The oligotrichs are a group of ciliate

Ciliate

The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagella but typically shorter and present in much larger numbers with a different undulating pattern than flagella...

 protozoa

Protozoa

Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...

, included among the spirotrich

Spirotrich

The spirotrichs are a large and distinctive 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 to the left side of the mouth. There may also be...

s. They have prominent oral cilia, which are arranged as a collar and lapel, in contrast to the choreotrich

Choreotrich

The choreotrichs are a group of small, marine ciliates. Their name reflects the impression that they appear to dance . The group includes the tintinnids, which produce species-specific loricae , and are important because these may be preserved as microfossils...

s 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 stichotrich

Stichotrich

The stichotrichs are a group of ciliate protozoa, included among the spirotrichs. Like the hypotrichs, with which they were originally classified, they have body cilia fused into cirri, but these are mostly arranged into rows, running along the ventral surface or edges of the cell. Most...

s 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

Food chain

A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...

.