Chaetonotus is a group of poorly understood metazoan. Their size range overlaps that of ciliates, with which they are often confused because of the cilia and spines. They are distinguished by two adhesive structures, like a forked tail, at the posterior end of the cell and by the presence of a discrete pharynx. They usually glide rather than swim. Chaetonotus are sensitive to hostile conditions and only appear when treatment conditions are stable.