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

Tintinnid ciliates are traditionally identified by their loricae; however, increasing evidence indicates that some lorica features (e.g. its length, spiraled structures) are not reliable. The vast majority of tintinnids inhabit the marine pelagial; merely, about thirty species live in freshwater. In the present study, two morphotypes with similar lorica shapes and opening diameters but deviating lorica lengths were isolated from freshwater samples collected at different water temperatures near Chongming Island in the Yangtze Estuary, China. The specimens were studied in vivo and after protargol staining, and their phylogenetic placement was inferred from three ribosomal RNA markers; further, cell division was investigated in the short morphotype. Based on the original descriptions, the longer morphotype is identified as Tintinnopsis longa nom. corr. Chiang, 1956, and the shorter one as Tintinnopsis tubuformis Chiang, 1956. Despite distinct differences in the lorica lengths, the identity of the three molecular markers in both morphotypes suggests conspecificity, which is supported by overlapping ranges in the lorica opening diameters and the length-independent features of the somatic ciliary pattern (e.g. number of kineties). Hence, we synonymized T. longa nom. corr. with T. tubuformis and neotypified the later species.