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

Linking multi-gene and morphological data in the subclass Scuticociliatia (Protista, Ciliophora) with establishment of the new family Homalogastridae fam. nov

Scuticociliatia is one of the most species-rich subclasses in the phylum Ciliophora. The evolutionary relationships among Scuticociliatia groups have long been very unclear due to the homogeneity of morphology and insufficiency of molecular data. With morphological and multi-gene-based molecular data presented here, the evolutionary phylogeny of several Scuticociliatia taxa that were hitherto especially poorly defined is analyzed and discussed. The results indicate: (1) all scuticociliates cluster into two well supported and one poorly supported group, representing three order-level taxa; (2) with the support of both morphological and molecular data, a new family Homalogastridae fam. nov. is proposed in the order Philasterida; (3) Parauronema is formally transferred to Uronematidae and Potomacus is treated as incertae sedis in the order Philasterida, therefore Parauronematidae is proposed to be a junior synonym of Uronematidae; (4) the genus Madsenia and the species Parauronema longum and Pseudocyclidium longum are treated as incertae sedis, while the genus Protophyra should be maintained in the family Ancistridae. In addition, the putative secondary structure of internal transcribed spacer 2 (ITS2) of representative taxa from the three orders of Scuticociliatia are analyzed, and consensus structures and nucleotide composition in each order are exhibited.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-024-00264-8.

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.