The Collaborative International Dictionary of English v.0.48:

Chlamydomonas \Chlamydomonas\ prop. n.
   The type genus of the Chlamydomonadaceae; they are solitary
   biflagellated plantlike algae common in fresh water and damp
   soil. They multiply freely and are often a pest around
   filtration plants.

   Syn: genus Chlamydomonas.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Chlamydomonas
    n 1: type genus of the Chlamydomonadaceae; solitary doubly-
         flagellated plant-like algae common in fresh water and damp
         soil; multiply freely; often a pest around filtration
         plants [syn: Chlamydomonas, genus Chlamydomonas]