The oligotrichs are a group of

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...

s, included among the

spirotrich The spirotrichs are a large and diverse group of ciliate protozoa. They typically have prominent oral cilia in the form of a series of polykinetids, called the adoral zone of membranelles, beginning anterior to the oral cavity and running down ...

s. They have prominent oral

cilia The cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike proj ...

, which are arranged as a collar and lapel, in contrast to the choreotrichs where they form a complete circle. The body cilia are reduced to a girdle and ventral cilia. In ''Halteria'' and its relatives, they form bristles or cirri; however these forms may be closer relatives of the stichotrichs than of other oligotrichs. These organisms are very common in plankton communities, especially in marine systems. Usually found in concentrations of about 1 per ml, they are the most important herbivores in the sea, the first link in the

food chain A food chain is a linear network of links in a food web, often starting with an autotroph (such as grass or algae), also called a producer, and typically ending at an apex predator (such as grizzly bears or killer whales), detritivore (such as ...

. File:643 oligotrich-ciliate.jpg, Oligotrich ciliate, probably ''Strombidium'' File:Halteria.jpg, ''Halteria sp.''

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Further reading