Three redescriptions in Tintinnopsis (Protista: Ciliophora: Tintinnina) from coastal waters of China, with cytology and phylogenetic analyses based on ribosomal RNA genes

Abstract

Background: The taxonomy of tintinnine ciliates is vastly unresolved because it has traditionally been based on the lorica (a secreted shell) and it has only recently incorporated cytological and molecular information. Tintinnopsis, the most speciose tintinnine genus, is also the most problematic: it is known to be non-monophyletic, but it cannot be revised until more of its species are studied with modern methods. Results: Here, T. hemispiralis Yin, 1956, T. kiaochowensis Yin, 1956, and T. uruguayensis Balech, 1948, from coastal waters of China, were studied. Lorica and cell features were morphometrically investigated in living and protargol-stained specimens, and sequences of three ribosomal RNA (rRNA) loci were phylogenetically analyzed. The three species show a complex ciliary pattern (with ventral, dorsal, and posterior kineties and right, left, and lateral ciliary fields), but differ in lorica morphology, details of the somatic ciliature and rRNA gene sequences. Tintinnopsis hemispiralis is further distinguished by a ciliary tuft (a ribbon of very long cilia originating from the middle portion of the ventral kinety and extending out of the lorica) and multiple macronuclear nodules. Both T. kiaochowensis and T. uruguayensis have two macronuclear nodules, but differ in the number of somatic kineties and the position of the posterior kinety. Two neotypes are fixed for T. hemispiralis and T. kiaochowensis to stabilize the species names objectively, mainly because of the previous unavailability of type materials. By phylogenetic analysis and comparison with closely-related species, we infer that the ciliary tuft and details such as the commencement of the rightmost kinety in the lateral ciliary field are synapomorphies that may help clarify the systematics of Tintinnopsis-like taxa. Conclusion: The redescriptions of three poorly known Tintinnopsis species, namely T. hemispiralis, T. kiaochowensis, and T. uruguayensis firstly revealed their ciliary pattern and rRNA sequences. This study expands knowledge and database of tintinnines and helps in identifying potential synapomorphies for future taxonomic rearrangements.

Taxonomy and phylogeny of the freshwater tintinnid Tintinnopsis tubuformis Chiang, 1956 (Ciliophora, Oligotrichea) and a proposed synonymization of T. longa nom. corr. Chiang, 1956

“…The other complex somatic ciliary patterns hitherto described deviate by minute features (e.g. the starting point of the ventral kinety, the position of the posterior kinety, and the number of dikinetids in the first right kineties; Agatha, 2008, 2010b; Bai et al, 2020c, d; Wang et al, 2020), which might contribute to the necessary revision of the non‐monophyletic genus Tintinnopsis (Agatha & Strüder‐Kypke, 2007). Note that in contrast to the description of T. cylindrica by Agatha and Riedel‐Lorjé (2006), Coats et al (2010) demonstrated that its pattern is similar to that of Schmidingerella in a ventral kinety composed of a monokinetidal anterior and a dikinetidal posterior portion.…”

“…The total genomic DNA was extracted, using the DNeasy Blood & Tissue kit (Qiagen). The PCR amplification of the SSU rRNA gene and ITS1‐5.8S rRNA gene‐ITS2 regions was performed with the primers 18S‐F (5’–AAC CTG GTT GAT CCT GCC AGT–3′) and 5.8S‐R (5’–TAC TGA TAT GCT TAA GTT CAG CGG–3′) (Bai et al, 2020c; Medlin et al, 1988). The PCR amplification of the LSU rRNA gene was performed with the primers 28S‐1F (5’–ACC CGC TGA ATT TAA GCA T–3′) and 28S‐3R (5’–AAC CTT GGA GAC CTG AT–3′) (Moreira et al, 2007).…”

“…However, only a minor fraction (about 17 species) have been studied regarding their cytological features (e.g. ciliary pattern, nuclear apparatus, and peculiarities of the cell division) (Agatha, 2008, 2010b; Agatha & Riedel‐Lorjé, 2006; Bai et al, 2020b, c, d; Cai et al, 2006; Gruber et al, 2018; Wang et al, 2020, 2021). In phylogenetic analyses, the congeners are disseminated across 12 tintinnid clades often grouping together with taxa possessing hyaline (transparent) loricae (Santoferrara & McManus, 2021).…”