Abstract
BackgroundThe 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.ResultsHere, 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 originated 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.ConclusionThe redescriptions of three poorly known Tintinnopsis species, namely T. hemispiralis, T. kiaochowensis, and T. uruguayensis firstly revealed their ciliary patterns and rRNA sequences. This study expands knowledge and database of tintinnines and helps in identifying potential synapomorphies for future taxonomic rearrangements.
Highlights
The taxonomy of tintinnine ciliates is vastly unresolved because it has traditionally been based on the lorica and it has only recently incorporated cytological and molecular information
The present study investigates the morphology and molecular phylogeny of three Tintinnopsis species, namely, T. hemispiralis Yin, 1956, T. kiaochowensis Yin, 1956, and T. uruguayensis Balech, 1948, which were collected from coastal waters of China
Terminology Tintinnopsis hemispiralis possesses a cluster of extremely long cilia that has only been reported for Tintinnopsis subacuta [50]
Summary
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. Tintinnine ciliates are conspicuous due to the diversity of loricae produced by their cell propers. The current lorica-based taxonomy does not allow estimating tintinnine diversity accurately, and it does not provide a natural classification. Cell characters and DNA sequences are only known for about 3 and 10% of the described tintinnine morphospecies, respectively (e.g., [22, 37]), and considerable efforts are needed to increase the availability of these types of information
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