A group of Spirostomum, among the largest ciliates which can grow to several millimeters in length, swimming past camera. These wormlike protozoa move by beating hairlike cilia that cover their bodies and which can barely be seen along their outer edges. One of the remarkable things about Spirostomum is its ability to contract suddenly, as it does here at about the 5 second mark. This occurs in less than 8 milliseconds, which is the fastest contraction known in any living cell. Individuals swimming in a group often appear to contract in unison, but it is the contraction of one that triggers the others a split-second later. Recorded under Nomarski DIC illumination.