Vorticella is a protist (protozoan) and belongs to the Phyllum
Ciliophora. It is a very interesting, stalked ciliate with an
inverted bell shape. The stalk contains a contractile fibril called
a myoneme. When stimulated, it shortens, causing the stalk to coil
like a spring.
usually anchor themselves to small particles of material however, it
is not uncommon to see them free swimming. When they undergo
fission, they split along the longitudinal axis in a process called
budding. When they finally split apart, one keeps the myoneme and
the other free swims away and grows its own. The main purpose for
the cilia at the top is to sweep food down into the gullet.
are over 100 different species of Vorticella.
some more images 1
a beautiful electron microscope image of one here.
left you see a close up of the myoneme in action. This was taken
with phase contrast. Above, you can see the cilia in a circular
pattern around the tip as well as the band shaped nucleus (shape of a
"C") inside the protist.