Morphological, Molecular, and Growth Characteristics of a Cryptic Species, Strombidium parasulcatum n. sp. (Alveolata: Ciliophora: Oligotrichida)

A new marine planktonic ciliate from Taiwan, Strombidium parasulcatum sp. n., is described based on live observations, protargol staining, and molecular data. Its morphological characters are similar to those of Strombidium sulcatum Claparède and Lachmann, 1859 sensu Song et al., 2000 but differ from S. sulcatum sensu Fauré-Fremiet, 1912 and sensu Fauré-Fremiet and Ganier, 1970 by several morphological characters. The 18S rRNA gene sequences of the two forms display 76 base pair differences (about 5%), indicating that they should be considered separate species. The highest observed specific growth rates of S. parasulcatum in culture were 1.79 day(–1) over 1 day and 1.52 day(–1) over 2 days, both starting at day 5. Bacteria appear to be an important food resource for the cultivation of this medium-sized oligotrich ciliate. This and other recent studies suggest that cryptic species may be common in the genus Strombidium, and an integrative approach including morphological, ecological, and molecular data should be used to address this question.