Rotifers are commonly called “wheel animalcules” because of the wheel-like movements of the crown of cilia, used for locomotion and/or feeding. Some are less than 100 microns and none are more than 2mm. There are at least 37 marine species (Crothers, 1997) and Pontin (1978) lists 90 brackish and freshwater planktonic species plus many varieties; other freshwater species are benthic and littoral. Almost all are free-living and Pontin gives general distribution data, showing that the majority are cosmopolitan. Galliford (1967) records seven from Dozmary Pool on Bodmin Moor, but otherwise there were only a few Cornish records until William Whiteley took up their study and added many more species. 87 species, mainly non-marine, are listed on the ERICA database 2008.