WALLACE, R.L.: Rotifers: exquisite metazoans

Being among the first microorganisms seen by children exploring the world with their new microscope or high schoolers in biology class, rotifers have fascinated people for nearly 325 years, ever since Leeuwenhoek began describing them in his letters to the Royal Society in London late in the 17th century. And while these organisms have captivated the imagination of many, including writers of science fiction and artists working in glass, they are generally ignored by research biologists, for probably fewer than 350 people world-wide study rotifers on a regular or even irregular basis. Accordingly, rotifer research is still an open field where amateurs and professionals coming lately to the discipline can make an immediate positive impact on our knowledge of these curious little beasties. Possessing an anterior ciliated field (corona) used in locomotion and/or food gathering and a pharynx (mastax) equipped with complex jaws (trophi), rotifers comprise a moderately-sized phylum (=1850 species) of tiny (=100-1,500 �m), bilaterally symmetrical, eutelic metazoans, traditionally grouped with the pseudocoelomates. Rotifers are saccate to cylindrical animals with three prominent regions (corona, trunk, foot) and a body cavity in which are suspended the internal organs. Unfortunately these generalizations grossly oversimplify a rich and fascinating diversity. Chief among their charms for research is their ease of culture (including chemostat technology) and the fact that there is much that remains unknown about the phylum. Here I review the trends in rotifer research over the past 25 years, note the directions of current work, and suggest areas where future efforts may prove profitable. These fields include, but certainly are not limited to, the following: ecology, molecular biology, phylogeny, systematics, biophysics, neurophysiology, biology of aging, and cell and development biology.