Rotifera

Rotifers are an ecologically and morphologically diverse group of small multicellular invertebrates (body length: 0.03 - 2 mm) that are common to all aquatic and moist, terrestrial habitats. In streams and rivers, rotifers are one of the species-richest invertebrate group, often reaching high abundances in deep streambed sediment-layers1-4,11,12. More importantly, rotifers are central to the biomass and production of systems, as they display the fastest reproductive rate of any metazoan group2,3. Rotifers display a wide range of feeding habits, with species preying on bacteria, algae, protozoans, invertebrates and particulate organic matter4,5 and are prey for protozoans and other freshwater invertebrates such as predatory chironomids and stoneflies6-9, fish and waterfowl.
  Two major groups of mobile rotifers can be easily distinguished: thin, wormlike bdelloid rotifers that contrast to the wide spectrum of forms and shapes of monogonont rotifers10. Bdelloid rotifers are best studied and identified alive, because behavioural characteristics play a critical role in species identification. More detailed information about benthic rotifers and meiofauna can be found at the website of Dr J. M. Schmid-Araya.