Rotifers comprise a modestly sized phylum (≈1,850 species) of tiny (ca. 50–2,000 μm), bilaterally symmetrical, eutelic metazoans, traditionally grouped within the pseudocoelomates or Aschelminthes. These saccate to cylindrically shaped protostomes possess three prominent regions (corona, trunk, foot). They are distinguished by a ciliated, anterior corona (used in locomotion and food gathering) and a pharynx equipped with a complex set of jaws. Unfortunately, these generalizations grossly oversimplify a rich and fascinating diversity. Chief among the charms of the study of rotifers are their ecological importance, ease of culture (including chemostat technology), and the fact that much remains unknown about this exquisite phylum.