What are rotifers, beyond tiny organisms that you feed to your reef? Although rotifers are for the most part microscopic, they are in fact multicellular animals belonging to their own ancient group which can be found all over the world.
Rotifers belong to their own phylum, a level of classification below Kingdom (animals, fungi, plants etc.), which means they are morphologically and genetically distinct from other animals at a very base level. Within the rotifer phylum there are three major groupings which are further split into the 2200 species which have been described.
The word rotifer means “wheel-bearer”, which is owed to the cilia that surround the mouth of the animal; when observed, the beating of the cilia resembles the rotation of a wheel. Rotifers use this ring of cilia, called a corona, for feeding on organic waste, algae and protozoans. When they aren’t attached to a substrate, rotifers also use the corona for locomotion.
The rotifer body is made up of roughly 1000 cells, usually reaching lengths of 0.1 to 0.5mm. While most animals grow through cell division, rotifers keep the same number of cells in their bodies for their whole life. Instead growth is achieved by increasing the actual size of the cells.
Reproduction in rotifers happens sexually, parthenogenetically (meaning that females can produce offspring without sperm from from a male), or by a combination of the two depending on the group. In some species males are completely absent.
Rotifers are found all around the world. Most commonly found in freshwater, some species have also adapted to life in brackish and saltwater or even moist locations on land. In these environments they can be planktonic, sessile or even parasitic. The species we culture Brachionus plicatilis (L-type) and Brachionus rotundiformis (S-type) are euryhaline, meaning they can live in a wide range of salinities, making them suitable for use in your reef.
If this short overview of rotifers piqued your interest, here are some other resources you can use to learn more about these fascinating creatures:
http://www.micrographia.com/specbiol/rotife/homebdel/bdel0100.htm