA), Alveolata, Stramenopila, Archaeplastida, and Opisthokonta) usually accounted for > 90% of the total cumulative read counts and > 80% of all OTUs. Moreover, the high-abundance Alveolata (larger forms) and Stramenopila (smaller forms) groups displayed a significant inverse relationship, probably due to predator-prey interactions. Most of the low-abundance (0.1-5% RA) and rare (< 0.1% RA) groups remained small portion during the field surveys. Taxonomic novelty (at < 90% sequence identity) was high in the Amoebozoa, Cryptista, Haptista, Rhizaria, and Stramenopila groups (69.8% of all novel OTUs), suggesting the presence of a large number of hidden species in hypersaline environments. Remarkably, the high-abundance groups had little overlap with the other groups, implying the weakness of rare-to-prevalent community dynamics. The low-abundance Discoba group alone temporarily became the high-abundance group, suggesting that it is an opportunistic group. Overall, the composition and diversity of the eukaryotic community in hypersaline environments may be persistently stabilized, despite diverse disturbance events.

Phylogenetic Position of Three Well-known Ciliates from the Controversial Order Loxocephalida Jankowski, 1980 (Scuticociliatia, Oligohymenophorea) and Urozona buetschlii (Schewiakoff, 1889) with Improved Morphological Descriptions

Loxocephalids represent a nonmonophyletic assemblage of oligohymenophorean ciliates with morphological features common to both scuticociliates (mode of ontogenesis) and hymenostomes (morphology of the oral structures). In phylogenetic analyses that include both nuclear and mitochondrial molecular markers, relationships among loxocephalid ciliates are still largely unresolved. With the aim to clarify the phylogeny of the controversial order Loxocephalida Jankowski, 1980, we provide the first 18S rRNA gene sequences of three morphologically well-described ciliates currently included in the order, namely Cinetochilum margaritaceum, Zitheron hovassei, and Zitheron muscorum comb. nov. We also provide the first 18S rRNA gene sequence for the monotypic genus Urozona. Here we present improved diagnoses for these species based on updated morphologic data. Our molecular data circumscribe the family Cinetochilidae Perty, 1852 and support the exclusion of genus Cinetochilides from family Cinetochilidae; therefore, we establish a family Cinetochilididae fam. nov. We consider Urozona as incertae sedis in Oligohymenophorea at the current state of knowledge.