Archaeal hooks are difficult to distinguish from the filament; they also
tend to be longer than bacterial hooks. A basal body has not
been identified, but some preparations of archaeal flagella have a
knoblike structure at the end embedded in the cell. One interesting
feature of the flagellar proteins thus far characterized is that
they are more related to type IV bacterial pili than they are to the
proteins in bacterial flagella. Like type IV pili, the filament of the
archaeal flagellin increases in length as flagellin subunits are
added at the base.