Revision of Strombidium paracalkinsi (Ciliophora: Oligotrichea: Oligotrichia), with Comparison of Strombidiids Bearing Thigmotactic Membranelles

Abstract

This study analyses the morphological characters of Strombidium paracalkinsi, a species bearing thigmotactic membranelles, collected from Jangmok Bay at the southern coast of Korea. The small subunit ribosomal RNA gene of S. paracalkinsi was sequenced for the first time. By a combination of characters, the thigmotactic membranelles of S. paracalkinsi differ from the thigmotactic membranelles of other strombidiids. They are (1) positioned on dorsal side, (2) contiguous with three membranelles of the adoral zone, but separated by nonciliated portions of the polykinetids, and (3) composed of two rows of kinetids. Except for the thigmotactic membranelles, the morphology of S. paracalkinsi conforms to the diagnosis of the genus Strombidium. Our phylogenetic tree confirms the nonmonophyly of the genus Strombidium. The thigmotactic membranelles are a promising feature for a future split of the genus Strombidium, but require further studies, especially on Strombidium calkinsi Fauré-Fremiet 1932.

Keywords: Molecular phylogeny; SSU rRNA; morphology; oligotrichid ciliates.