The myoneme of the Acantharia (Protozoa): A new model of cellular motility.

The myonemes of Acantharia are made of bundles of microfilaments twisted up in elementary microstrands of two. Myonemes exhibit three kinds of movements: slow contraction accompanied by undulations of the organelle, quick contraction and subsequent relaxation. In vivo, contraction-relaxation cycles were studied with normal, time-lapse and high speed film-recordings (1000 frames/s). Kinetic parameters of these movements are given. All the movements are actively produced by the organelle itself and are dependant on calcium concentration. An hypothesis about the way myoneme microfilaments might interact to generate motile forces is given. The most closely related system might be the myoneme of the dinoflagellate Noctiluca miliaris.