genus of blue-green algae common in freshwater environments, including hot springs. This unbranched filamentous alga, occurring singly or in tangled mats, derives its name from its slow, rhythmic oscillating motion, which is thought to result from a secretion of mucilage that pushes the filament away from the direction of excretion. Reproduction is by fragmentation in which dead concave cells (separation disks) separate sections of the filament (hormogonia). When present, the mucilage sheath is very thin.