The slipper animalcule is a unicellular organism of the ciliate family

The slipper animalcule is very spectacular owing to:
a) its form
b) the hair-like filaments (for locomotion and directing food into its mouth)
c) the fact that it can navigate rather well

so, as it is an entry-level model in the field of micro-organisms there are still a whole lot of interesting motives.