Stylonychia is a genus of ciliate, included among the stichotrichs. It is very common in fresh water and soil, found on filamentous algae, surface films, and among particles of sediment. They can also be found swimming on and through decaying vegetation and pond scum floating through the water. Like its relatives, Stylonychia has cilia grouped into membranelles alongside the mouth and cirri over the body. It is distinguished partly by long cirri at the posterior, usually a cluster of three. The largest can just be seen at a 25x magnification, and the smallest can just be seen at a 450x magnification.They are carnivorous and prey on other protozoans and bacteria, such as Urocentrum.
Stylonychia is oval in shape when viewed from the top, and it is notable for its incessant activity and rapid movement. It, like Paramecium and Blepharisma, is a ciliate (having short hair like extensions). The cilia of Stylonychia are more highly specialized and not freely distributed over its body. The cilia along the edge of the ventral surface seem to be tufts of cilia fused together and are used very much like legs allowing the animal to move with a walking motion.Some have small "tufts" of cilli, others have them evenly spread out. Longer fused cilia form stylus-like protrusions at both ends of its body. Another set of specialized cilia beat the water and sweep bacteria and other microorganisms into its oral cavity. Sometimes pieces of their prey can be seen whilst being digested.
Stylonychia has a particularity : it has 48 different mating types, which means that each individual can select its mates within 97 percent of the total population. It is more than most paramecium, but other species do have more than two sexes, for example Tetrahymena thermophila and its 7 different sexes.
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