Morphology and in situ sedimentation of the cysts of a planktonic oligotrich ciliate, Strombidium capitatum

The cysts of the oligotrich ciliate Strombidium capitatum isolated from the natural sediments in Onagawa Bay, Japan, and Masan Bay, Korea, were described and incubated to produce, vegetative cells. The vegetative cells that were obtained were observed after protargol staining and with a scanning microscope and then described. The cysts of S. capitatum were spherical with a papula and spiny surface. Their size varied from 55 to 62 mu m in total length and from 45 to 55 pm in width. Seasonal changes in the vegetative population and in sedimentation of the newly formed cysts were investigated in situ in both bays. Planktonic vegetative cells peaked in autumn (December) in Onagawa Bay and in spring (April) in Masan Bay, when water temperature was ca. 15 degrees C, In contrast, the cells were not detected in either bay in summer. Mass encystment. occurred in March in Onagawa Bay and in November in Masan Bay without coincidence with the peaks in vegetative populations at either locality. These results indicate that S. capitatum is adapted to low and moderate temperatures and aestivates during warm summer.