Movement generated by interactions between the dense material at the ends of microtubles and non-actin-containing microfilaments in Sticholonche zanclea.

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Abstract
Axopods of the planktonic protozoan Sticholonche are used as oars to propel the organism through seawater. Within each axopod is an organized array of microtubules which inserts into a dense material that assumes the form of the head of a hip joint. This material in turn articulates on the surface of the nucleus. Microfilaments, 20-30 .ANG. in diameter, connect the dense material associated with the microtubules to the surface of the nucleus, and they move the axopod by their contractions. The active phase of the movement may take .apprx. 0.04 s, and the recovery phase between 0.2-0.4 s. The microfilaments are not actin, as based on their small diameter, the lack of decoration with heavy meromyosin, and their ability to coil, spiral or fold during contraction. The use of Thorotrast demonstrated that the cell surface was deeply infolded, extending all the way to the hip joint. There was a specialized membrane system that resembled the diad in skeletal muscle. Cytochemical tests and the use of ionophores and chelators, showed some evidence that the motile process may be controlled by Ca. In at least 1 system, microtubules can be moved by contractile microfilaments attached to the dense material at their tips.