Phylogeny and Genetic/Morphological Variation of Strombidinopsis minima-like Species (Ciliophora: Choreotrichia).

Six isolates of mineral-enveloped Strombidinopsis minima-like species were collected from the coastal waters across several regions in Korea. Morphological observations and molecular analyses were performed. The ribosomal DNA sequences (including small subunit ribosomal DNA, internal transcriber spacer 1-5.8S ribosomal DNA-internal transcriber spacer 2; and part of large subunit ribosomal DNA) of these six isolates were compared. Their morphological characteristics were also compared with those of S. minima populations reported. The marked genetic differences (with a similarity range of 96.85-98.48%) in SSU rDNA among these S. minima-like entities suggest the existence of multiple species. This finding is also supported by morphological variations detected in this study and reported in the literature (e.g. 15-32 collar membranelles in different populations). In addition, S. minima-like species are clustered with S. batos and S. sinicum, and therefore, our SSU rDNA results support previous results suggesting that the genus Strombidinopsis is not monophyletic in origin. Further collection of morphological and molecular data may facilitate the determination of a new genus carrying mineral-enveloped Strombidinopsis species.