Filter Feeder

An organism that obtains all of its food in the form of fine particulate organic matter (FPOM). Many species of macro invertebrates in the river are filter feeders. Many possess specialized organs for doing so. For example, brush-like hairs around the mouth and forelegs facilitate this kind of feeding behavior in Isonychia bicolor, a species of mayfly. Other species of Ephemeroptera employ intricate nest building in the sandy deposits behind rocks, while most Trichoptera (caddis flies) build silk webs to trap FPOM. Clams, oysters, and a wide variety of coral reef organisms also feed in this fashion.

Links
  http://www.isu.edu/departments/bios/Minshall/publications_reports.htm