The Collaborative International Dictionary of English v.0.48:

Vorticella \Vor`ti*cel"la\, n.; pl. E. Vorticellas, L.
   Vorticellae. [NL., dim. fr. L. vortex. See Vortex.]
   (Zool.)
   Any one of numerous species of ciliated Infusoria belonging
   to Vorticella and many other genera of the family
   Vorticellidae. They have a more or less bell-shaped body
   with a circle of vibrating cilia around the oral disk. Most
   of the species have slender, contractile stems, either simple
   or branched.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vorticella
    n 1: any of various protozoa having a transparent goblet-shaped
         body with a retractile stalk