This rotifer builds an elegant tube of what looks like tiny beads which are, in reality, fecal pellets formed by a concavity on the head in which a gland produces a gelatinous secretion which is mixed with its waste material by ciliary action to form pellets which are then added to the tube as the rotifer grows. An amazing process to observe. There are over 2,000 species of rotifers and virtually every genus contains species with strange and surprising characteristics. In some genera, such as Keratella , a single species can exhibit variations in the size, length, and shape of the spines and projections of the lorica to such an extent that earlier microscopists gave many of these variants distinct species status. But the weirdness of the world of rotifers is only beginning.
Rotifers possess a structure called a mastax which is unique in the animal kingdom.
The jaw apparatus is called the trophi and it grinds the food brought down to it by the ciliary action. The trophi consists of a number of structures which show considerable variation. So the taxonomy of rotifers, is as you can imagine, quite taxing. Every rotiferologist is hoping to win a trophy for finding a new kind of trophi. There are eight basic types of mastax and a good textbook on invertebrates will show you their morphology.