Bioacoustics of Euplotes nobilii

Remarks. The Korean population corresponds well with the type population ( Valbonesi and Luporini, 1990a ), although one outlier specimen from the Korean population showed a slightly higher number of adoral membranelles (i.e., 29 adoral membranelles) than the type population (19-23 vs. 18-22). Compared to other species in the genus, E. rariseta Curds et al. , 1974 highly resembles E. nobilii , but it differs from the latter by the number of dikinetids in the middle kinety (maximum 6 vs. 6-9) ( Curds et al. , 1974 ; Valbonesi and Luporini, 1990a ). However, the description of the morphometric features of the dorsal kinety of E. rariseta has experienced some variation since it was originally described, to include variability among populations, i.e., (number of dorsal kineties/number of dikinetids on mid-kinety) 5/maximum 6 ( Wilbert and Kahan, 1981 ), 6/5-7 ( Kim and Lee, 2019 ), 7/7 ( Dallai et al. , 1987 ), 7/5-7 ( Song and Packroff, 1997 ; Ma et al. , 2007 ), 7/8-10 ( Valbonesi and Luporini, 1990a ). The Antarctic population reported by Valbonesi and Luporini (1990a) might be new to science, as already mentioned by the authors, because it has more adoral membranelles than the others: 28-30 vs. 23 (as seen in the original line drawings of the type population in Curds et al. , 1974 ), 22±2 ( Dallai et al. , 1987 ), 17-21 ( Song and Packroff, 1997 ), 17-22 ( Ma et al. , 2007 ). Unfortunately, phylogenetic analyses based on small subunit ribosomal DNA (SSU rDNA), do not provide enough resolution to discriminate among species of Euplotes . Thus, E. nobilii and E. rariseta (GenBank accession numbers KC599234 and AF492706, respectively) cluster together as almost similar species according to the SSU rDNA phylogeny ( Lian et al. , 2021 ). In contrast to the limited resolution provided by the SSU rDNA gene to identify cryptic species, mitochondrial cytochrome c oxidase subunit I gene ( CO1 ) has been proved as a valuable barcode to distinguish among cryptic species with identical SSU rDNA regions ( Quintela-Alonso et al. , 2013 ), because it has a distinct ‘barcode gap’ between maximum intra-specific and minimum inter-specific divergences ( Park et al. , 2019 ). Voucher slides. One slide with protargol-impregnated specimens (NNIBRPR25657) and one slide with wet silver nitrate-impregnated specimens (NNIBRPR25658) were deposited at the Nakdonggang National Institute of Biological Resources.