Microvilli are light microscopically distinct from filopodia and retraction fibers [ 29].

The latter is quite critical especially to preserve fine and fragile cellular microextensions such as filopodia or retraction fibers [ 15, 16].

We use the term "micropodia" here for morphologically describing filopodia, microspikes, and retraction fibers, and to differentiate these structures from lamellipodia.

While the transiently occurring filopodia and retraction fibers can largely be distinguished only by time-lapse video microscopy [ 22], both, micropodia and lamellipodia, are functionally related to movement of cells.

Filopodia or microspikes extend actively from the cell surface, whereas retraction fibers are extensions that have been left behind by a retracting lamellipodium or that are derived from an attached filopodium.