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Description of RotifersRotifers (or wheel animalcules) are microscopic animals that can be found in many freshwater environments and in moist soil, on mosses and lichens growing on tree trunks and rocks, in rain gutters and puddles, in soil or leaf litter, on mushrooms growing near dead trees, in tanks of sewage treatment plants, and even on freshwater crustacea and aquatic insect larvae. Most rotifers are very small and can be dwarfed by single-celled protozoa. They are distinguished by having arrays of cilia at one end of the body and these are often used to draw water towards the body (the name "rotifer" means "wheel-bearer" because the action of the cilia was initially interpreted as being like the movement of a wheel). Food is forced into the intestine through a grinding structure called the mastax or trophi. Some species of rotifers swim, others crawl and others attach to the substrate. The body of rotifers is enclosed in a cuticle that is segmented and this permits rotifers to contract and extend. A rotifer consists of four basic regions: head, neck, trunk (body), and the foot. In most species, the head carries the corona (crown) of cilia that draws a vortex of water into the mouth, from which the rotifer obtains its food. The trophi (jaws) are located just behind the mouth in the pharynx (throat). Within the body are the stomach and reproductive organs. The final region of the rotifer body is the foot; this foot ends in a "toe" containing a cement gland with which the rotifer may attach itself to objects. Rotifers are primarily omnivorous, but some species have been known to be cannibalistic. The diet of rotifers most commonly consists of dead or decomposing organic materials, phytoplankton and other protists. Rotifers are in turn prey to carnivorous secondary consumers, including shrimp and crabs. Some species of rotifers consist only of females that produce daughters from unfertilized eggs (a type of reproduction called parthenogenesis). Many rotifers are capable of surviving very harsh conditions such as desiccation - a process known as cryptobiosis.