tintinnid

Tintinnids are a group of small ciliates found in marine and freshwater plankton. They are distinguished by a lorica, or shell, surrounding the cell. The lorica is typically vase-shaped and is often made from secreted mucus plus incorporated particles such as sand grains or diatom frustules. Inside the lorica, tintinnids use their cilia to move and to feed, while the shell provides protection and buoyancy. Sizes commonly range from about 40 to 200 micrometers.

Distribution and habitat vary widely: tintinnids are cosmopolitan, occurring in coastal and open-ocean waters as well as some freshwater systems. They are an important component of the microzooplankton, inhabiting the upper water column where they feed on smaller algae, bacteria, and small planktonic organisms. Their feeding currents are generated by ciliates around the peristome, allowing efficient capture of prey.

Reproduction in tintinnids is primarily asexual, through binary fission, with occasional sexual conjugation observed in some species. The lorica is species-specific in shape and structure, providing taxonomic characters for identification under light microscopy.

Ecological and scientific importance is notable: tintinnids contribute to marine and freshwater carbon and nutrient cycling as grazers of phytoplankton. Their loricae persist as microfossils in sediments, making tintinnids valuable in paleoceanography and biogeographic studies, as well as in monitoring plankton community structure and water quality.