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Thigmotrichida (class Ciliatea, subclass Holotrichia) An order of ciliate protozoa which have thigmotactic (see THIGMOTAXIS) cilia at the anterior end of the body by means of which the organisms maintain contact with their hosts. They are parasites or commensals (see COMMENSALISM) in molluscs in freshwater and marine habitats. There are two suborders.